Open access peer-reviewed chapter

The Genus Enterococcus and Its Associated Virulent Factors

Written By

Hassan Bin-Asif and Syed Abid Ali

Submitted: 16 April 2019 Reviewed: 08 August 2019 Published: 29 October 2019

DOI: 10.5772/intechopen.89083

From the Edited Volume

Microorganisms

Edited by Miroslav Blumenberg, Mona Shaaban, Abdelaziz Elgaml

Chapter metrics overview

1,591 Chapter Downloads

View Full Metrics

Abstract

Enterococci, the Gram-positive, catalase negative, non-spore forming and aero-tolerant fermentative organisms form the second largest group of bacteria studied with reference to microbial source tracking in view of their ability to survive adverse environmental conditions and adaptable nature to revolutionize from low number commensals to a predominant population of host microbiota thus creating a consequence for pathogenesis. Despite being a member of normal human intestinal flora, they are not regarded anymore as generally recognized as safe (GRAS) organisms and some of its species may turned out to be a major cause of nosocomial infections. Ecological and epidemiological studies showed that these bacteria enter in the environment via feces and colonize because of their high adaptability. The main contributors in pathogenesis of enterococci are the presence of various virulence factors and antibiotic resistance genes. This chapter aims to highlight the infections caused by enterococci and their respective virulent determinants.

Keywords

  • enterococcus
  • virulence
  • resistance
  • hemolysis
  • lactic acid bacteria
  • nosocomial infections

1. Introduction

Enterococci (ENT), the Gram-positive (G +ve), catalase negative, benzidine negative, non-spore forming and aero-tolerant fermentative organisms form the second largest group of bacteria studied with reference to microbial source tracking (MST) [1, 2]. It is a non-filamentous microorganism but some species like E. casseliflavus and E. gallinarum exhibit motility by scanty flagella. They produce lactic acid [L (+)- lactic acid enantiomer in case of glucose fermentation] by homofermentative Embden-Meyerhof-Parnas pathway, hence called Lactic Acid Bacteria (LAB). All the species except E. faecalis [(E. fl) (which contains lysine alanine 2–3 type)] contains lysine-D-asparagine linkages with D-isoasparagine as cross bridge in peptidoglycan. Their ability to survive in adverse environmental conditions and adaptable nature revolutionize them from low number commensals to a predominant population of host microbiota which ultimately results in creating a consequence for their pathogenesis [3]. Despite being a member of normal human intestinal flora, they are not regarded as GRAS (Generally Recognized As Safe) organisms anymore [4] as some of its species have turned out to be a major cause of nosocomial infections including hepatobiliary sepsis, urinary tract infections (UTI), surgical wound infections, endocarditis, bacteremia and neonatal sepsis [5]. From a medical perspective, ENT have been recognized as an important hospital acquired pathogen due to their ability to transfer or acquire resistance genes via chromosomal exchange as well as plasmid or transposon (Figure 1). This can lead to increment in dangerous nosocomial infections, thus limiting therapeutic options [6]. This is the reason for exploitation of this genus as an important key indicator bacterium for humans and veterinary resistance surveillance system [7].

Figure 1.

Bacterial mobile genetic elements.

Advertisement

2. Enterococcal infections and their treatments

Over the past few decades, members of the genus Enterococcus have emerged as an important nosocomial pathogen causing different infections. Their transformation from gut commensal to pathogen is attributed by increasing antibiotic resistance especially resistance to vancomycin, high-level aminoglycosides (HLA), and penicillin is of interest. Moreover, resistance to new antimicrobial agents, like linezolid, quinupristin/dalfopristin, and daptomycin has also been emerged (Figure 2). Being more resistant than E. fl, E. faecium (E. fm) has come out to be the leading cause of multidrug resistant (MDR) infections in U.S. Because of its resistance to vancomycin, ampicillin and high-level aminoglycosides, infections caused by this species is very difficult to treat. According to National Healthcare Safety Network (NHSN) report, majority of device associated infections (for example, central lines infections, urinary drainage catheters infection and ventilator infections) were caused by 80% vancomycin and 90.4% ampicillin resistant E. faecium [8]. Other enterococcal species including E. avium, E. casseliflavus, E. durans, E. hirae, E. raffinosus, E. gallinarum and E. mundtii accounts for less human’s infection [9]. Enterococci can cause variety of infections directly as sole cause of an infection or indirectly as a contributor in co-infection with other microorganisms [10] (Figure 3).

Figure 2.

Examples of recently approved drugs.

Figure 3.

Different infections caused by genus Enterococcus.

Enterococcal infections particularly those caused by vancomycin resistant enterococci (VRE) are associated with prolonged hospital stay and excess mortality. World Health Organization (WHO), in its report published in February 2017 placed Vancomycin Resistant E. faecium in the “HIGH PRIORITY category in global priority pathogens list (global PPL)” of antibiotic resistant bacteria to help in prioritizing the research and development of new and effective antibiotic treatments [11, 12]. Earlier to this, VRE was also categorized as “microorganisms with a threat level of serious” with estimated 20,000 drugs resistant enterococcal infections, 1300 death tolls and 66,000 Enterococcus infections per year in United States [13].

2.1 Urinary tract infections (UTIs)

UTIs including prostatitis, epididymitis and cystitis are the most common types of infections caused by ENT. Majority of the patients includes older men as compared to young women. Upper UTIs which lead to bacteremia also occurred in young men [14]. According to a report presented to NHSN by center of disease control and prevention (CDC), Enterococcus spp. account for 14.9% of the total catheter associated UTIs between 2006 and 2007 [8]. Moreover, it is also reported that 15% of UTIs occur in ICU setting with VRE being the major health care associated pathogen [15].

2.2 Intra-abdominal, pelvic and soft tissue infections

ENT are often recovered as a component of mixed microbial flora from cultures of pelvic, soft tissues and intra-abdominal infections. They rarely cause monomicrobial infections at these sites. Enterococcal bacteremia is accompanied with intra-abdominal and pelvic abscesses and wounds; this is the reason why many clinicians prescribe antibiotic regimens for infections at these sites [14, 16, 17]. Moreover, ENT are frequently found in cultures from foot ulcers, decubiti and in diabetics in association with osteomyelitis [15]. Tigecycline, a semi synthetic, bacteriostatic in nature analogue of TET is active against many Gram negative (G −ve) and G +ve bacteria has been used use for the treatment of skin, intra-abdominal and soft tissue infections [18].

2.3 Bacteremia

Incidence of enterococcal blood stream infections are rising day by day [19]. Starting from 6th position in early 80’s, ENT is now the 2nd most common cause of health care associated bacteremia [8]. Bacteremia is designated as a major cause of mortality with Enterococcus spp. being the third and fourth most common etiological agent of blood stream infections in U.S and Denmark, respectively [20, 21, 22]. Genitourinary tract, intra-abdominal, biliary sources, soft tissues infections and indwelling central lines are the common sources of bacteremia from which ENT are isolated as a polymicrobial component [17]. Although enterococcal bacteremia occurs in patients with underlying immunity and illnesses, it rarely affects distant organs or cause metastatic abscesses. Usage of inappropriate antibiotics or late treatment is associated with excess mortality [19]. However, some studies found no decrease in mortality with appropriate antibiotic treatment [23, 24], while some revealed a better outcome after using appropriate antibiotics both for vancomycin and high-level gentamicin resistant enterococci [25, 26].

