Biofilms-Associated Infections Continuous Challenges in Human and Animal Health

Abstract

Biofilms can be defined as a structured consortium of microbial cells surrounded by the self-produced matrix (Figure 17.1) (Høiby 2017). Biofilms is known to be produced by many of bacteria including the important pathogen that cause life-threatening infections in humans and animals such as Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter spp., Salmonella spp., Escherichia coli, etc. (Tasneem et al. 2018). These bacteria are known to cause a serious problem in human and animal health (Jamal et al. 2018; Abdullahi et al. 2016). Structurally, the biofilms is built of individual (planktonic) bacterial cells attached with the self-released lipopolysaccharides, proteins, lipids, glycolipids, and nucleic acids. These components are recognized as extra-polymeric substances (EPSs). The EPS is responsible to promote adhesion and aggregation of bacteria to the surfaces and provides stability to the biofilms structure (Kamaruzzaman et al. 2018). The lipopolysaccharide produced by the bacteria is different from the bacteria species. For example, P. aeruginosa produces Pel (a cationic exopolysaccharide composed of 1–4 linked galactosamine and glucosamine sugars) and Psl (a pentasaccharide composed of D-glucose, D-mannose, and L-rhamnose) (Billings et al. 2013; Jennings et al. 2015) while S. aureus and Staphylococcus epidermidis produce poly-ß(1,6)- N-acetyl-D-glucosamine (PNAG) (Izano et al. 2008). The nucleic acid is known as extracellular DNA (eDNA) that interacts with extracellular calcium (Ca2+) within the biofilms structure to induce bacterial aggregation via cationic bridging. The positive charge of Ca2+ repulses the negative charge of the biofilms’s component, thus assisting the adherence of the biofilms to the material and tissue surface. The negatively charged eDNA chelates the action of cationic antimicrobial peptides of the immune system, thus acting as the defense mechanism to the structure (Okshevsky, Regina, and Meyer 2015). Due to the fragility of the structure, the characterization biofilms is often performed in vitro. The thickness of the biofilms grown in vitro can vary between the bacterial species, for example, K. pneumoniae 231 μm, P. aeruginosa 209 μm, and S. aureus 8 μm (Singla, Harjai, and Chhibber 2014; Werner et al. 2004; Kamaruzzaman et al. 2017). Figure 17.2 shows the structure of S. aureus biofilms grown in vitro and visualized by confocal microscope with a thickness of approximately 8.0 μm.