Over the years, numerous studies have been conducted into the possible links between biofilms in beverage industry and health safety. Consumers trust that the soft drinks they buy are safe and their quality is guaranteed. This chapter provides an overview of available scientific knowledge and cites numerous studies on various aspects of biofilms in drinking water technology and soft drinks industry and their implications for health safety. Particular attention is given to Proteobacteria, including two different genera: Aeromonas, which represents Gammaproteobacteria, and Asaia, a member of Alphaproteobacteria.
- soft drinks
1. Drinking water systems
In water systems, both natural and industrial dominate
Although bacteria are physiologically and morphologically diverse, they constitute a coherent set of six main classes:
In natural systems, freshwater or potable water distribution networks,
One of the common features of
A first step in the successional development of biofilms is the coating of uncolonized surfaces with many particles, organic or inorganic (conditioning film), which enhances attachment of initial colonizing bacteria. Anything that may be present within the bulk fluid can through gravitational force or movement of flow settle onto a surface and become part of a conditioning layer. Surface charge, potential, and tensions can be altered favorably by the interactions between the conditioning layer and the surface. Factors such as available energy, surface functionality, bacterial orientation, temperature and pressure conditions are local environmental variables which contribute to bacterial adhesion. Physical forces associated to bacterial adhesion include the van der Waals’ forces, steric interactions, and electrostatic (double layer) interactions, collectively known as the DVLO (Derjaguin, Verwey, Landau, and Overbeek) forces . An extended DVLO theory takes into consideration hydrophobic/hydrophilic and osmotic interactions.
In real time, a number of the reversibly adsorbed cells remain immobilized and become irreversibly adsorbed. The physical appendages of bacteria (flagella, fimbriae, and pili) overcome the physical repulsive forces of the electrical double layer. Some evidence has shown that microbial adhesion strongly depends on the hydrophobic–hydrophilic properties of interacting surfaces. The first colonizers grow in surface-attached microcolonies and produce EPS. After an initial lag phase, a rapid increase in population is observed, which is described as the exponential growth phase. As the microcolonies develop, additional species, the so-called secondary colonizers, are recruited through coaggregation and nonspecific aggregation interactions, increasing the biofilm biomass and species complexity .
Simultaneously, expression of a number of genes for the production of cell surface proteins and excretion products increases. Surface proteins (porins) such as Opr C and Opr E allow the transport of extracellular products into the cell and excretion materials out of the cell, e.g., polysaccharides. EPS molecules impart mechanical stability and are pivotal to biofilm adhesion and cohesion, and evasion from harsh dynamic environmental conditions. The differences in gene expression of planktonic and sessile cells were identified, and as many as 57 biofilm-associated proteins were not found in the planktonic profile .
Physicochemical nature of such consortia implies differentiation of the physiological condition of individuals forming them . Creating consortium is an effective adaptation strategy, including cell protection against adverse environmental factors; increased nutrient availability; increased binding of water molecules, thereby reducing the risk of dehydration; and increased ability to transfer DNA.
Microbial consortia exhibit altered phenotypic characteristics compared to planktonic cells, particularly with respect to growth and gene expression. All these factors increase the survival of cells forming biofilms. As a result, the inactivation of bacterial cells by conventional methods such as the use of antibiotics and disinfectants is often ineffective . Especially this exopolymer matrix confers resistant properties to the whole system via the limitation of the effectiveness of disinfection by consuming the oxidants used, such as chlorine and chloramines .
At high cell concentration, a series of cell signaling mechanisms are employed by the biofilm, and this is collectively termed
Biofilms are polymicrobial communities, therefore the potential for cell coaggregation plays an integral role in spatiotemporal biofilm development and the moderation of biofilm composition. Coaggregation is mediated by the interaction between specific macromolecules on the cell surface of one species and cognate macromolecules expressed on the cell surface of the partner species. Microbial cells may also come into contact through hydrophobic interactions or electrostatic forces, but these last associations are relatively weak. Coaggregation-mediating proteins are referred as adhesins. Coaggregation may occur between lectin-like protein adhesins and their polysaccharide receptors or by protein–protein (adhesin–adhesin) interactions. These interactions may be unimodal, but in some cases are bimodal, involving two different interacting pairs of macromolecules .
