Open access peer-reviewed chapter

The Impact of Environmental Stresses in the Virulence Traits of Listeria monocytogenes Relevant to Food Safety

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Sofia Araújo Pereira, Ângela Alves, Vânia Ferreira and Paula Cristina Maia Teixeira

Submitted: November 16th, 2017 Reviewed: March 7th, 2018 Published: November 5th, 2018

DOI: 10.5772/intechopen.76287

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Listeria monocytogenes is a foodborne pathogen, which causes listeriosis disease among humans and other animal species. Infections in humans mainly occur in immunocompromised individuals and are caused by the consumption of ready-to-eat and raw food products contaminated with the pathogen. To ensure survival in nature, L. monocytogenes easily adapts to different environmental conditions, and that justifies the hurdles to prevent bacterial growth inside the food chain. Exposure to a single or multiple sublethal stresses, as those impaired by food processing, food matrices, and the gastrointestinal tract, can enhance tolerance of L. monocytogenes to stresses and increase its survival and pathogenesis. This chapter summarizes the current information on the adaptive response of L. monocytogenes to different stresses, namely (1) cold stress, (2) acid stress, (3) osmotic stress, (4) desiccation stress, and (5) high hydrostatic pressure, and the impact of these stresses on L. monocytogenes virulence. The objective is to provide the background information that is necessary for the development of scientifically sound control strategies to improve food safety and to reduce the uncertainty of microbial risk assessments, associated to limited knowledge on the behavior of cells capable to adapt and survive stresses.


  • Listeria monocytogenes
  • stress response
  • virulence

1. Introduction

Listeria monocytogenes is a pathogenic bacterium capable of causing listeriosis disease in humans and other animals. L. monocytogenes has a ubiquitous distribution in the environment [1]. Human listeriosis is on the top five most commonly reported zoonosis under the surveillance of the European Union (EU) and presents the highest case fatality rate, that is, 16.2% [2]. The incidence of invasive forms of the disease is higher in risk groups, such as the elderly, immunocompromised individuals, pregnant women, and newborns. In countries with established surveillance programs, the incidence of listeriosis is reported to be increasing, and the distribution of cases is shifting, primarily affecting elderly persons. In 2016, most cases of listeriosis were reported in individuals over 64 years of age [2]. This is worrisome, as advances in the field of medicine are leading to growing life expectancies; therefore, an increased risk of foodborne listeriosis is expected to occur in the near future.

Listeriosis is an atypical disease with multiple routes of infection, including aerial, cutaneous, transplacental, nosocomial, direct contact, or digestive tract. However, surveillance studies and investigation of recent outbreaks have demonstrated that the most associated transmission pathway to humans is the intake of contaminated food (digestive tract). Ready-to-eat foods, particularly refrigerated foodstuffs, such as milk and dairy products, meat and meat products, raw vegetables, and fruits, have been related to recent outbreaks [3, 4].

The food industry relies on a variety of processing and preservation methods to produce safe and healthy products with adequate shelf life and that are appreciated by consumers. These methods inactivate or inhibit the growth of pathogenic microorganisms such as L. monocytogenes and suppress undesirable chemical and biochemical changes, thereby ensuring food safety and maintaining desirable physical and sensory properties. The methods currently used in food preservation involve physical, chemical, or biological factors. In combination with other strategies, refrigeration, freezing, addition of acidifying agents or curing agents (e.g., sodium chloride and sodium nitrite), radiation and high-pressure processing are the most reliable and used preservation techniques. However, there are studies which demonstrate that L. monocytogenes strains have mechanisms that allow them to survive and resist the stresses caused by these processing methods [5].

This review focuses on key issues such as the molecular mechanisms underlying L. monocytogenes survival and adaptation to stresses caused by different environmental conditions. Since many of the stresses can be found in both food and humans, we will try to correlate these molecular mechanisms with the organism’s virulence. Studies on the development of technologies to control and prevent the contamination of L. monocytogenes in food matrices and food processing facilities are also briefly discussed.


2. Cold stress response

Cold stress adaptation is a fundamental characteristic of L. monocytogenes that markedly contributes to the microorganisms’ dissemination via refrigerated food products. Although most foodborne pathogens are effectively controlled under cooling storage, L. monocytogenes proliferation persists so, cold-stored contaminated foods provide proper conditions for survival and growth of these organisms [6, 7].

L. monocytogenes, as a psychrotolerant bacterium, is able to grow over a wide range of temperatures (1–45°C), although the optimum temperature range is from 30 to 37°C [8]. Cold stress adaptation in L. monocytogenes is mediated through many molecular response mechanisms whose nature remains mainly vague, besides some aspects of this phenomenon have been clarified in model microorganisms.

2.1. Listerial mechanisms of low-temperature resistance

L. monocytogenes response to cold shock comprises the synthesis of cold-shock proteins (CSPs), while during balanced growth at low temperatures, it produces cold acclimation proteins (CAPs). Twelve CSPs and four CAPs were identified as a result of cold stress [9]. The main functions involving CSPs include chaperones involved in DNA recombination course, transcription, translation, and protein folding [10]. The cold adaptation of this pathogen is accompanied by gene expression changes. When cultured at 10°C, L. monocytogenes RNAs are increasingly synthesized compared to growth at 37°C [11]. A higher mRNA expression for chaperone proteases suggests that ClpP, ClpB, and GroEL enzymes may participate in the degradation of damaged or abnormal polypeptides arising due to growth at low temperatures.

Changes in temperature also lead to an alteration in the membrane lipid composition to maintain the ideal membrane fluidity required for proper enzyme activity and transport of solutes [12]. Listeria cell membrane contains high amounts of iso and anteiso, odd-numbered, branched-chain fatty acids (>95%). When grown under refrigeration temperatures, the anteiso-C15:0 represents 65–85% of total membrane fatty acids. When grown at 37°C, predominant fatty acids are anteiso-C15:0 (41–52%), anteiso-C17:0 (24–51%), and iso-C15:0 (2–18%) [13]. Growth at low temperatures also causes an increase of unsaturated fatty acids, which helps enhancing the fluidity of the membrane. Decreasing the growth temperature from 20 to 5°C precedes a switch from iso to anteiso branching (i-C15:0 to a-C15:0) and a fatty acid shortening (a decrease in C17:0). Annous et al. [13] suggested that the growth of L. monocytogenes in refrigerated foods could be controlled by food-grade agents inhibiting the biosynthesis of anteiso-C15:0.

L. monocytogenes growth at low temperatures is also stimulated by the presence of cryoprotectant compatible solutes, for example, betaine, glycine, and carnitine [14, 15]. Listeria imports and accumulates these solutes from the environment, and this is one of the functions of sigma factor σB (Listeria’s general stress transcription factor) during growth at low temperature [16]. In response to cold shock, σB controls the transcription of genes encoding the BetL, Gbu, and OpuC uptake system, involved in the accumulation of glycine, betaine, and carnitine. Studies with mutants having deleted osmolyte transporter genes demonstrated the cryoprotective activity of these compounds [17].


3. Acid stress response

L. monocytogenes may be exposed to high acidity levels while in the food chain and during gastrointestinal (GI) passage in the host (i.e., following exposure to fatty acids, in the phagosome of macrophages during systemic infection, and even upon exiting the host, due to fluctuations in environmental pH).