2.4 Endocarditis

Endocarditis is one of the major enterococcal infections for which antibiotic treatment is difficult because of enterococci’s intrinsic resistance to many antibiotics. First case report of endocarditis with details of clinical and pathological description of a strain called Micrococcus zymogens (Enterococcus faecalis) was published in 1899 [27]. Since then this species is responsible for 8–17% of all infective endocarditis (IE) cases affecting mainly elderly patients with prosthetic heart valve, degenerative heart valve diseases, urinogenital or GIT infections leading to bacteremia and becoming third most frequent etiologic agent of both native and prosthetic valve IE [28, 29, 30]. In certain cases, dual antibiotic therapy including aminoglycoside (preferably gentamicin) and cell-wall synthesis inhibitor (vancomycin or β-lactam) is required for IE therapy.

American Heart Association (AHA) and European Society of Cardiology (ESC) recommends 4 to 6 weeks of combined antibiotic treatment with success rate of 80%. Due to nephrotoxic effects of long-term aminoglycoside usage, Danish guidelines on endocarditis treatment endorsed aminoglycoside usage but for 2 weeks only [30]. In case of VRE and HLGR enterococcal IE, surgery remains the only option to remove the infected valve [15]. Among Enterococcus spp., E. fl was thought to be the most common causative agent of endocarditis infecting mostly older persons as compared to women [31, 32] but recently a more problematic MDR strain of E. fm belonging to well characterized hospital-associated clade was also identified as a cause of IE. The strains of E. fm has high resistance against first line antibiotics (i.e., MIC >64 mg/L ampicillin and vancomycin) due to which their application in curing IE is obsolete [33, 34]. In response to this, AHA recommends Quinupristin-dalfopristin (Q/D; 30% Streptogramin B and 70% A) and linezolid as alternate to treat MDR E. fm IE [35]. In fact, many reports suggest better efficacy of Q/D (24 g/day) when use in combination with imipenem, levofloxacin, doxycycline, rifampicin, high-dose ampicillin [36, 37]. Two main and critical steps in the pathogenesis of IE are attachment to tissues and production of biofilm. Biofilm associated proteins which facilitates occurrence of IE includes aggregation substance protein, i.e., Asc10 [38], microbial surface components recognizing adhesive matrix molecules (MSCRAMM) proteins ace for E. fl [39] and acm for E. fm [40], esp and its homolog in E. fm, espfm [41, 42], endocarditis and biofilm associated pili of E. fl, i.e., ebp [42, 43, 44]. The main complication of enterococcal IE is heart failure occurring in half of the patients. Moreover, MDR E. fm is also an important factor in increasing epidemiology of enterococcal IE because >90% of E. fl are susceptible to ampicillin and vancomycin [45].

Advertisement

3. Pathogenesis and virulence associated with enterococci

Virulence factors are potential traits that define the pathogenesis of most infections which involves a series of events namely, colonization, adhesion to the host’s cells, tissue invading and resistance to non-specific defensive mechanisms. Researchers are encouraged to characterize the factors involved in etiology of infections caused by pathogenic ENT in immunocompromised or impaired immunity patients. Two major classes of virulent factors have been well characterized: (1) surface factors that promote colonization in host cells, and (2) protein and peptides secreted by ENT that damage the tissues [46].

3.1 Gelatinase (gelE), serine protease (sprE) and fsr regulator

Gelatinase is a zinc metalloprotease expressed extracellularly and hydrolyze gelatin, collagen and casein [47]. It is proved to be a full virulence factor expressed in mouse model of peritonitis, endocarditis [48, 49], endophthalmitis [50], in nematode [51] and in vitro translocation [52]. It is encoded by gelE and sprE operon and expressed in regulation by a quorum sensing system encoded by the fsr locus [53]. The fsr locus (E. flregulator) is a well characterized locus containing fsrA, fsrB, fsrC and fsrD genes which is homologs to staphylococcal agrBCA loci [54]. A signaling peptide in fsrB liberates gelatinase biosynthesis activating pheromone (GBAP) peptide by auto-processing and a quorum sensing system. gelE and sprE genes are induced when GBAP accumulates from exponential to stationary phase. Fsr regulon is present above the sprE and gelE and encode a serine protease and gelatinase, respectively [55]. Possible molecular mechanism behind the expression of gelE and sprE is shown in Figure 4 [56]. Epidemiological data suggests the involvement of fsr locus and gelatinase in virulence traits, like adhesion capacity (biofilm) established by processing of C-terminal gelatinase protein [57, 58].

Figure 4.

Flow diagram showing the possible mechanism of gelE and sprE gene expression.

3.2 Catalase (EC 1.11.1.6)

Catalase is a renowned enzyme present in all three domains of life. It catalyzes the decomposition of hydrogen peroxide (HP) to water and oxygen, protecting the cell from oxidative damage of HP. HP is a reactive oxygen species (ROS) in biosphere. It is produced as a by-product in aerobic metabolism such as in oxygen activation, in photosynthetic and respiratory electron transport chain and as product of oxidases activity. First step of catalase reaction is the reduction of HP to water forming cationic heam radical and an oxoiron [compound 1 (FeIV═O ion)]. In the second step, dismutation is completed by the reaction of a second HP, resulting in the release of oxygen and water. The enzyme is regenerated in the resting FeIII state. NADPH binding catalases prevent the build-up of an inactive partially oxidized dead-end form of the enzyme called compound II [59].

Catalases are of three types: Prokaryotic Mn-catalases (minor bacterial protein family), bifunctional catalase peroxidases (not found in plants and animals and exhibit both catalytic and peroxidative activities) and haem catalases (most abundant group found in Archaebacteria, Eubacteria, Fungi, Protista, Animalia and Plantae). Despite catalyzing the same reaction (2H2O2 → 2H2O + O2), all three families differ in architecture of active site and mode of reaction [60]. Among G +ve lactic acid bacteria (LAB), E. fl are unable to make porphyrin compounds, including heam groups. It exhibits catalase activity but only when it is grown in heme containing medium [61]. E. fl catalase (katA) is a homo-tetrameric protein containing only one heme group (protoheme IX) and belongs to the group of heme containing mono functional catalases [62]. In the absence of heme, E. fl produces NADH peroxidase (Npr) that degrades HP to water. Factors involve in biogenesis of catalase was not known until Baureder and Hederstedt [62] carried out a research in which they used two different transposon systems to construct libraries of E. fl mutants and screened for clone defective in catalase activity by using colony zymogram staining procedure. They identified nine genes (in addition to katA, which codes for catalase enzyme protein) distributed over five chromosomal loci which are important for expression of catalase activity in E. fl. The proteins encoded by those genes have diverse functions such as NADH oxidation and HP detoxification (npr), global regulation of RNA turnover (rnjA, srmB), membrane transport (oppBC) and/or stress response (etaR) [62].

3.3 Hyaluronidase (EC 4.2.2.1)

These are the enzymes capable of degrading hyaluronate (Hyaluronic acid, hyaluronan) found in several body parts, like umbilical cord, synovial fluid, cartilage, brain, muscles and extracellular matrix (ECM) in connective tissues. Almost half of the total body hyaluronate is found in the skin. The viscous ground substance release by the connective tissues provides a barrier for the entry of bacteria or toxin into the body. However, ground substance contains hyaluronate as a major component which is degraded by hyaluronidases. Rooster’s combs and certain bacteria like streptococci also produce hyaluronidases [63]. Many pathogenic bacteria release some extracellular products which helps them in damaging the tissue thus acting as a virulent factor and smoothen the progress of bacterial toxin into the tissues and are commonly named as “spreading factors.” Bacterial hyaluronidases (BH) are among some of the spreading factors released by certain G +ve and G −ve bacteria. BH belongs to the third type of hyaluronidases commonly called as hyaluronate lyases. They eliminate β 1–4 linkage resulting in the production of unsaturated disaccharides by acting as endo-N-acetylhexosaminidases [63]. Different models of E. fm trans conjugant’s virulence that harbors conjugative mega plasmid have been reported [64, 65] to carried hyl gene. According to some previous studies, the hyl gene was more prevalent in clinical isolates rather than community base isolates. According to a recent study, hyl gene is considered as a passive marker of virulence because deletion of this gene caused no effect on mouse peritonitis model [66, 67].