Cell aggregation, as well as biofilm formation may have both intrageneric and intergeneric character . Consortia are very changeable and their components depend on the environmental conditions. The study conducted by Rickard et al.  revealed that intergeneric and intraspecies coaggregation between water bacteria are common phenomena, and expression of coaggregation is dependent on cells being in the optimum physiological state for coaggregation, which usually occurs in stationary phase. Therefore, it is possible that since cells grow very slowly in nutrient-limited biofilms, these biofilms would provide suitable conditions for expression of coaggregation.
Different materials such as cast iron galvanized steel, stainless steel, copper, and polyethylene are used to manufacture water distribution pipes. It is worth noting that these materials favor biofilm formation in the water distribution systems. The presence of biofilms in drinking water distribution pipes usually leads to a number of undesirable effects on the quality of water that is supplied to consumers. For example, the development of biofilms in copper pipes facilitates cuprosolvency which increases the release of copper into the distribution system. What's more, increased carbon influences the growth of heterotrophic plate count bacteria which are also involved in the corrosion of copper . Silhan et al.  showed that among drinking water pipe materials such as galvanized steel, cross-linked polyethylene, copper pipes, and medium-density polyethylene, the most dense biofilm of
Molecular analysis of microbial communities by Yu et al.  indicated the presence of
The development of biofilms inside water distribution pipes facilitates the propagation of mixed microbial populations and is considered the main source of planktonic bacteria in water supply systems. Among the heterotrophic bacteria in drinking water systems, the pathogenic bacteria or at least opportunistic pathogens often appear. Enteropathogenic
In the last decade, a group of new, potentially dangerous pathogens forming biofilms were classified as
According to Sautour et al. , the genus
It was noted that there was an intense increase in the number of heterotrophic bacteria in the summer months. The results obtained by Craveiro et al.  demonstrated that
The vast majority of bacteria isolated from biofilms belonged to
In clinical and environmental isolates of
In studies conducted by Kregiel et al.,
The studies have found that both due to the strong adhesive properties of
2. Soft drinks
When a change in the chemical nature of a fluid occurred, there is usually a qualitative shift created microbial consortia . While the succession is a well-known process in classical ecology, in the case of biofilms or cell aggregates it is not fully understood. Despite many researches, the full knowledge on the formation of microbial consortia is still lacking. However, succession processes seem to be rather stochastic (reproduction and death) . During growth of consortia, competition for resources makes that weak individuals are eliminated, and stronger competitors become dominant. Finally, in the mature consortia, cells are becoming more diverse by individual differences and “internal recycling.”
Environmental factors may also shape the succession in microbial consortia. Changes in pH, the presence of carbon sources in the form of saccharides, and other additional substances cause significant qualitative changes in biofilms .
For example, the flavored drinking water samples with sucrose and natural fruit flavors showing signs of turbidity and the characteristic "flocs" formed by heterotrophic bacteria . The developed specific methods allowed for the isolation of bacteria belonging to the
It was found that the hydrophobicity of the cells decreased with increasing the age of the population. The higher hydrophobicity of young cells stimulates the process of aggregation and formation of flocs. The studies proved that the adhesive abilities of
Definitely, the level of cell adhesion decreased in media that is rich in nutrients. Biofilm creation in a specific medium which was the commercial mineral flavored water had a dynamic character .
It is difficult to determine the origin of the contamination of soft drinks with the
The resistance of
3. New antiadhesion strategy: organosilanes
It is known that it is best to prevent than to fight against biofilm formed on the internal surface of a distribution system. For drinking waters and soft drinks, reduction or elimination of the formation of cell consortia can be obtained only by changing the physicochemical properties of abiotic surfaces or bioactive properties of consumption waters.