Being a neutrophile (optimum pH 6 or 7), L. monocytogenes keeps the intracytoplasmic pH close to neutrality, though pH oscillations in the external medium are imperative for its survival and a prerequisite for pathogenesis and infection [18]. Acid tolerance response (ATR) is the adaptive phenomenon that permits the pathogen to preserve pH homeostasis when exposed to low pH. Understanding the molecular mechanisms of acid adaptation and pH homeostasis is essential in order to control the pathogen growth in high-risk foods and predict the ability to cause disease.

3.1. Listerial mechanisms of acid resistance

Cellular exposure to pH stress induces the modulation of fatty acid profiles in Listeria cell membrane, although the changes differ from those documented for other genera [19]. In L. monocytogenes, larger proportions of linear chain fatty acids are incorporated into the membrane, with increased levels of C14:0 and C16:0 and a reported concomitant decrease in C18:0 [20, 21].

Under high acidic environments, two chaperonins (DnaK and GroES) and a serine protease (HtrA) have been identified and characterized in Listeria, being necessary for the organism survival [22, 23, 24]. Other studies shed light on the role of σB in modulating genes involved in pH homeostasis and gastrointestinal persistence, thus crucial in L. monocytogenes survival after exposure to acid conditions. It has been reported that Listeria mutants that lack a sigB functional gene exhibit a decreased resistance to low pH conditions, besides σB regulates the expression of OpuC, a cold-activated transporter for carnitine.

Additional mechanisms of acid resistance such as the F0-ATPase complex, arginine deiminase system (ADI), and the glutamate decarboxylase (GAD) have been elucidated.

3.1.1. F0F1-ATPase complex

F0F1-ATPase is an enzyme organized in two distinct although physically linked domains. The catalytic part (F1) is cytoplasmic while the integral membrane domain (F0) acts as a membrane channel for proton translocation. Cytoplasmic domain may either catalyze the synthesis of adenosine triphosphate (ATP) when the protons pass into the cytoplasm through the membrane-bound domain, or hydrolyze ATP when the protons move outside of the cell. Thus, the F0F1-ATPase complex is responsible for the aerobic synthesis of ATP, as a result of protons moving into the cell, and generates a proton motive force anaerobically by expelling protons. As a consequence of the latter mechanism, F0F1-ATPase is thought to increase intracellular pH in acidic situations [25].

3.1.2. Arginine deiminase system

This system comprises three enzymes: arginine deiminase (encoded by arcA) which catalyzes the hydrolysis of arginine to citrulline and ammonia; ornithine carbamoyltransferase (encoded by arcB) which is responsible for converting citrulline to ornithine and carbamoylphosphate, in the presence of phosphate; and carbamate kinase (encoded by arcC) which synthesizes ATP from carbamoylphosphate and adenosine diphosphate (ADP).

Arginine is transported into the cell in exchange for an ornithine molecule that is moved outside through the transporter encoded by arcD, while the pathway enzymes ultimately catabolize arginine to ornithine, ammonia, and CO2. Ammonia is produced through the catabolization of arginine via the ADI system combined with intracellular protons to produce ammonium ions. This reaction increases intracellular pH, thus allowing survival in hostile environments that would otherwise be lethal to the cell [26]. In addition, ATP is generated by the system and this can be used for driving out protons through F1F0-ATPase [27].

3.1.3. Glutamate decarboxylase system

The GAD enzyme, generally encoded by gadA or gadB, irreversibly decarboxylates glutamate, producing the neutral γ-aminobutyrate (GABA). This reaction results in an increase of the cytoplasmic pH due to the consumption of an intracellular proton. GABA produced by the decarboxylation reaction is subsequently exchanged on the cell membrane for a glutamate molecule by a glutamate: GABA antiporter, generally encoded by the gadC gene [28].

The GAD system is crucial for L. monocytogenes acid adaptation and, consequently, for a successful passage through the gastric environment, a necessary condition for latter invasion of intestinal epithelial cells [29]. The loss of genes encoding a GAD enzyme and a glutamate transporter decreases the cell’s ability to survive in low pH environments and consequently to cause infection [30]. Stress factors commonly associated with the GI tract (low pH, anaerobiosis, hypo- and hyperosmotic shock, bile salts, and chloride ions) have been shown to induce GAD system expression in a variety of bacteria [31, 32].


4. Osmotic stress response

Osmotic stress defines the osmotic strength variation of an organism environment, which results from desiccation or from a high content of osmotically active compounds (salt or sugars) in the environment, lowering its water activity (aw). Since the bacterial cytoplasmic membrane is permeable to water but not to most other metabolites, hyper- or hypo-osmotic shock causes an efflux or influx of water, accompanied by a concomitant decrease or an increase in intracellular volume, respectively. In general, the internal osmotic pressure is higher than that of the surrounding medium, generating turgor, the driving force for cell extension, growth, and division. Therefore, the bacterial maintenance of pressure turgor is critical to survival in osmotic stress conditions.

The maximum NaCl concentration that permits L. monocytogenes growth ranges from 7 to 10% [33]. This osmotolerance is vital during its infectious cycle, since L. monocytogenes encounters elevated osmolarity in the food processing industry and in the gastrointestinal lumen of the host. The response of microorganisms to osmotic stress is called osmoadaptation and holds physiological changes and variations in gene expression patterns [34].

4.1. Listerial mechanisms of osmotic resistance

Compatible solute osmoadaptation is a biphasic response in which elevated levels of potassium cation K+ (and glutamate, its counter-ion) represent a primary response, succeeded by a significant increase in cytoplasmic concentration of compatible solutes. Cells absorb osmolytes from the external environment to restore osmotic balance within cells. The solute-mediated osmoprotection stimulates the growth of cells subjected to high salt concentrations. Deletions of these osmolyte transporters reduce the growth of Listeria under conditions of hyperosmolarity [14, 30, 35]. In addition to previously mentioned compatible solutes (glycine, betaine, and carnitine), proline is important for the survival under hyperosmolarity conditions [36]. σB factor, as an important part of the overall stress response of L. monocytogenes, mediates the expression of ctc gene and the use of betaine and carnitine as osmoprotectors.

In response to osmotic stress, two genes involved in cell envelope modification have been identified: lmo2085, a putative peptidoglycan-linked protein, and lmo1078, a putative UDP-glucose phosphorylase that catalyzes the formation of UDP-glucose, a precursor of membrane glycolipids and of the cell wall [37].

A further mechanism of osmotic adaptation is the modification of genetic expression leading to an increased or a decreased synthesis of several proteins. Salt-shock proteins are rapidly induced and overexpressed for a short time period, being similar to those induced in cold-shock response (CSPs and CAPs). Among CSPs induced in L. monocytogenes, there are two general stress response proteins, DnaK that acts as a heat-shock protein stabilizing cellular proteins and Ctc that is involved in high osmolarity resistance in the lack of osmoprotectants, such as glycine, betaine, and carnitine, in the medium [38]. Additional stress response proteins, including ClpC (an ATPase), ClpP (a protease), and HtrA (a protease), are essential for osmotic and acid stress adaptation in L. monocytogenes [39]. HtrA may play a role in degrading misfolded proteins and is beneath LisRK control, a two-component regulatory system important for osmoregulation [36].