3.4 Cytolysin (Cyt)

Enterococcal Cyt is a broad range prokaryotic and eukaryotic lysin usually plasmid encoded. It is reported to enhance virulence of E. fl in animal models. It was originally described as lanthionine-containing bacteriocins of G +ve bacteria [68]. The Cyt operon is a part of E. fl PAI consisting of 6 genes related to toxin biosynthesis and two promoters namely PL (involve in regulation of transcription of genes related to toxin structure and function) and PREG (involve in transcription of regulatory genes) and present near esp gene [69]. Like gelatinase, expression of Cyt is quorum sensing dependent and regulated by two component systems [70]. The regulatory system of Cyt consists of two open reading frames (ORFs) namely cylR1 and cylR2 which encodes a transmembrane protein of unknown function (cylR1) and a helix-turn-helix DNA binding protein (cylR2) [71]. The Cyt operon is either present on conjugative pheromone responsive plasmid such as pAD1 [72] or encoded by chromosome within 150 kb PAI [73, 74]. Todd et al. [75] conducted the first comprehensive study on hemolysin molecule after the observation of hemolysis zones on blood agar plates produced by E. fl. Increased virulence due to Cyt in E. fl was first described in the study of Ike and colleagues [76] through dose dependent intraperitoneal injections of E. fl strains harboring plasmid pAD1 which encodes Cyt. Later, various researchers showed the lyses of mouse erythrocytes, macrophages, and PMNs or death of experimental animals/organism like mouse, rabbits and C. elegans with Cyt [58, 73, 77, 78, 79, 80]. Self-lysis of Cyt producing cells is prevented by an unknown mechanism. However, immunity proteins or ABC transporters protects other lantibiotic producing bacteria from self-lysis [81, 82]. In E. fl, a zinc metalloprotease and transmembrane protein, CylI (immunity factor) is shown to protect from Cyt mediated bacterial cell death [83].

Despite having a virulence face, Cyt can also act as beneficiary trait for both E. fl and its host. Possible beneficial activities might include, acting as colonization factor, providing self-defense against something which is more harmful (probably an intestinal parasite), facilitating nutrient acquisition from prokaryotic or eukaryotic sources, function as signaling molecule to monitor bacterial population size and probe the environment for target cells and last but not the least, bacteriocin activity of Cyt allows E. fl to occupy a novel host niche which non-cytolytic bacteria cannot access [68, 84, 85].

3.5 Enterococcal surface protein (esp)

Esp, a putative virulent factor is found in both E. fl and E. fm. It is located on pathogenicity island (PAI) at the surface of the bacterium [56]. It was initially identified in a highly virulent gentamicin resistant strain of E. fl [69]. Esp shares global structural similarity with Streptococcus agalactiae Rib [86], S. pyogenes R28, C-alpha protein, and S. aureus Bap (biofilm associated protein) [87]. These similarities are restricted to a highly conserved region within the C repeat units of Esp proteins and group A and B of streptococcal proteins of streptococci and nonrepeat N-terminal region of Bap protein [71]. Bap protein from S. aureus is associated with biofilm formation and shares a sequence and structural similarity with Esp. Esp is also associated with E. fl biofilm formation on different surfaces, like polysterylene plates and hospital equipment like catheters, prosthetic heart valves, orthopedic appliances, artificial cardiac pace makers [47], ureteral stents [88], intravascular catheters [89], silicone gastrostomy devices [90], and biliary stents [91].

A variant of Esp is also reported in E. fm isolates [92]. E. fm esp is predominantly present in nosocomial settings in contrast to E. fl esp which is widely distributed among environmental strains [93, 94]. Expression of esp is affected by environmental conditions like temperature (maximum at 37°C) and availability of oxygen, i.e., under anaerobiosis [56]. Several research groups demonstrated the role of E. fm esp in pathogenesis of experimental endocarditis, UTIs, and bacteremia. While no specific role of esp was found in peritonitis, and colonization of GIT [95, 96]. Role of esp was also established by a genetic approach. In a study conducted by Tendolkar et al. [97], esp-lacking E. fl strains produced biofilm in large amounts after successful induction and expression of esp gene. In contrast, several studies suggest that esp is not necessary for biofilm formation [98, 99]. Study conducted by Kristich et al. [100] demonstrated that E. fl OG1RF produced biofilms not only in the absence of esp and entire PAI that harbors it. In other studies, conducted on clinical enterococcal isolates, majority of the esp-negative isolates produced biofilms and no correlation was found among esp gene and biofilm forming capacity [89, 101].

3.6 Aggregation substance (AS)

AS is a group of proteins encoded by pheromone-induced conjugative plasmids. AS directed bacteria to aggregate which results in close cell contact between donor and recipient. Several studies showed that AS mediated internalization of E. fl by cultured human intestinal epithelial cells and increased in vitro adhesion to cultured renal tubular cells [102]. Among the best studied AS proteins are Asa I, Asp I, and Acs 10 encoded by asa1, aspI and prgB genes of conjugated plasmids pAD1 and pCF10, respectively, and shows >90% sequence identity [56, 66]. These proteins contain an N-terminal domain, a central domain, a variable region and two Arg-Gly-Asp (RGD) motifs which are also found in fibronectin and associated with integrin binding proteins [102, 103]. Apart from their function in conjugation transfer, these RGD motifs are also involve in eukaryotic cell binding and binding to renal epithelial cells [102]. It is demonstrated in a study that central domain and N-terminal domain are responsible for aggregation of Asc 10 [104]. Beside its role in conjugation, AS also serves as a virulence factor in E. fl by promoting cell-cell contact, adhesions to host cells and ECM proteins (including thrombospondin, fibronectin, vitronectin, and collagen type I), increased vegetation in experimental endocarditis, resistance to killing by polymorphonuclear leukocytes (PMNs) by inhibition of respiratory burst (production of ROS) in the macrophages, increased cell surface hydrophobicity [71]. All the proteins aid in the pathogenesis of AS in E. fl, like Asa I increases adherence to human macrophages and renal tubular cells, Asc 10 facilitates internalization and intracellular survival in PMNs [74, 103, 105]. Both Asa I and Asc 10 increase virulence of E. fl in rabbit endocarditis model by increasing adherence to certain ECM proteins [79, 106].