Compounds of the biocidal and/or antiadhesive properties applied in potable water systems have to inhibit effectively the growth of microorganisms without releasing toxic compounds with low molecular weight into aquatic environment. Such compounds may be organosilanes containing at least one bond between the carbon and silicon atom Si–CH3. A carbon–silicon bond is very durable, and the presence of an alkyl group causes a change in surface tension. Additionally, organosilanes can contain other functional groups with antimicrobial properties, for example, methoxy, ethoxy, amino, methacrylic, and sulfide .
Organofunctional silanes are hybrid compounds that combine the functionality of a reactive organic group and the inorganic functionality of an alkyl silicate in a single molecule. This special property means they can be used as ‘molecular bridges’ between organic substrates and inorganic materials (Figure 4).
These compounds are relatively environmentally friendly, improve adhesion, and provide better protection against corrosion. Surfaces on which they can be used include metal, plastic, glass, rubber, ceramic, porcelain, marble, cement, granite, tile, silica, sand, appliances that have been enameled, polyester, polyurethane, polyacrylic, resins that are melamine or phenolic, siliceous, polycarbonate and wood, as well as painted surfaces.
The growth of many microorganisms can be reduced on surfaces treated with alkylsilanes. In general, the reactivity of hydroxylated surfaces with organofunctional silanes decreases in the following order: Si–NR2 > Si–Cl > Si–NH–Si > Si–O2CCH3 > Si–OCH3 > Si–OCH2CH3. The methoxy and ethoxysilanes are the most widely used organofunctional silanes for surface modification. The methoxysilanes are capable of reacting with substrates under dry, protic conditions, while the less reactive ethoxysilanes require catalysis. The low toxicity of ethanol, a byproduct of the reaction, favors the use of ethoxysilanes in many commercial applications .
One of the most established and successful uses of the application of organosilanes is prevention against biofilm formation. The use of the proper quaternary amine-based organosilane can provide durable antimicrobial protection against a wide variety of microorganisms .
Adhesion abilities of
4. New antiadhesion strategy: proanthocyanidins
Scientific studies showed that natural compounds from different fruits have potential health benefits against cancer, aging and neurological diseases, inflammation, diabetes, and bacterial infections. For example, cranberry juice was recognized for benefits of maintenance of a healthy urinary tract. Cranberry is a term derived from the contraction of “crane berry.” This name is derived from the nickname of the bilberry flower, and the sand crane, a bird that often feeds on the berries of this plant. The cranberry is part of the
Bacterial adhesion is accomplished by the binding of lectins exposed on the cell surfaces of pili and fimbriae to complementary carbohydrates on the host tissues. Pili are small filaments that can be either mannose-resistant or mannose-sensitive. The mannose-sensitive pili, called type 1 pili, permit bacterial adhesion to the urothelium. The fimbriae (p-fimbriae) are inhibited by fructose, present in cranberries. The more virulent strains of
The current hypothesis is that cranberries work principally by preventing the adhesion of type 1 and p-fimbriae
Proanthocyanidins are one of many plant phenols, which are aromatic secondary metabolites found in the plant kingdom. They are mainly found in
They are also known as olgoflavanoids, and consist of monomer flavan-3-ol units. When linked through either C4 to C8 or C4 to C6 bonds, the linkages are called B-linked. When the linkages were through a C2 and C7 compound, they are called A type . While B-linked proanthocyanidins can be found in different fruit products including apple juice, purple grape juice, green tea, and dark chocolate, A-linked ones are found in cranberries and it is a linkage with unique antiadhesion properties associated with them  (Figure 5).
The antiadhesive properties of cranberry were demonstrated against different microorganisms:
It was also noted that the adhesion of
Problems related to microbial contamination in the beverage industry have been studied for more than a century. However, most of the knowledge acquired over the years relates to single-cells, but today it is generally accepted that microorganisms grow and survive in organized communities where their physiology is very different. This paper has given an overview of the most widely used research on the controlled attachment of specific bacteria present in drinking water or soft drinks. Both surfaces modified by organosilanes and cranberry juice supplementation are the latest developments in this area. Particularly, cranberry juice and cranberry extracts may be investigated as a natural solution for food industry by creating an additional barrier to inhibit the growth of spoilage bacteria and providing additional health benefits.
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