5. Desiccation stress response

Desiccation tolerance defines the bacteria’s aptitude to survive for extended periods on a surface, deficient of nutrients and water. As so, L. monocytogenes desiccation tolerance is most likely associated with the ability to persist in food production surfaces and consequently cross-contaminate food products [40]. The low aw resulting from high osmolarity decreases turgor pressure in a bacterial cell inhibiting bacterial growth [41]. Drying and addition of salt or sugar are traditional methods to lower food aw and therefore enhance its prolonged shelf life. L. monocytogenes grows optimally at aw ≥ 0.97, although it may survive in foods with low aw [42]. When compared to other common infectious foodborne pathogens, L. monocytogenes does not appear to grow at aw < 0.90 but it can survive in these conditions, particularly under refrigeration, for long periods. To date, existing information regarding L. monocytogenes desiccation survival is limited and primarily focuses on factors influencing the survival to osmotic stress [40, 43, 44, 45, 46]. Strains of serotypes 1/2c and 1/2b were the most tolerant to desiccation, followed by 4b and 1/2a [47]. Hansen and Vogel [46] showed the protective effect of osmoadaptation and also the formation of biofilms on the desiccation survival.


6. High hydrostatic pressure

A high hydrostatic pressure (HHP) represents the application of pressure in the range of 50–1000 MPa, though the inactivation of vegetative cells of bacterial species is typically reached from 300 to 700 MPa, and bacterial spores inactivation demands higher pressure levels up to 1000 MPa [48]. However, depending on the pressure level, HHP treatments can fully inactivate bacteria or impose sublethal injuries. For pressures up to 400 MPa, the integrity of Gram-positive bacterial cells and metabolic activity are maintained, with very limited cell destruction [49]. Over the last years, it has been stated that L. monocytogenes is potentially capable of recovering culturability following HHP exposure [49, 50, 51, 52]. Physiological studies have also demonstrated that increasing pressure levels results in an accelerated decline of metabolic indicators, such as the activity of the LmrP membrane transport system [53]. These findings suggest that bacteria exposed to HHP are unable to grow due to cell injury, but yet can mount a nonspecific response to high pressure. A proportion of the cell population is able to maintain cellular activity of some kind after HHP, demonstrating the capacity to cellular repair and regrow, when adequate conditions are available [49].

To date, little research has been conducted regarding the mechanisms of bacterial adaptation and resistance to high pressure. Wemekamp-Kamphuis et al. [54] demonstrated that one of the responses that enable Listeria survival upon HHP treatment results from induction of the general stress response mediated by σB. L. monocytogenes sigB deletion mutant was more susceptible to HHP exposure than the wild type, while induction of σB resulted in an increased HHP protection relative to the untreated control strain.

Several pressure-induced proteins have been increasingly synthesized when compared to the synthesis of other control proteins at atmospheric pressure [55]. L. monocytogenes has shown to actively express many genes as a response to high pressure, but some functional categories appear more affected than others. Genes that tend to be expressed at higher levels under high pressure are genes encoding for transport and binding, signal transduction and chemotaxis, cellular processes, transcriptional regulators, metabolism, and protein fate [56]. The stabilization and maintenance of the bacteria cell is at high focus, showed by the significant regulation of ribosomes and proteins, together with components involved in the cell envelope and the septal ring. It is assumed that the activation of genes involved in the lipid and peptidoglycan biosynthetic pathways is connected to this function. Upregulation of genes associated with generalized repair and maintenance has been proved, where the activation of cold- and heat-shock genes is an example for this [57, 58]. When high pressure demands more energy to be used on repair, energy production and conversion is suppressed. The repression of several energy production/conversion, carbohydrate, and other carbon compound catabolic genes may represent a diminishment of catabolism in cells imposed by HPP treatments. This can be seen by the pressure-induced switch from active growth to a cell repair state, the stationary phase, resulting in a decreased growth rate [59].

Several genes associated with cell formation and shape, as well as synthesis or reassembly of cell-wall constituents, in particular peptidoglycan and fatty acids, were observed to have an increased expression. Because of this, genes involved in such functions can be considered as very central in the response to high pressure. It is presumed that L. monocytogenes increases both cell division and cell-envelope-associated gene expression aiming to replace damaged components and thus compensate membrane and wall damages [59].

Cell membranes damage by HPP may possibly be a main cause of inactivation or death in Gram-negative bacteria, but it is fallacious to admit that in Gram-positive bacteria. Cell membrane and wall stabilization in the stationary growth phase do provide a protective effect against HPP, being a major factor for the survival of HPP-induced damage [60]. Beyond cell envelope damage, HPP interferes within the nascent septal ring formation along with other associated cell-wall formation and chromosome segregation processes [59].


7. Stress impact on L. monocytogenes virulence

L. monocytogenes has a profound ability to adapt to unfavorable stressful environments, switching from a saprophyte to an intracellular pathogen capable of causing serious infection to the host [61]. In this transformation, σB dominates both in the external environment and during gastrointestinal transit, while positive regulatory factor A (PrfA) plays a central role on the intracellular infection. In concert with PrfA, σB activates the transcription of several L. monocytogenes virulence genes: (1) bsh, encoding bile salt hydrolase, essential in gastrointestinal colonization prior to invasion; (2) inlA, encoding internalin A, mediates entry into human intestinal epithelial cells; and (3) gadA, encoding part of the glutamate decarboxylase system, crucial for acid survival [62]. σB also contributes to the transcriptional activation of prfA, encoding PrfA, a central virulence regulator of virulence gene expression in L. monocytogenes [63].

PrfA-dependent virulence gene cluster or LIPI-1 (Listeria pathogenicity island 1) encodes most virulence factors involved in the pathogenic infectious cycle. This chromosomal locus comprises the following genes: (1) hly, encoding listeriolysin O (LLO), a pore-forming toxin crucial in the escape from phagocytic vacuoles; (2) plcA and plcB, encoding two phospholipases C which cooperate with LLO in the escape from bacterial phagosomes; (3) mpl, encoding a metalloprotease implicated in the maturation of proenzyme pro-PlcB; (4) actA, encoding ActA protein involved in the intra- and intercellular motility of the bacteria; and (5) prfA, encoding PrfA, a transcriptional activator of LIPI-1 genes [64]. The expression of additional genes dispersed on the chromosome may be PrfA-regulated, as the internalin locus inlAB [65], the genes encoding internalins InlA and InlB cell-wall-anchored proteins which induce Listeria phagocytosis [66].

Following the complete genome sequencing of several L. monocytogenes strains, an increasing number of virulence-related proteins are being identified and their specific involvement during infectious stages deciphered (Table 1).