Advertisement

4. Conclusions

In conclusion, acquired resistance to certain antibiotics is an important feature of the genus Enterococcus. Persistent use of antibiotics in humans and animals for therapy and as growth promoters plus the presence of insertion sequences, transposons, integerons and plasmids make them large reservoirs of transferable antibiotic resistance and virulence genes in various ecosystems including soil, water, and food. Due to its rapid popularity, as resistant bacteria, ENT serves as an important key indicator in the surveillance of many humans and veterinary resistance profile. Adherence capability plus antibiotic resistance make them more problematic for effective therapeutic decisions. Till now only food consumption is considered as an option for the spread of antibiotic resistant bacteria to humans but the detection of resistant bacteria in soil opens a new route for the exposure of environmental antibiotic resistance to humans. Results of different studies from our lab concludes that soil, poultry, animals and birds carried high burdens of ENT which are fully armed with potential virulent and antibiotic resistance genes [107, 108, 109, 110]. In Pakistan, there is paucity of information regarding prevalence, types and genetic characteristics of enterococci along with their resistance/virulence genes and clones especially from clinical and other environmental sources. In this respect, regular environmental monitoring using most advance molecular genotyping (Tables 1 and 2) as routine testing is recommended. Genes mirror the requirements of life. As our understanding of enterococcal genomics grows, bacterial genomics will become an important tool for providing new insights into the nature, biology and habitats of the enterococci. Presence of insertion sequence (IS16) gene in soil isolates verified the dissemination of hospital associated ENT into the environment via inappropriate handling of hospital wastes [108]. It is therefore also recommended to dispose clinical/hospital waste properly and appropriately.

Virulent factorsGenePrimer sequence (5′-3′)Product length (bp)Reference
Biofilm associated genesespTIMCTT-TGA-TTC-TTG-GTT-GTC-GGA-TAC
TCC-AAC-TAC-CAC-GGT-TTG-TTT-ATC
475[111]
aggAAG-AAA-AAG-AAG-TAG-ACC-AAC
AAA-CGG-CAA-GAC-AAG-TAA-ATA
1553[112]
acmGGC-CAG-AAA-CGT-AAC-CGA-TA
CGC-TGG-GGA-AAT-CTT-GTA-AA
353[113]
efaAfmAAC-AGA-TCC-GCA-TGA-ATA
CAT-TTC-ATC-ATC-TGA-TAG-TA
735[92]
efaAfsGAC-AGA-CCC-TCA-CGA-ATA
AGT-TCA-TCA-TGC-TGT-AGT-A
705
asaGCA-CGC-TAT-TAC-GAA-CTA-TGA
TAA-GAA-AGA-ACA-TCA-CCA-CGA
375[114]
aceAAA-GTA-GAA-TTA-GAT-CCA-CAC
TCT-ATC-ACA-TTC-GGT-TGC-G
320[115]
ccfGGG-AAT-TGA-GTA-GTG-AAG-AAG
AGC-CGC-TAA-AAT-CGG-TAA-AAT
542[112]
cpdTGG-TGG-GTT-ATT-TTT-CAA-TTC
TAC-GGC-TCT-GGC-TTA-CTA
782
cobAAC-ATT-CAG-CAA-ACA-AAG-C
TTG-TCA-TAA-AGA-GTG-GTC-AT
1405
eepGAG-CGG-GTA-TTT-TAGTTC-GT
TAC-TCCAGCATTGGATGCT
937
Gelatinase operon genesgelEACC-CCG-TAT-CAT-TGG-TTT
ACG-CAT-TGC-TTT-TCC-ATC
419[116]
sprETTG-AGC-TCC-GTT-CCT-GCC-GAA-AGT-CAT-TC
TTG-GTA-CCG-ATT-GGG-GAA-CCA-GAT-TGA-CC
591
fsrAATG-AGT-GAA-CAA-ATG-GCT-ATT-TA
CTA-AGT-AAG-AAA-TAG-TGC-CTT-GA
740
fsrBGGG-AGC-TCT-GGA-CAA-AGT-ATT-ATC-TAA-CCG
TTG-GTA-CCC-ACA-CCA-TCA-CTG-ACT-TTT-GC
566
fsrCATG-ATT-TTG-TCG-TTA-TTA-GCT-ACT
CAT-CGT-TAA-CAA-CTT-TTT-TAC-TG
1343
Cytolysin operon genescylLLGAT-GGA-GGG-TAA-GAA-TTA-TGG
GCT-TCA-CCT-CAC-TAA-GTT-TTA-TAG
253[117]
cylLsGAA-GCA-CAG-TGC-TAA-ATA-AGG
GTA-TAA-GAG-GGC-TAG-TTT-CAC
240
cylMAAA-AGG-AGT-GCT-TAC-ATG-GAA-GAT
CAT-AAC-CCA-CAC-CAC-TGA-TTC-C
2940
cylBAAG-TAC-ACT-AGT-AGA-ACT-AAG-GGA
ACA-GTG-AAC-GAT-ATA-ACT-CGC-TAT-T
2020
cylAACT-CGG-GGA-TTG-ATA-GGC
GCT-GCT-AAA-GCT-GCG-CTT
688
Enterocin genesentAATG-AAA-CAT-TTA-AAA-ATT-TTG-TCT-ATT-AAA-G
TTA-GCA-CTT-CCC-TGG-AAT-TGC-TCC
1770[118]
entBAGA-CCT-AAC-AAC-TTA-TCT-AAA-G
GTT-GCA-TTT-AGA-GTA-TAC-ATT-TGC
126
entPATG-AGA-AAA-AAA-TTA-TTT-AGT-TTA-GCT-CTT-ATT-GG
TTA-ATG-TCC-CAT-ACC-TGC-CAA-ACC-AG
216
Ef1097GGC-GAT-GGC-ATT-ACT-AAT-GAC-ATT-AGG
CTT-AGC-CCA-CAT-TGA-ACT-GCC-CAT-AAA-GC
408
enlACGA-TTT-CTG-TTG-TAG-GAA-CC
GTA-CAT-CTC-CAT-ATA-CTT-TTC-C
1405
Insertion sequence element geneIS16CATG-TTC-CAG-CAA-CCA-GAG
TCA-AAA-AGT-GGG-CTT-GGC
547[111]
Hyaluronidase genehylACA-GAA-GAG-CTG-CAG-GAA-ATG
GAC-TGA-CGT-CCA-AGT-TTC-CAA
276[119]
Catalase genekatACC-CCG-TAT-CAT-TGG-TTT
ACG-CAT-TGC-TTT-TCC-ATC
419[110]
Lipase geneLip-fmTTG-AGC-TCC-GTT-CCT-GCC-GAA-AGT-CAT-TC
TTG-GTA-CCG-ATT-GGG-GAA-CCA-GAT-TGA-CC
591[108]
Lip-flATG-AGT-GAA-CAA-ATG-GCT-ATT-TA
CTA-AGT-AAG-AAA-TAG-TGC-CTT-GA
740

Table 1.

List of primers reported for the genotypic assessment of major virulence factors.

Table 2.

Illustrations for the PCR conditions for the amplification of various putative virulence genes.

Advertisement

Acknowledgments

The financial support from Higher Education Commission (HEC) Islamabad, Pakistan to SA Ali (HEC No. 20-1339/R&D/09) is greatly acknowledged.