Positive regulatory factor A, central virulence regulator of virulence gene transcription.
SigmaB (σB)
General stress transcription factor.
Class III stress-response regulator, a transcription repressor.
Heat regulation at controlling inverted repeat of chaperone expression elements. A transcription repressor.
Attachment and invasionInlA
Internalin A, surface protein that mediates entry into cells expressing its receptor, the E-cadherin.
Internalin B, surface protein that mediates entry into cells expressing one of the receptors gC1qR, HGF-SF, Met, and the glycosaminoglycanes (GAGs).
Lysis of vacuolesLLO
Listeriolysin O, hemolysin required for vacuole escape by lysis of the phagosome membrane.
Phospholipase activated by proteolytic cleavage involving Mpl or by cellular proteases. Required for the lysis of the double-membrane vacuole.
Metalloprotease required for the maturation of PC-PLC.
Intracellular multiplicationHpt
Hexose phosphate transporter required for intracytosolic proliferation.
Cell-to-cell spreadActA
Actin assembly-inducing protein, involved in cell-to-cell spread.
Environmental stress response and virulenceHtrA
Serine protease involved in acid and osmotic stress response.
Bile salt hydrolase involved in the intestinal and hepatic phases of listeriosis.
ATPase protein promoting early bacterial escape from the phagosome of macrophages and thus virulence.
Serine protease involved in proteolysis and required for growth under stress condition.
Chaperone heat-shock proteins encoded by the dnaK operon and required for phagocytosis.
GroES, GroEL
Chaperone proteins which regulate HrcA posttranscriptionally.
The glutamate decarboxylase system, involved in acid stress response.
Glycine betaine transport system I, involved in osmotic stress response.
Glycine betaine transport system II, involved in osmotic stress response.
Carnitine transport system, involved in cold and osmotic stress response.

Table 1.

Stress response and virulence-associated proteins in Listeria monocytogenes (adapted from reference [67]).

In addition to other factors, the infectious potential of L. monocytogenes is conditioned by the environmental conditions prior to host invasion. A correlation between stress response and virulence seems to exist and associates strains having more effective stress response mechanisms to being also more virulent [84]. Early studies by Durst [84] and Wood and Woodbine [85] demonstrated that cold storage may enhance virulence of some strains because the pathogen virulence rather increases when grown under refrigeration than at optimal growth temperature. By contrast, virulence gene expression was reported to be downregulated at temperatures below 30°C, besides PrfA is only formed at 37°C [85]. According to Loh et al. [86], the expression of prfA is nearly 16-times higher at 37°C compared to that at 30°C, and imperceptible in cells cultivated at 20°C. The specific pathogenicity of LLO can be fully recovered in less than 24 h by incubating refrigerated cells at 37°C [87]. This virulence recovery after heat shock reinforces the importance of eliminating L. monocytogenes from minimally processed ready-to-eat foods held at refrigeration temperatures for long periods.

Low pH and high salt content are common factors often found in foods contaminated with L. monocytogenes [89]. Even though at these conditions, the growth of most foodborne and spoilage bacteria is restricted, L. monocytogenes is capable of surviving and even grow in such environments; long-term adaptation to these sublethal stress conditions results in altered virulence [88].

Conte et al. [31, 89] demonstrated that short-term exposure (1 h) of L. monocytogenes to a sublethal acidic environment (pH 5.1) not only increased its invasiveness to the human colon adenocarcinoma cell line Caco-2 but also increased the ability of L. monocytogenes to survive and proliferate in macrophage-like cells, suggesting that exposure to a low pH (e.g., in the human stomach) may enhance listerial overall virulence. In addition, LLO excreted by virulent L. monocytogenes showed a maximal activity at pH 4.0–5.0. In another study, the exposure of L. monocytogenes to acidic shock has induced the transcription of two important virulence genes (inlA and bsh) [90]. Conversely, a study by Rieu et al. [91] reported a decrease in virulence gene transcription after 5 h at pH 4.0 achieved with acetic acid. This conflicting finding may be sustained by the use of organic acids since they might be more harmful to the bacteria. Some weak organic acids enhance pathogenicity of the bacterium, while others reduce it, as the secretion of LLO is increased by citrate, acetate, and lactate, whereas sorbate inhibited this hemolysin [92]. This knowledge would be important for the selection of acidulants to be used in different foods.

Garner et al. [93] reported an intensified invasiveness of L. monocytogenes for Caco-2 cells when grown at 7°C rather than at 37°C, and, for both temperatures, the invasion ability was greater in cells grown at pH 7.4 compared to growth at pH 5.5. A growth temperature of 37°C, pH 7.4, in the presence of NaCl or sodium lactate, enhanced L. monocytogenes invasiveness; however, the pre-exposure to gastric fluid (pH 4.5), even for as short as 10 s, substantially reduced its invasion. These findings intimate that listerial virulence-associated characteristics seem to be affected by specific food properties (e.g., the presence of organic acids or salt). The authors further showed that L. monocytogenes growth phase affects its ability to invade Caco-2 cells. The invasion by log-phase cells was 9.5-fold lower than invasion by stationary-phase cells, corroborating other studies which demonstrate that exposure of L. monocytogenes to different environmental conditions can change invasiveness and virulence [93]. Accordingly, the increased stationary-phase invasiveness also coincides with stationary-phase induction of σB activity [90]. In stationary-phase cells, inlA expression is regulated in a σB-dependent manner, and growth phase-dependent effects on invasion appear independent of PrfA [94, 95], contributing to inlA transcription [96].

Complementary studies demonstrate that L. monocytogenes pathogenicity requires an adaptive acid tolerance response, so the ability to survive gastric acid fluid and to invade host cells is related to ATR activation [30, 89, 97]. This finding is supported by the fact that the glutamate decarboxylase (GAD) system, as the ATR most important component, is required for listerial survival in the gastric environment, and also LisRK deletion, a two-component system involved in acid resistance regulation, caused a dramatic reduction in virulence [29, 98].

A further prerequisite for L. monocytogenes infection depends on the ability to counteract conditions of elevated osmolarity in the gastrointestinal tract. As mentioned in Section 2.1, the carnitine uptake system (OpuC) is directly linked to osmotic stress resistance of L. monocytogenes and to its ability to reach and proliferate in the liver and spleen [17]. Carnitine (produced from the desquamation of the gastrointestinal epithelial layer) was formerly proved to act as a crucial osmoprotectant, facilitating growth in this gastrointestinal environment, once changing the carnitine transported OpuC resulted in a significant reduction in Listeria ability to colonize the upper small intestine and cause subsequent systemic infection [99, 100]. A supporting study by Wemekamp-Kamphuis et al. [17] demonstrated that a triple mutant, defective in all three compatible uptake systems (BetL, Gbu, and OpuC), showed a similar phenotype to that of a single opuC mutant, mutually revealing a decreased ability to cause systemic infection relative to the parent. Those were clear evidences that betL and gbu do not play a significant role in L. monocytogenes pathogenesis and that it is the carnitine uptake system that most induces listerial virulence. In addition, Joseph et al. [101] also identified OpuCA and OpuCB as being induced intracellularly. Since the contribution of each transporter is dependent on the external environment, there are occurrences when each system is tailored for optimal effects within a certain environmental niche.

Over the last years, novel trends in food production tend to preserve the natural flavor and texture of products using minimal processing. Non-thermal food preservation usually allows a significant microbial reduction, and mounting evidence also demonstrates that the conditions applied by alternative technologies may influence bacterial virulence [102]. The application of HHP has been shown not to induce mutations in the internal genes, inlA and inlB, implicated in the adhesion and internalization of L. monocytogenes in human cells. However, when the effect of HPP on the ctsR gene is observed, a reduction in virulence potential of surviving cells was noted. Likewise, virulence and reduced motility may be the result of a mutation in this gene corresponding to the loss of a single amino acid. This suppression could be related to a high-pressure tolerance [70, 103].


8. Conclusions

Exposure of L. monocytogenes to sublethal environmental stresses can enhance its survival to subsequent lethal conditions and additionally induce the expression of the organism’s virulence genes. Therefore, exposure of L. monocytogenes to food-associated stresses such as high salt concentrations or low temperatures during refrigerated storage may result in increased virulence and thus a higher risk for listeriosis. Any strain of L. monocytogenes present in food is actually considered equally pathogenic. However, results from several studies support the idea that the heterogeneity among strains regarding the response to stress and virulence potential should be considered, once responses to food matrix and storage conditions are often strain specific.

Although significant advances in our understanding on stress response and virulence potential have been achieved in the last years, there is still a need to fulfill knowledge gaps on molecular mechanisms behind L. monocytogenes response to stress and virulence. Further studies on the influence of food matrix on stress tolerance and virulence potential of different strains, recovered from foods and from patients, are needed. This information can be further used by regulators to refine previous risk assessments and also in the definition of control measures by the food industry.



This work was supported by National Funds from FCT—Fundação para a Ciência e a Tecnologia through project UID/Multi/50016/2013. Publication in open access was co-financed by the project NORTE-01-0246-FEDER-000011, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). Financial support for author Sofia Pereira was provided by ESF—European Social Fund, under the PORTUGAL 2020 Partnership Agreement, through doctoral fellowship NORTE-08-5369-FSE-000007_BD_1.