References

  1. 1. Jackson CR, Spicer LM, Barrett JB, Hiott LM. Application of multiplex PCR, pulsed-field gel electrophoresis (PFGE), and BOX-PCR for molecular analysis of enterococci. In: Gel Electrophoresis-Principles and Basics. Rijeka: IntechOpen; 2012
  2. 2. Domig KJ, Mayer HK, Kneifel W. Methods used for the isolation, enumeration, characterisation and identification of Enterococcus spp.: 1. Media for isolation and enumeration. International Journal of Food Microbiology. 2003;88(2-3):147-164
  3. 3. Staley C, Dunny GM, Sadowsky MJ. Environmental and animal-associated enterococci. In: Advances in Applied Microbiology. Jan 1, 2014;87:147-186
  4. 4. Rathnayake IU, Hargreaves M, Huygens F. Antibiotic resistance and virulence traits in clinical and environmental Enterococcus faecalis and Enterococcus faecium isolates. Systematic and Applied Microbiology. 2012;35(5):326-333
  5. 5. Elhani D, Klibi N, Dziri R, Hassan MB, Mohamed SA, Said LB, et al. vanA-containing E. faecium isolates of clonal complex CC17 in clinical and environmental samples in a Tunisian hospital. Diagnostic Microbiology and Infectious Disease. 2014;79(1):60-63
  6. 6. Dadfarma N, Fooladi AA, Oskoui M, Hosseini HM. High level of gentamicin resistance (HLGR) among enterococcus strains isolated from clinical specimens. Journal of Infection and Public Health. 2013;6(3):202-208
  7. 7. Borck Høg B, Korsgaard HB, Wolff Sönksen U, Bager F, Bortolaia V, Ellis-Iversen J, et al. DANMAP 2016 - Use of antimicrobial agents and occurrence of antimicrobial resistance inbacteria from food animals, food and humans in Denmark. Statens Serum Institut, National Veterinary Institute, Technical University of Denmark National Food Institute, Technical University of Denmark; 2017
  8. 8. Hidron AI, Edwards JR, Patel J, Horan TC, Sievert DM, Pollock DA, et al. Antimicrobial-resistant pathogens associated with healthcare-associated infections: Annual summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2006-2007. Infection Control and Hospital Epidemiology. 2008;29(11):996-1011
  9. 9. Gordon S, Swenson JM, Hill BC, Pigott NE, Facklam RR, Cooksey RC, et al. Antimicrobial susceptibility patterns of common and unusual species of enterococci causing infections in the United States. Enterococcal Study Group. Journal of Clinical Microbiology. 1992;30(9):2373-2378
  10. 10. Hoge CW, Adams J, Buchanan B, Sears SD. Enterococcal bacteremia: To treat or not to treat, a reappraisal. Reviews of Infectious Diseases. 1991;13(4):600-605
  11. 11. WHO, Global Priority List of Antibiotic- Resistant Bacteria to Guide Research, Discovery, and Development of New Antibiotics. 2017. Available on-line at: //www.who.int/medicines/publications/global-priority-list-antibiotic-resistant-bacteria/en/
  12. 12. Remschmidt C, Behnke M, Kola A, Diaz LA, Rohde AM, Gastmeier P, et al. The effect of antibiotic use on prevalence of nosocomial vancomycin-resistant enterococci-an ecologic study. Antimicrobial Resistance and Infection Control. 2017;6(1):95
  13. 13. CDC, Antibiotic Resistance Threats in the United States, 2013; Available at: http://www.cdc.gov/drugresistance/threat-report-2013/
  14. 14. Graninger W, Ragette R. Nosocomial bacteremia due to Enterococcus faecalis without endocarditis. Clinical Infectious Diseases. 1992;15(1):49-57
  15. 15. Higuita NI, Huycke MM. Enterococcal disease, epidemiology, and implications for treatment. In: Enterococci: From Commensals to Leading Causes of Drug Resistant Infection [Internet]. Massachusetts Eye and Ear Infirmary; 2014
  16. 16. Noskin GA, Stosor V, Cooper I, Peterson LR. Recovery of vancomycin-resistant enterococci on fingertips and environmental surfaces. Infection Control and Hospital Epidemiology. 1995;16(10):577-581
  17. 17. Patterson JE, Sweeney AH, Simms M, Carley N, Mangi R, Sabetta J, et al. An analysis of 110 serious enterococcal infections. Epidemiology, antibiotic susceptibility, and outcome. Medicine. 1995;74(4):191-200
  18. 18. Rose WE, Rybak MJ. Tigecycline: First of a new class of antimicrobial agents. Pharmacotherapy: The Journal of Human Pharmacology and Drug Therapy. 2006;26(8):1099-1110
  19. 19. Suppli M, Aabenhus R, Harboe ZB, Andersen LP, Tvede M, Jensen JU. Mortality in enterococcal bloodstream infections increases with inappropriate antimicrobial therapy. Clinical Microbiology and Infection. 2011;17(7):1078-1083
  20. 20. National Nosocomial Infections Surveillance (NNIS). System report, data summary from January 1990-May 1999, issued June 1999. American Journal of Infection Control. 1999;27:520-532
  21. 21. Wisplinghoff H, Bischoff T, Tallent SM, Seifert H, Wenzel RP, Edmond MB. Nosocomial bloodstream infections in US hospitals: Analysis of 24,179 cases from a prospective nationwide surveillance study. Clinical Infectious Diseases. 2004;39(3):309-317
  22. 22. Schønheyder HC, Søgaard M. Hospital-acquired bacteraemia and fungaemia. A regional study with national implications. Ugeskrift for Laeger. 2007;169(48):4175-4179
  23. 23. Bryan CS, Reynolds KL, Brown JJ. Mortality associated with enterococcal bacteremia. Surgery, Gynecology & Obstetrics. 1985;160(6):557-561
  24. 24. Lautenbach E, Bilker WB, Brennan PJ. Enterococcal bacteremia: Risk factors for vancomycin resistance and predictors of mortality. Infection Control and Hospital Epidemiology. 1999;20(5):318-323
  25. 25. Vergis EN, Hayden MK, Chow JW, Snydman DR, Zervos MJ, Linden PK, et al. Determinants of vancomycin resistance and mortality rates in enterococcal bacteremia: A prospective multicenter study. Annals of Internal Medicine. 2001;135(7):484-492
  26. 26. Vergis EN, Shankar N, Chow JW, Hayden MK, Snydman DR, Zervos MJ, et al. Association between the presence of enterococcal virulence factors gelatinase, hemolysin, and enterococcal surface protein and mortality among patients with bacteremia due to Enterococcus faecalis. Clinical Infectious Diseases. 2002;35(5):570-575
  27. 27. MacCallum WG, Hastings TW. A case of acute endocarditis caused by Micrococcus zymogenes (Nov. Spec.), with a description of the microorganism. The Journal of Experimental Medicine. 1899;4(5-6):521-534
  28. 28. Bouza E, Menasalvas A, Munoz P, Vasallo FJ, Moreno MD, Fernandez MA. Infective endocarditis—A prospective study at the end of the twentieth century: New predisposing conditions, new etiologic agents, and still a high mortality. Medicine. 2001;80(5):298-307
  29. 29. Murdoch DR, Corey GR, Hoen B, Miró JM, Fowler VG, Bayer AS, et al. Clinical presentation, etiology, and outcome of infective endocarditis in the 21st century: The international collaboration on endocarditis–prospective cohort study. Archives of Internal Medicine. 2009;169(5):463-473