  1. 1. Saavedra L, Bellomio A, Hebert EM, Minahk C, Suarez N, Sesma F. Listeria: Epidemiology, pathogenesis and novel potential treatments. In: Romano A, Giordano CF, editors. Listeria Infections: Epidemiology, Pathogenesis and Treatment. New York: Nova Science Publishers, Incorporated; 2012. pp. 67-98
  2. 2. EFSA. The European Union summary report on trends and sources of zoonoses, zoonotic agents and food-borne outbreaks in 2016. EFSA Journal. 2017;15(12):56-78
  3. 3. Magalhães R, Almeida G, Ferreira V, Santos I, Silva J, Mendes MM, Pita J, Mariano G, Mâncio I, Sousa MM, Farber J, Pagotto F, Teixeira P. Cheese-related listeriosis outbreak, Portugal, March 2009 to February 2012. Euro Surveillaince. 2015;20(17):pii=21104
  4. 4. Callejón RM, Rodríguez-Naranjo MI, Ubeda C, Hornedo-Ortega R, Garcia-Parrilla MC, Troncoso AM. Reported foodborne outbreaks due to fresh produce in the United States and European Union: Trends and causes. Foodborne Pathogens and Disease. 2015 Jan;12(1):32-38
  5. 5. Lou Y, Yousef AE. Adaptation to sublethal environmental stresses protects Listeria monocytogenes against lethal preservation factors. Applied and Environmental Microbiology. 1997;63(4):1252-1255
  6. 6. Junttila JR, Niemelä SI, Hirn J. Minimum growth temperatures of Listeria monocytogenes and non-haemolytic Listeria. The Journal of Applied Bacteriology. 1988 Oct;65(4):321-327
  7. 7. Walker SJ, Archer P, Banks JG. Growth of Listeria monocytogenes at refrigeration temperatures. The Journal of Applied Bacteriology. 1990 Feb;68(2):157-162
  8. 8. Seeliger HPR, Jones D. Listeria. In: Sneath PHA, Mair NS, Sharpe NE, Holt JG, editors. Bergey’s Manual of Systematic Bacteriology. Vol 2. Baltimore: Williams and Wilkins; 1986. pp. 1235-1245
  9. 9. Bayles DO, Annous BA, Wilkinson BJ. Cold stress proteins induced in Listeria monocytogenes in response to temperature downshock and growth at low temperatures. Applied and Environmental Microbiology. 1996 Mar;62(3):1116-9
  10. 10. Schmid B, Klumpp J, Raimann E, Loessner MJ, Stephan R, Tasara T. Role of cold shock proteins in growth of Listeria monocytogenes under cold and osmotic stress conditions. Applied and Environmental Microbiology. 2009 Mar;75(6):1621-1627
  11. 11. Liu S, Graham JE, Bigelow L, Ii PDM, Wilkinson BJ. Identification of Listeria monocytogenes genes expressed in response to growth at low temperature. Applied and Environmental Microbiology. 2002;68(4):1697-1705
  12. 12. Mansilla MC, Cybulski LE, Albanesi D, de Mendoza D. Control of membrane lipid fluidity by molecular thermosensors. Journal of Bacteriology. 2004 Oct;186(20):6681-6688
  13. 13. Annous BA, Becker LA, Bayles DO, Labeda DP, Wilkinson BJ. Critical role of anteiso-C15:0 fatty acid in the growth of Listeria monocytogenes at low temperatures. Applied and Environmental Microbiology. 1997 Oct;63(10):3887-3894
  14. 14. Angelidis AS, Smith GM. Role of the glycine betaine and carnitine transporters in adaptation of Listeria monocytogenes to chill stress in defined medium. Applied and Environmental Microbiology. 2003 Dec;69(12):7492-7498
  15. 15. Lou MM, Smith LT. Gbu glycine betaine porter and carnitine uptake in osmotically stressed Listeria monocytogenes cells. Applied and Environmental Microbiology. 2002 Nov;68(11):5647-5655
  16. 16. Bayles DO, Wilkinson BJ. Osmoprotectants and cryoprotectants for Listeria monocytogenes. Letters in Applied Microbiology. 2000 Jan;30(1):23-27
  17. 17. Wemekamp-Kamphuis HH, Wouters JA, Sleator RD, Gahan CGM, Hill C, Abee T. Multiple deletions of the osmolyte transporters BetL, Gbu, and OpuC of Listeria monocytogenes affect virulence and growth at high osmolarity. Applied and Environmental Microbiology. 2002 Oct;68(10):4710-4716
  18. 18. Bearson S, Bearson B, Foster JW. Acid stress responses in enterobacteria. FEMS Microbiology Letters. 1997 Feb;147(2):173-180
  19. 19. Fozo EM, Quivey RG. The fabM gene product of streptococcus mutans is responsible for the synthesis of monounsaturated fatty acids and is necessary for survival at low pH. Journal of Bacteriology. 2004;186(13):4152-4158
  20. 20. van Schaik W, Gahan CG, Hill C. Acid-adapted Listeria monocytogenes displays enhanced tolerance against the lantibiotics nisin and lacticin 3147. Journal of Food Protection. 1999 May;62(5):536-539
  21. 21. Ryan S, Hill C, Gahan CGM. Acid stress responses in Listeria monocytogenes. Advances in Applied Microbiology. 2008;65:67-91
  22. 22. Hanawa T, Fukuda M, Kawakami H, Hirano H, Kamiya S, Yamamoto T. The Listeria monocytogenes DnaK chaperone is required for stress tolerance and efficient phagocytosis with macrophages. Cell Stress Chaperones. 1999 Jun;4(2):118-128
  23. 23. Gahan CGM, O’Mahony J, Hill C. Characterization of the groESL operon in Listeria monocytogenes: Utilization of two reporter systems (gfp and hly) for evaluating in vivo expression. Infection and Immunity. 2001 Jun;69(6):3924-3932
  24. 24. Wilson RL, Brown LL, Kirkwood-Watts D, Warren TK, Lund SA, King DS, et al. Listeria monocytogenes 10403S HtrA is necessary for resistance to cellular stress and virulence. Infection and Immunity. 2006 Jan;74(1):765-768
  25. 25. Cotter PD, Gahan CG, Hill C. Analysis of the role of the listeria monocytogenes F0F1-AtPase operon in the acid tolerance response. International Journal of Food Microbiology. 2000 Sep;60(2-3):137-146
  26. 26. Ryan S, Begley M, Gahan CGM, Hill C. Molecular characterization of the arginine deiminase system in Listeria monocytogenes: Regulation and role in acid tolerance. Environmental Microbiology. 2009 Feb;11(2):432-445
  27. 27. Lucas PM, Blancato VS, Claisse O, Magni C, Lolkema JS, Lonvaud-Funel A. Agmatine deiminase pathway genes in lactobacillus brevis are linked to the tyrosine decarboxylation operon in a putative acid resistance locus. Microbiology. 2007 Jul;153(7):2221-2230
  28. 28. Karatzas K-AG, Suur L, O’Byrne CP. Characterization of the intracellular glutamate decarboxylase system: Analysis of its function, transcription, and role in the acid resistance of various strains of Listeria monocytogenes. Applied and Environmental Microbiology. 2012 May;78(10):3571-3579
  29. 29. Cotter PD, Gahan CG, Hill C. A glutamate decarboxylase system protects Listeria monocytogenes in gastric fluid. Molecular Microbiology. 2001 Apr;40(2):465-475
  30. 30. Gandhi M, Chikindas ML. Listeria: A foodborne pathogen that knows how to survive. International Journal of Food Microbiology. 2007 Jan;113(1):1-15
  31. 31. Conte MP, Petrone G, Di Biase AM, Longhi C, Penta M, Tinari A, et al. Effect of acid adaptation on the fate of Listeria monocytogenes in THP-1 human macrophages activated by gamma interferon. Infection and Immunity. 2002 Aug;70(8):4369-4378
  32. 32. Jydegaard-Axelsen A-M, Hoiby PE, Holmstrom K, Russell N, Knochel S. CO2- and anaerobiosis-induced changes in physiology and gene expression of different Listeria monocytogenes strains. Applied and Environmental Microbiology. 2004 Jul;70(7):4111-4117
  33. 33. Lado BH, Yousef AE. Characteristics of Listeria monocytogenes important to food processors. In: Ryser T, Marth EH, editors. Listeria, Listeriosis and Food Safety. Boca Raton, FL: CRC Press; 2007. pp. 157-214
  34. 34. Hill C, Cotter PD, Sleator RD, Gahan CGM. Bacterial stress response in Listeria monocytogenes: Jumping the hurdles imposed by minimal processing. International Dairy Journal. 2002;12:273-283
  35. 35. Wemekamp-kamphuis HH, Sleator RD, Wouters JA, Hill C, Abee T. Molecular and physiological analysis of the role of osmolyte transporters BetL, Gbu, and OpuC in growth of Listeria monocytogenes at low temperatures. Applied and Environmental Microbiology. 2004;70(5):2912-2918
  36. 36. Sleator RD, Hill C. Bacterial osmoadaptation: The role of osmolytes in bacterial stress and virulence. FEMS Microbiology Reviews. 2002 Mar;26(1):49-71