  30. 30. Dahl A, Rasmussen RV, Bundgaard H, Hassager C, Bruun LE, Lauridsen TK, et al. Enterococcus faecalis infective endocarditis: A pilot study of the relationship between duration of gentamicin treatment and outcome. Circulation. 2013;127(17):1810-1817
  31. 31. Anderson DJ, Murdoch DR, Sexton DJ, Reller LB, Stout JE, Cabell CH, et al. Risk factors for infective endocarditis in patients with enterococcal bacteremia: A case-control study. Infection. 2004;32(2):72-77
  32. 32. McDonald JR, Olaison L, Anderson DJ, Hoen B, Miro JM, Eykyn S, et al. Enterococcal endocarditis: 107 cases from the international collaboration on endocarditis merged database. The American Journal of Medicine. 2005;118(7):759-766
  33. 33. Galloway-Peña J, Roh JH, Latorre M, Qin X, Murray BE. Genomic and SNP analyses demonstrate a distant separation of the hospital and community-associated clades of Enterococcus faecium. PLoS One. 2012;7(1):e30187
  34. 34. Palmer KL, Godfrey P, Griggs A, Kos VN, Zucker J, Desjardins C, et al. Comparative genomics of enterococci: Variation in Enterococcus faecalis, clade structure in E. faecium, and defining characteristics of E. gallinarum and E. casseliflavus. MBio. 2012;3(1):e00318-e00311
  35. 35. Baddour LM, Wilson WR, Bayer AS, Fowler VG Jr, Bolger AF, Levison ME, et al. Infective endocarditis: diagnosis, antimicrobial therapy, and management of complications: a statement for healthcare professionals from the Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease, Council on Cardiovascular Disease in the Young, and the Councils on Clinical Cardiology, Stroke, and Cardiovascular Surgery and Anesthesia, American Heart Association: endorsed by the Infectious Diseases Society of America. Circulation. 2005;111(23):e394-e434
  36. 36. Matsumura S, Simor AE. Treatment of endocarditis due to vancomycin-resistant Enterococcus faecium with quinupristin/dalfopristin, doxycycline, and rifampin: A synergistic drug combination. Clinical Infectious Diseases. Dec 1, 1998;27(6):1554-1556
  37. 37. Bethea JA, Walko CM, Targos PA. Treatment of vancomycin-resistant enterococcus with quinupristin/dalfopristin and high-dose ampicillin. The Annals of Pharmacotherapy. 2004;38(6):989-991
  38. 38. Schlievert PM, Chuang-Smith ON, Peterson ML, Cook LC, Dunny GM. Enterococcus faecalis endocarditis severity in rabbits is reduced by IgG Fabs interfering with aggregation substance. PLoS One. 2010;5(10):e13194
  39. 39. Singh KV, Nallapareddy SR, Sillanpää J, Murray BE. Importance of the collagen adhesin ace in pathogenesis and protection against Enterococcus faecalis experimental endocarditis. PLoS Pathogens. 2010;6(1):e1000716
  40. 40. Nallapareddy SR, Singh KV, Murray BE. Contribution of the collagen adhesin Acm to pathogenesis of Enterococcus faecium in experimental endocarditis. Infection and Immunity. 2008;76(9):4120-4128
  41. 41. Heikens E, Bonten MJ, Willems RJ. Enterococcal surface protein Esp is important for biofilm formation of Enterococcus faecium E1162. Journal of Bacteriology. 2007;189(22):8233-8240
  42. 42. Heikens E, Singh KV, Jacques-Palaz KD, van Luit-Asbroek M, Oostdijk EA, Bonten MJ, et al. Contribution of the enterococcal surface protein Esp to pathogenesis of Enterococcus faecium endocarditis. Microbes and Infection. 2011;13(14-15):1185-1190
  43. 43. Kemp KD, Singh KV, Nallapareddy SR, Murray BE. Relative contributions of Enterococcus faecalis OG1RF sortase-encoding genes, srtA and bps (srtC), to biofilm formation and a murine model of urinary tract infection. Infection and Immunity. 2007;75(11):5399-5404
  44. 44. Nallapareddy SR, Singh KV, Sillanpää J, Zhao M, Murray BE. Relative contributions of Ebp Pili and the collagen adhesin ace to host extracellular matrix protein adherence and experimental urinary tract infection by Enterococcus faecalis OG1RF. Infection and Immunity. 2011;79(7):2901-2910
  45. 45. Munita JM, Arias CA, Murray BE. Enterococcal endocarditis: Can we win the war? Current Infectious Disease Reports. 2012;14(4):339-349
  46. 46. Chajęcka-Wierzchowska W, Zadernowska A, Łaniewska-Trokenheim Ł. Virulence factors of Enterococcus spp. presented in food. LWT. 2017;75:670-676
  47. 47. Mohamed JA, Huang DB. Biofilm formation by enterococci. Journal of Medical Microbiology. 2007;56(12):1581-1588
  48. 48. Singh KV, Qin X, Weinstock GM, Murray BE. Generation and testing of mutants of Enterococcus faecalis in a mouse peritonitis model. The Journal of Infectious Diseases. 1998;178(5):1416-1420
  49. 49. Singh KV, Nallapareddy SR, Nannini EC, Murray BE. Fsr-independent production of protease (s) may explain the lack of attenuation of an Enterococcus faecalis fsr mutant versus a gelE-sprE mutant in induction of endocarditis. Infection and Immunity. 2005;73(8):4888-4894
  50. 50. Engelbert M, Mylonakis E, Ausubel FM, Calderwood SB, Gilmore MS. Contribution of gelatinase, serine protease, and fsr to the pathogenesis of Enterococcus faecalis endophthalmitis. Infection and Immunity. 2004;72(6):3628-3633
  51. 51. Sifri CD, Mylonakis E, Singh KV, Qin X, Garsin DA, Murray BE, et al. Virulence effect of Enterococcus faecalis protease genes and the quorum-sensing locus fsr in Caenorhabditis elegans and mice. Infection and Immunity. 2002;70(10):5647-5650
  52. 52. Zeng J, Teng F, Murray BE. Gelatinase is important for translocation of Enterococcus faecalis across polarized human enterocyte-like T84 cells. Infection and Immunity. 2005;73(3):1606-1612
  53. 53. Qin X, Singh KV, Weinstock GM, Murray BE. Characterization of fsr, a regulator controlling expression of gelatinase and serine protease in Enterococcus faecalis OG1RF. Journal of Bacteriology. 2001;183(11):3372-3382
  54. 54. Qin X, Singh KV, Weinstock GM, Murray BE. Effects of Enterococcus faecalis fsr genes on production of gelatinase and a serine protease and virulence. Infection and Immunity. 2000;68(5):2579-2586
  55. 55. Nakayama J, Cao Y, Horii T, Sakuda S, Akkermans AD, De Vos WM, et al. Gelatinase biosynthesis-activating pheromone: A peptide lactone that mediates a quorum sensing in Enterococcus faecalis. Molecular Microbiology. 2001;41(1):145-154
  56. 56. Sava IG, Heikens E, Huebner J. Pathogenesis and immunity in enterococcal infections. Clinical Microbiology and Infection. 2010;16(6):533-540
  57. 57. Coque TM, Patterson JE, Steckelberg JM, Murray BE. Incidence of hemolysin, gelatinase, and aggregation substance among enterococci isolated from patients with endocarditis and other infections and from feces of hospitalized and community-based persons. The Journal of Infectious Diseases. 1995;171(5):1223-1229
  58. 58. Garsin DA, Sifri CD, Mylonakis E, Qin X, Singh KV, Murray BE, et al. A simple model host for identifying gram-positive virulence factors. Proceedings of the National Academy of Sciences USA. 2001;98(19):10892-10897