  37. 37. Utratna M, Shaw I, Starr E, O’Byrne CP. Rapid, transient, and proportional activation of σ(B) in response to osmotic stress in Listeria monocytogenes. Applied and Environmental Microbiology. 2011 Nov;77(21):7841-7845
  38. 38. Duché O, Trémoulet F, Glaser P, Labadie J. Salt stress proteins induced in Listeria monocytogenes. Applied and Environmental Microbiology. 2002 Apr;68(4):1491-1498
  39. 39. Wonderling LD, Wilkinson BJ, Bayles DO. The htrA (degP) gene of Listeria monocytogenes 10403S is essential for optimal growth under stress conditions. Applied and Environmental Microbiology. 2004 Apr;70(4):1935-1943
  40. 40. Vogel BF, Hansen LT, Mordhorst H, Gram L. The survival of Listeria monocytogenes during long term desiccation is facilitated by sodium chloride and organic material. International Journal of Food Microbiology. 2010 Jun 15;140(2-3):192-200
  41. 41. Amezaga M, Davidson I, McLaggan D, Verheul A, Abee T, Booth I. The role of peptide metabolism in the growth of Listeria monocytogenes ATCC 23074 at high osmolarity. Microbiology. 1995 Jan;141(1):41-49
  42. 42. Nolan DA, Chamblin DC, Troller JA. Minimal water activity levels for growth and survival of Listeria monocytogenes and Listeria innocua. International Journal of Food Microbiology. 1992 Aug;16(4):323-335
  43. 43. Zoz F, Iaconelli C, Lang E, Iddir H, Guyot S, Grandvalet C, et al. Control of relative air humidity as a potential means to improve hygiene on surfaces: A preliminary approach with Listeria monocytogenes. Almeida A, editor. PLoS One. 2016 Feb;11(2):e0148418
  44. 44. Overney A, Chassaing D, Carpentier B, Guillier L, Firmesse O. Development of synthetic media mimicking food soils to study the behaviour of listeria monocytogenes on stainless steel surfaces. International Journal of Food Microbiology. 2016 Dec;238:7-14
  45. 45. Hingston PA, Piercey MJ, Hansen LT. Genes associated with desiccation and osmotic stress in Listeria monocytogenes as revealed by insertional mutagenesis. Applied and Environmental Microbiology. 2015 Aug;81(16):5350-5362
  46. 46. Hansen LT, Vogel BF. Desiccation of adhering and biofilm Listeria monocytogenes on stainless steel: Survival and transfer to salmon products. International Journal of Food Microbiology. 2011 Mar;146(1):88-93
  47. 47. Hingston P, Chen J, Dhillon BK, Laing C, Bertelli C, Gannon V, et al. Genotypes associated with Listeria monocytogenes isolates displaying impaired or enhanced tolerances to cold, salt, acid, or desiccation stress. Frontiers in Microbiology. 2017 Mar;8:369
  48. 48. Smelt JPP. Recent advances in the microbiology of high pressure processing. Trends in Food Science & Technology. 1998 Apr;9(4):152-158
  49. 49. Ritz M, Pilet MF, Jugiau F, Rama F, Federighi M. Inactivation of salmonella Typhimurium and listeria monocytogenes using high-pressure treatments: Destruction or sublethal stress? Letters in Applied Microbiology. 2006;42(4):357-362
  50. 50. Jantzen MM, Navas J, de Paz M, Rodriguez B, da Silva WP, Nunez M, et al. Evaluation of ALOA plating medium for its suitability to recover high pressure-injured Listeria monocytogenes from ground chicken meat. Letters in Applied Microbiology. 2006 Sep;43(3):313-317
  51. 51. Bozoglu F, Alpas H, Kaletunç G. Injury recovery of foodborne pathogens in high hydrostatic pressure treated milk during storage. FEMS Immunology and Medical Microbiology. 2004 Apr;40(3):243-247
  52. 52. Bull MK, Hayman MM, Stewart CM, Szabo EA, Knabel SJ. Effect of prior growth temperature, type of enrichment medium, and temperature and time of storage on recovery of Listeria monocytogenes following high pressure processing of milk. International Journal of Food Microbiology. 2005;101(1):53-61
  53. 53. Kilimann K, Hartmann C, Delgado A, Vogel R, Ganzle M. A fuzzy logic-based model for the multistage high-pressure inactivation of ssp. MG 1363. International Journal of Food Microbiology. 2005 Jan;98(1):89-105
  54. 54. Wemekamp-Kamphuis HH, Wouters JA, de Leeuw PPLA, Hain T, Chakraborty T, Abee T. Identification of sigma factor B-controlled genes and their impact on acid stress, high hydrostatic pressure, and freeze survival in Listeria monocytogenes EGD-e. Applied and Environmental Microbiology. 2004 Jun;70(6):3457-3466
  55. 55. Welch TJ, Farewell A, Neidhardt FC, Bartlett DH. Stress response of Escherichia coli to elevated hydrostatic pressure. Journal of Bacteriology. 1993 Nov;175(22):7170-7177
  56. 56. Liu Y, Ream A. Gene expression profiling of Listeria monocytogenes strain F2365 during growth in ultrahigh-temperature-processed skim milk. Applied and Environmental Microbiology. 2008 Nov;74(22):6859-6866
  57. 57. Malone AS, Chung Y-K, Yousef AE. Genes of Escherichia coli O157:H7 that are involved in high-pressure resistance. Applied and Environmental Microbiology. 2006 Apr;72(4):2661-2671
  58. 58. Scortti M, Monzó HJ, Lacharme-Lora L, Lewis DA, Vázquez-Boland JA. The PrfA virulence regulon. Microbes and Infection. 2007 Aug;9(10):1196-1207
  59. 59. Bowman JP, Bittencourt CR, Ross T. Differential gene expression of Listeria monocytogenes during high hydrostatic pressure processing. Microbiology. 2008;154(2):462-475
  60. 60. Mañas P, Mackey BM. Morphological and physiological changes induced by high hydrostatic pressure in exponential- and stationary-phase cells of Escherichia coli: Relationship with cell death. Applied and Environmental Microbiology. 2004 Mar;70(3):1545-1554
  61. 61. Freitag NE, Port GC, Miner MD. Listeria monocytogenes—From saprophyte to intracellular pathogen. Nature Reviews. Microbiology. 2009 Sep;7(9):623-628
  62. 62. Kazmierczak MJ, Mithoe SC, Boor KJ, Wiedmann M. Listeria monocytogenes sigma B regulates stress response and virulence functions. Journal of Bacteriology. 2003 Oct;185(19):5722-5734
  63. 63. Nadon CA, Bowen BM, Wiedmann M, Boor KJ. Sigma B contributes to PrfA-mediated virulence in Listeria monocytogenes. Infection and Immunity. 2002;70(7):3948
  64. 64. Leimeister-Wächter M, Haffner C, Domann E, Goebel W, Chakraborty T. Identification of a gene that positively regulates expression of listeriolysin, the major virulence factor of listeria monocytogenes. Proceedings of the National Academy of Sciences of the United States of America. 1990;87(21):8336
  65. 65. Gaillard JL, Berche P, Frehel C, Gouln E, Cossart P, Gouin E, et al. Entry of L. monocytogenes into cells is mediated by internalin, a repeat protein reminiscent of surface antigens from gram-positive cocci. Cell. 1991 Jun;65(7):1127-1141
  66. 66. Kuhn M, Goebel W. Internalization of listeria monocytogenes by nonprofessional and professional phagocytes. In: Oelschlaeger TA, Hacker JH, editors. Bacterial Invasion into Eukaryotic Cells Subcellular Biochemistry. Vol. 33. Boston, MA: Springer; 2000. pp. 411-436
  67. 67. Roche SM, Velge P, Liu D. Virulence determination, section II identification and detection. In: Liu D, editor. Handbook of Listeria monocytogenes. Boca Raton: CRC Press, Taylor & Francis Group; 2008. pp. 241-270
  68. 68. Kreft J, Vázquez-Boland JA. Regulation of virulence genes in Listeria. International Journal of Medical Microbiology. 2001;291:145-157
  69. 69. Wiedmann M, Arvik TJ, Hurley RJ, Boor KJ. General stress transcription factor sigmaB and its role in acid tolerance and virulence of Listeria monocytogenes. Journal of Bacteriology. 1998 Jul;180(14):3650-3656
  70. 70. Karatzas KAG, Wouters JA, Gahan CGM, Hill C, Abee T, Bennik MHJ. The CtsR regulator of Listeria monocytogenes contains a variant glycine repeat region that affects piezotolerance, stress resistance, motility and virulence. Molecular Microbiology. 2003 Sep;49(5):1227-1238
  71. 71. van der Veen S, Abee T. HrcA and DnaK are important for static and continuous-flow biofilm formation and disinfectant resistance in listeria monocytogenes. Microbiology. 2010 Dec;156(12):3782-3790