  59. 59. Håkansson KO, Brugna M, Tasse L. The three-dimensional structure of catalase from Enterococcus faecalis. Acta Crystallographica, Section D: Biological Crystallography. 2004;60(8):1374-1380
  60. 60. Zamocky M, Furtmüller PG, Obinger C. Evolution of catalases from bacteria to humans. Antioxidants & Redox Signaling. 2008;10(9):1527-1548
  61. 61. Frankenberg L, Brugna M, Hederstedt L. Enterococcus faecalis heme-dependent catalase. Journal of Bacteriology. 2002;184(22):6351-6356
  62. 62. Baureder M, Hederstedt L. Genes important for catalase activity in Enterococcus faecalis. PLoS One. 2012;7(5):e36725
  63. 63. Hynes WL, Walton SL. Hyaluronidases of gram-positive bacteria. FEMS Microbiology Letters. 2000;183(2):201-207
  64. 64. Arias CA, Panesso D, Singh KV, Rice LB, Murray BE. Cotransfer of antibiotic resistance genes and a hylEfm-containing virulence plasmid in Enterococcus faecium. Antimicrobial Agents and Chemotherapy. 2009;53(10):4240-4246
  65. 65. Rice LB, Laktičova V, Carias LL, Rudin S, Hutton R, Marshall SH. Transferable capacity for gastrointestinal colonization in Enterococcus faecium in a mouse model. The Journal of Infectious Diseases. 2009;199(3):342-349
  66. 66. Garsin DA, Frank KL, Silanpää J, Ausubel FM, Hartke A, Shankar N, et al. Pathogenesis and models of enterococcal infection. In: Enterococci: From Commensals to Leading Causes of Drug Resistant Infection [Internet]. Massachusetts Eye and Ear Infirmary; 2014
  67. 67. Panesso D, Montealegre MC, Rincón S, Mojica MF, Rice LB, Singh KV, et al. The hyl Efm gene in pHyl Efm of Enterococcus faecium is not required in pathogenesis of murine peritonitis. BMC Microbiology. 2011;11(1):20
  68. 68. Van Tyne D, Martin M, Gilmore M. Structure, function, and biology of the Enterococcus faecalis cytolysin. Toxins. 2013;5(5):895-911
  69. 69. Shankar N, Baghdayan AS, Gilmore MS. Modulation of virulence within a pathogenicity island in vancomycin-resistant Enterococcus faecalis. Nature. 2002;417(6890):746
  70. 70. Haas W, Shepard BD, Gilmore MS. Two-component regulator of Enterococcus faecalis cytolysin responds to quorum-sensing autoinduction. Nature. 2002;415(6867):84
  71. 71. Tendolkar PM, Baghdayan AS, Shankar N. Pathogenic enterococci: New developments in the 21st century. Cellular and Molecular Life Sciences: CMLS. 2003;60(12):2622-2636
  72. 72. Clewell DB. Bacterial sex pheromone-induced plasmid transfer. Cell. 1993;73:9-12
  73. 73. Ike YA, Clewell DB. Evidence that the hemolysin/bacteriocin phenotype of Enterococcus faecalis subsp. zymogenes can be determined by plasmids in different incompatibility groups as well as by the chromosome. Journal of Bacteriology. 1992;174(24):8172-8177
  74. 74. Süßmuth SD, Muscholl-Silberhorn A, Wirth R, Susa M, Marre R, Rozdzinski E. Aggregation substance promotes adherence, phagocytosis, and intracellular survival of Enterococcus faecalis within human macrophages and suppresses respiratory burst. Infection and Immunity. 2000;68(9):4900-4906
  75. 75. Todd EW. A comparative serological study of streptolysins derived from human and from animal infections, with notes on pneumococcal haemolysin, tetanolysin and staphylococcus toxin. The Journal of Pathology and Bacteriology. 1934;39:299-321
  76. 76. Ike Y, Hashimoto H, Clewell DB. Hemolysin of Streptococcus faecalis subspecies zymogenes contributes to virulence in mice. Infection and Immunity. 1984;45(2):528-530
  77. 77. Jett BD, Jensen HG, Nordquist RE, Gilmore MS. Contribution of the pAD1-encoded cytolysin to the severity of experimental Enterococcus faecalis endophthalmitis. Infection and Immunity. 1992;60(6):2445-2452
  78. 78. Miyazaki S, Ohno A, Kobayashi I, Uji T, Yamaguchi K, Goto S. Cytotoxic effect of hemolytic culture supernatant from Enterococcus faecalis on mouse polymorphonuclear neutrophils and macrophages. Microbiology and Immunology. 1993;37(4):265-270
  79. 79. Schlievert PM, Gahr PJ, Assimacopoulos AP, Dinges MM, Stoehr JA, Harmala JW, Hirt H, Dunny GM. Aggregation and binding substances enhance pathogenicity in rabbit models of Enterococcus faecalis endocarditis. Infection and Immunity. Jan 1, 1998;66(1):218-223
  80. 80. Stevens SX, Jensen HG, Jett BD, Gilmore MS. A hemolysin-encoding plasmid contributes to bacterial virulence in experimental Enterococcus faecalis endophthalmitis. Investigative Ophthalmology & Visual Science. 1992;33(5):1650-1656
  81. 81. Stein T, Heinzmann S, Solovieva I, Entian KD. Function of Lactococcus lactis nisin immunity genes nisI and nisFEG after coordinated expression in the surrogate host Bacillus subtilis. The Journal of Biological Chemistry. 2003;278(1):89-94
  82. 82. Stein T, Heinzmann S, Düsterhus S, Borchert S, Entian KD. Expression and functional analysis of the subtilin immunity genes spaIFEG in the subtilin-sensitive host Bacillus subtilis MO1099. Journal of Bacteriology. 2005;187(3):822-828
  83. 83. Coburn PS, Hancock LE, Booth MC, Gilmore MS. A novel means of self-protection, unrelated to toxin activation, confers immunity to the bactericidal effects of the Enterococcus faecalis cytolysin. Infection and Immunity. 1999;67(7):3339-3347
  84. 84. Bassler BL, Losick R. Bacterially speaking. Cell. 2006;125(2):237-246
  85. 85. Roux A, Payne SM, Gilmore MS. Microbial telesensing: Probing the environment for friends, foes, and food. Cell Host & Microbe. 2009;6(2):115-124
  86. 86. Wästfelt M, Stålhammar-Carlemalm M, Delisse AM, Cabezon T, Lindahl G. Identification of a family of streptococcal surface proteins with extremely repetitive structure. The Journal of Biological Chemistry. 1996;271(31):18892-18897
  87. 87. Cucarella C, Solano C, Valle J, Amorena B, Lasa Í, Penadés JR. Bap, a Staphylococcus aureus surface protein involved in biofilm formation. Journal of Bacteriology. 2001;183(9):2888-2896
  88. 88. Keane PF, Bonner MC, Johnston SR, Zafar A, Gorman SP. Characterization of biofilm and encrustation on ureteric stents in vivo. British Journal of Urology. 1994;73(6):687-691
  89. 89. Sandoe JA, Witherden IR, Cove JH, Heritage J, Wilcox MH. Correlation between enterococcal biofilm formation in vitro and medical-device-related infection potential in vivo. Journal of Medical Microbiology. 2003;52(7):547-550
  90. 90. Dautle MP, Wilkinson TR, Gauderer MW. Isolation and identification of biofilm microorganisms from silicone gastrostomy devices. Journal of Pediatric Surgery. 2003;38(2):216-220
  91. 91. Dowidar N, Moesgaard F, Matzen P. Clogging and other complications of endoscopic biliary endoprostheses. Scandinavian Journal of Gastroenterology. 1991;26(11):1132-1136
  92. 92. Eaton TJ, Gasson MJ. Molecular screening of Enterococcus virulence determinants and potential for genetic exchange between food and medical isolates. Applied and Environmental Microbiology. 2001;67(4):1628-1635
  93. 93. Willems RJ, Homan W, Top J, van Santen-Verheuvel M, Tribe D, Manzioros X, et al. Variant esp gene as a marker of a distinct genetic lineage of vancomycin-resistant Enterococcus faecium spreading in hospitals. The Lancet. 2001;357(9259):853-855
  94. 94. Leavis H, Top J, Shankar N, Borgen K, Bonten M, van Embden J, et al. A novel putative enterococcal pathogenicity island linked to the esp virulence gene of Enterococcus faecium and associated with epidemicity. Journal of Bacteriology. 2004;186(3):672-682
  95. 95. Leendertse M, Heikens E, Wijnands LM, van Luit-Asbroek M, Teske GJ, Roelofs JJ, et al. Enterococcal surface protein transiently aggravates Enterococcus faecium–induced urinary tract infection in mice. The Journal of Infectious Diseases. 2009;200(7):1162-1165
  96. 96. Heikens E, Leendertse M, Wijnands LM, van Luit-Asbroek M, Bonten MJ, van der Poll T, et al. Enterococcal surface protein Esp is not essential for cell adhesion and intestinal colonization of Enterococcus faecium in mice. BMC Microbiology. 2009;9(1):19
  97. 97. Tendolkar PM, Baghdayan AS, Gilmore MS, Shankar N. Enterococcal surface protein, Esp, enhances biofilm formation by Enterococcus faecalis. Infection and Immunity. 2004;72(10):6032-6039
  98. 98. Dworniczek E, Wojciech L, Sobieszczanska B, Seniuk A. Virulence of enterococcus isolates collected in lower Silesia (Poland). Scandinavian Journal of Infectious Diseases. 2005;37(9):630-636
  99. 99. Ramadhan AA, Hegedus E. Biofilm formation and esp gene carriage in enterococci. Journal of Clinical Pathology. 2005;58(7):685-686
  100. 100. Kristich CJ, Li YH, Cvitkovitch DG, Dunny GM. Esp-independent biofilm formation by Enterococcus faecalis. Journal of Bacteriology. 2004;186(1):154-163
  101. 101. Mohamed JA, Huang W, Nallapareddy SR, Teng F, Murray BE. Influence of origin of isolates, especially endocarditis isolates, and various genes on biofilm formation by Enterococcus faecalis. Infection and Immunity. 2004;72(6):3658-3663
  102. 102. Kreft Á, Marre R, Schramm U, Wirth R. Aggregation substance of Enterococcus faecalis mediates adhesion to cultured renal tubular cells. Infection and Immunity. 1992;60(1):25-30
  103. 103. Vanek NN, Simon SI, Jacques-Palaz K, Mariscalco MM, Dunny GM, Rakita RM. Enterococcus faecalis aggregation substance promotes opsonin independent binding to human neutrophils via a complement receptor type 3-mediated mechanism. FEMS Immunology and Medical Microbiology. 1999;26(1):49-60
  104. 104. Waters CM, Hirt H, McCormick JK, Schlievert PM, Wells CL, Dunny GM. An amino-terminal domain of Enterococcus faecalis aggregation substance is required for aggregation, bacterial internalization by epithelial cells and binding to lipoteichoic acid. Molecular Microbiology. 2004;52(4):1159-1171
  105. 105. Rakita RM, Vanek NN, Jacques-Palaz K, Mee M, Mariscalco MM, Dunny GM, et al. Enterococcus faecalis bearing aggregation substance is resistant to killing by human neutrophils despite phagocytosis and neutrophil activation. Infection and Immunity. 1999;67(11):6067-6075
  106. 106. Schlievert PM, Gahr PJ, Assimacopoulos AP, Dinges MM, Stoehr JA, Harmala JW, et al. Aggregation and binding substances enhance pathogenicity in rabbit models of Enterococcus faecalis endocarditis. Infection and Immunity. 1998;66(1):218-223
  107. 107. Ali SA, Hasan KA, Bin Asif H, Abbasi A. Environmental enterococci: I. prevalence of virulence, antibiotic resistance and species distribution in poultry and its related environment in Karachi, Pakistan. Letters in Applied Microbiology. 2014;58(5):423-432
  108. 108. Ali SA, Bin-Asif H, Hasan KA, Rehman M, Abbasi A. Molecular assessment of virulence determinants, hospital associated marker (IS16gene) and prevalence of antibiotic resistance in soil borne Enterococcus species. Microbial Pathogenesis. 2017;105:298-306
  109. 109. Zahid S, Bin-Asif H, Hasan KA, Rehman M, Ali SA. Prevalence and genetic profiling of tetracycline resistance (Tet-R) genes and transposable element (Tn916) in environmental Enterococcus species. Microbial Pathogenesis. 2017;111:252-261
  110. 110. Hasan KA, Ali SA, Rehman M, Bin-Asif H, Zahid S. The unravelled Enterococcus faecalis zoonotic superbugs: Emerging multiple resistant and virulent lineages isolated from poultry environment. Zoonoses and Public Health. 2018;65(8):921-935
  111. 111. Werner G, Fleige C, Geringer U, van Schaik W, Klare I, Witte W. IS element IS16 as a molecular screening tool to identify hospital-associated strains of Enterococcus faecium. BMC Infectious Diseases. 2011;11(1):80
  112. 112. Lanthier M, Scott A, Lapen DR, Zhang Y, Topp E. Frequency of virulence genes and antibiotic resistances in Enterococcus spp. isolates from wastewater and feces of domesticated mammals and birds, and wildlife. Canadian Journal of Microbiology. 2010;56(9):715-729
  113. 113. Camargo IL, Gilmore MS, Darini AL. Multilocus sequence typing and analysis of putative virulence factors in vancomycin-resistant and vancomycin-sensitive Enterococcus faecium isolates from Brazil. Clinical Microbiology and Infection. 2006;12(11):1123-1130
  114. 114. Biendo M, Adjide C, Castelain S, Belmekki M, Rousseau F, Slama M, et al. International Journal of Microbiology. 2010;2010:150464
  115. 115. Duprè I, Zanetti S, Schito AM, Fadda G, Sechi LA. Incidence of virulence determinants in clinical Enterococcus faecium and Enterococcus faecalis isolates collected in Sardinia (Italy). Journal of Medical Microbiology. 2003;52(6):491-498
  116. 116. Lopes MD, Simões AP, Tenreiro R, Marques JJ, Crespo MT. Activity and expression of a virulence factor, gelatinase, in dairy enterococci. International Journal of Food Microbiology. 2006;112(3):208-214
  117. 117. Semedo T, Santos MA, Martins P, Lopes MF, Marques JJ, Tenreiro R, et al. Comparative study using type strains and clinical and food isolates to examine hemolytic activity and occurrence of the cyl operon in enterococci. Journal of Clinical Microbiology. 2003;41(6):2569-2576
  118. 118. Almeida T, Brandão A, Muñoz-Atienza E, Goncalves A, Torres C, Igrejas G, et al. Identification of bacteriocin genes in enterococci isolated from game animals and saltwater fish. Journal of Food Protection. 2011;74(8):1252-1260
  119. 119. Iweriebor BC, Gaqavu S, Obi LC, Nwodo UU, Okoh AI. Antibiotic susceptibilities of Enterococcus species isolated from hospital and domestic wastewater effluents in Alice, Eastern Cape Province of South Africa. International Journal of Environmental Research and Public Health. 2015;12(4):4231-4246

Written By

Hassan Bin-Asif and Syed Abid Ali

Submitted: 16 April 2019 Reviewed: 08 August 2019 Published: 29 October 2019