  72. 72. Bierne H, Cossart P. InlB, a surface protein of Listeria monocytogenes that behaves as an invasin and a growth factor. Journal of Cell Science. 2002 Sep;115(Pt 17):3357-3367
  73. 73. Cossart P, Vicente MF, Mengaud J, Baquero F, Perez-Diaz JC, Berche P. Listeriolysin O is essential for virulence of listeria monocytogenes: Direct evidence obtained by gene complementation. Infection and Immunity. 1989 Nov;57(11):3629-3636
  74. 74. Marquis H, Doshi V, Portnoy DA. The broad-range phospholipase C and a metalloprotease mediate listeriolysin O-independent escape of Listeria monocytogenes from a primary vacuole in human epithelial cells. Infection and Immunity. 1995 Nov;63(11):4531-4534
  75. 75. Poyart C, Abachin E, Razafimanantsoa I, Berche P. The zinc metalloprotease of Listeria monocytogenes is required for maturation of phosphatidylcholine phospholipase C: Direct evidence obtained by gene complementation. Infection and Immunity. 1993 Apr;61(4):1576-1580
  76. 76. Chico-Calero I, Suarez M, Gonzalez-Zorn B, Scortti M, Slaghuis J, Goebel W, et al. Hpt, a bacterial homolog of the microsomal glucose-6-phosphate translocase, mediates rapid intracellular proliferation in Listeria. Proceedings of the National Academy of Sciences. 2002 Jan;99(1):431-436
  77. 77. Kocks C, Gouin E, Tabouret M, Berche P, Ohayon H, Cossart P. L. monocytogenes-induced actin assembly requires the actA gene product, a surface protein. Cell. 1992 Feb;68(3):521-531
  78. 78. Stack HM, Sleator RD, Bowers M, Hill C, Gahan CGM. Role for HtrA in stress induction and virulence potential in Listeria monocytogenes. Applied and Environmental Microbiology. 2005 Aug;71(8):4241-4247
  79. 79. Dussurget O, Cabanes D, Dehoux P, Lecuit M, Buchrieser C, Glaser P, et al. Listeria monocytogenes bile salt hydrolase is a PrfA-regulated virulence factor involved in the intestinal and hepatic phases of listeriosis. Molecular Microbiology. 2002 Aug;45(4):1095-1106
  80. 80. Rouquette C, de Chastellier C, Nair S, Berche P. The ClpC ATPase of Listeria monocytogenes is a general stress protein required for virulence and promoting early bacterial escape from the phagosome of macrophages. Molecular Microbiology. 1998 Mar;27(6):1235-1245
  81. 81. Gaillot O, Pellegrini E, Bregenholt S, Nair S, Berche P. The ClpP serine protease is essential for the intracellular parasitism and virulence of Listeria monocytogenes. Molecular Microbiology. 2000 Mar;35(6):1286-1294
  82. 82. Sleator RD, Gahan CG, Abee T, Hill C. Identification and disruption of BetL, a secondary glycine betaine transport system linked to the salt tolerance of Listeria monocytogenes LO28. Applied and Environmental Microbiology. 1999 May;65(5):2078-2083
  83. 83. Angelidis AS, Smith LT, Hoffman LM, Smith GM. Identification of opuC as a chill-activated and osmotically activated carnitine transporter in Listeria monocytogenes. Applied and Environmental Microbiology. 2002 Jun;68(6):2644-2650
  84. 84. Roche SM, Gracieux P, Milohanic E, Albert I, Virlogeux-Payant I, Temoin S, et al. Investigation of specific substitutions in virulence genes characterizing phenotypic groups of low-virulence field strains of Listeria monocytogenes. Applied and Environmental Microbiology. 2005 Oct;71(10):6039-6048
  85. 85. Johansson J, Mandin P, Renzoni A, Chiaruttini C, Springer M, Cossart P. An RNA thermosensor controls expression of virulence genes in Listeria monocytogenes. Cell. 2002 Sep;110(5):551-561
  86. 86. Loh E, Dussurget O, Gripenland J, Vaitkevicius K, Tiensuu T, Mandin P, et al. A trans-acting Riboswitch controls expression of the virulence regulator PrfA in Listeria monocytogenes. Cell. 2009 Nov;139(4):770-779
  87. 87. Buncic S, Avery SM, Rogers AR. Listeriolysin O production and pathogenicity of non-growing Listeria monocytogenes stored at refrigeration temperature. International Journal of Food Microbiology. 1996 Aug;31(1-3):133-147
  88. 88. Cole MB, Jones MV, Holyoak C. The effect of pH, salt concentration and temperature on the survival and growth of Listeria monocytogenes. The Journal of Applied Bacteriology. 1990 Jul;69(1):63-72
  89. 89. Conte M, Petrone G, Di Biase A, Ammendolia M, Superti F, Seganti L. Acid tolerance in Listeria monocytogenes influences invasiveness of enterocyte-like cells and macrophage-like cells. Microbial Pathogenesis. 2000 Sep;29(3):137-144
  90. 90. Sue D, Fink D, Wiedmann M, Boor KJ. Sigma B-dependent gene induction and expression in Listeria monocytogenes during osmotic and acid stress conditions simulating the intestinal environment. Microbiology. 2004 Nov;150(11):3843-3855
  91. 91. Rieu A, Guzzo J, Piveteau P. Sensitivity to acetic acid, ability to colonize abiotic surfaces and virulence potential of Listeria monocytogenes EGD-e after incubation on parsley leaves. Journal of Applied Microbiology. 2010 Feb;108(2):560-570
  92. 92. Kouassi Y, Shelef LA. Listeriolysin O secretion by Listeria monocytogenes in broth containing salts of organic acids. Journal of Food Protection. 1995;58(12):1314-1319
  93. 93. Garner MR, James KE, Callahan MC, Wiedmann M, Boor KJ. Exposure to salt and organic acids increases the ability of Listeria monocytogenes to invade Caco-2 cells but decreases its ability to survive gastric stress. Applied and Environmental Microbiology. 2006;72(8):5384-5395
  94. 94. Kim H, Boor KJ, Marquis H. Listeria monocytogenes B contributes to invasion of human intestinal epithelial cells. Infection and Immunity. 2004 Dec;72(12):7374-7378
  95. 95. Kim H, Marquis H, Boor KJ. B contributes to Listeria monocytogenes invasion by controlling expression of inlA and inlB. Microbiology. 2005 Oct;151(10):3215-3222
  96. 96. Dramsi S, Kocks C, Forestier C, Cossart P. Internalin-mediated invasion of epithelial cells by Listeria monocytogenes is regulated by the bacterial growth state, temperature and the pleiotropic activator prfA. Molecular Microbiology. 1993 Sep;9(5):931-941
  97. 97. O’Driscoll B, Gahan CG, Hill C. Adaptive acid tolerance response in Listeria monocytogenes: Isolation of an acid-tolerant mutant which demonstrates increased virulence. Applied and Environmental Microbiology. 1996 May;62(5):1693-1698
  98. 98. Cotter PD, Emerson N, Gahan CG, Hill C. Identification and disruption of lisRK, a genetic locus encoding a two-component signal transduction system involved in stress tolerance and virulence in Listeria monocytogenes. Journal of Bacteriology. 1999 Nov;181(21):6840-6843
  99. 99. Sleator RD, Francis GA, O’Beirne D, Gahan CGM, Hill C. Betaine and carnitine uptake systems in Listeria monocytogenes affect growth and survival in foods and during infection. Journal of Applied Microbiology. 2003;95(4):839-846
  100. 100. Sleator RD, Gahan CGM, O’Driscoll B, Hill C. Analysis of the role of betL in contributing to the growth and survival of Listeria monocytogenes LO28. International Journal of Food Microbiology. 2000 Sep;60(2-3):261-268
  101. 101. Joseph B, Przybilla K, Stuhler C, Schauer K, Slaghuis J, Fuchs TM, et al. Identification of Listeria monocytogenes genes contributing to intracellular replication by expression profiling and mutant screening. Journal of Bacteriology. 2006 Jan;188(2):556-568
  102. 102. van Schaik W, Abee T. The role of σB in the stress response of Gram-positive bacteria—Targets for food preservation and safety. Current Opinion in Biotechnology. 2005 Apr;16(2):218-224
  103. 103. Van Boeijen IKH, Casey PG, Hill C, Moezelaar R, Zwietering MH, Gahan CGM, et al. Virulence aspects of Listeria monocytogenes LO28 high pressure-resistant variants. Microbial Pathogenesis. 2013 Jun;59-60:48-51

Written By

Sofia Araújo Pereira, Ângela Alves, Vânia Ferreira and Paula Cristina Maia Teixeira

Submitted: November 16th, 2017 Reviewed: March 7th, 2018 Published: November 5th, 2018