Biofilm resistance

The preceding sections have focused on the molecular aspects of evolution of enzyme efficiency, specificity, and regulation. Flowever, it is important to remember that enzymes evolve in a cellular context. Natural selection acts upon the fitness of the organism, which is a complicated function of properties such as growth rate, robustness to environmental perturbations, ability to construct a protective biofilm, resistance to toxins, or synthesis of secondary metabolites that impair competitors. The catalytic capabilities of enzymes, as well as the repertoire of enzymes maintained by individual species of microbes, have been shaped by these environmental factors over billions of years. 

Davies, D. (2003). Understanding biofilm resistance to antibacterial agents. Nat. Rev. Drug Discov. 2,114-122. 

Elkins, J. G., Hassett, D. J., Stewart, P. S., Schweizer, H. P., and McDermott, T. R. (1999). Pseudomonas aeruginosa biofilm resistance to hydrogen peroxide Protective role of catalase. Appl. Environ. Microbiol. 65, 4594-4600. 

Rosman BM, Barbosa JA, Passerotti CP, Cendron M, Nguyen HT. Evaluation of a novel gel-based ureteral stent with biofilm-resistant characteristics. Int Urol Nephrol. 46(6) (2014) 1053-1058. 

Exopolysaccharides play a cracial role in the formation of biofilms and biofilm resistance to antimicrobials and innate host defense. Here we describe methods to analyze and quantify polysaccharide intercellular adhesin (PIA), a biofilm exopolysaccharide made of Af-acetylglucosamine that is found in staphylococci and many other bacterial biofdm-... 

Mah T-FC, O Toole GA. Mechanisms of biofilm resistance to antimicrobial agents. 

In practical sitiratiorrs, electrochemictJ systems are often more complex than the simple model assumed by the polarization resistance method. The presence of biofilms on the metal sirrface may introduce a capsrcitance as well as resisttmce to the interface. Moreover, the biofilm may introduce additional electrochemical reactions and adsorptive processes, which can lead to nonlinear polarization behavior. Even so, a polarization resistance value can be found as long as a sirfficiendy slow polarization scan rate (determined by the rate of the slowest reaction present) is used to maintain steady state conditions and a correction can be made for solution smd biofilm resistances. 

Conformal mapping (the Schwarz-Christoffel transformation) was employed to calculate conductivity from experimentally measured biofilm resistance. The details of the conformal mapping procedure are presented elsewhere [53, 58], Variables are defined in Figure 7.3a. In the limiting cases a [Pg.231]

It is important to note that antimicrobial and biofilm resistance are two different characteristics though some materials show both properties at the same time. Antimicrobial materials do not automatically prevent biofilm formation and vice versa. Antimicrobial surfaces could kill bacteria on contact but if dead bacteria cell debris blocks the active biocidal surface, biofilm formation could eventually occur. For example, quaternary anunonium polymers can effectively kill bacteria but when the surface is fouled with dead bacteria debris, biofilm formation is inevitable [188]. Materials with antibiofilm properties will repel the bacterial adhesion very effectively but may not kill the bacteria when they do colonize the surface. PEG surfaces are well known to repel bacteria adhesion. However, PEG surfaces show little antimicrobial activity. Quantitative antibiofilm efficacy tests can be divided into two categories static (minimum biofilm eradication concentration assay, MBEC) and dynamic (flow cell assay). In addition, SEM is a semiquantitative assay, which is discussed in Section 2.5. 

Many different mechanisms of biofilm resistance are discussed in the literature, reflecting the different ways of biofilm organisms to withstand biocides. These mechanisms include physical and chemical diffusion-reaction barriers in the biofilm restricting biocide penetration of the biofilm, slow growth rate of biofilm cells due to nutrient limitation, activation of general stress response genes, the emergence of a biofilm-specific phenotype, and the presence of persister cells. 

Other possible phenotypic changes that are discussed include decrease of membrane permeability due to alterations in membrane compositions or the upregulation of multidrug efflux pumps that could extrude biocide molecules from the cell interior (Gilbert et al., 2001 Mah and O Toole, 2001). However, additional studies are still necessary to elucidate the relevance of these mechanisms for biofilm resistance to biocides. 

Ntsama-Essomba et al. (1997) reported a minimal bactericidal concentration (decrease of colony counts by 5 log units) of 195 mg/L available chlorine when 5-day-old E. coli biofilms on PVC surfaces were treated for 5 min with a sodium hypochlorite-containing product the minimal bactericidal concentration towards planktonic cells was five times lower. The age of biofilms influenced chlorine activity the minimal bactericidal concentration towards 10-day-old biofilms was 10 times higher than for 5-day-old biofilms (Ntsama-Essomba et al., 1997). A similar observation was reported by LeChevallier et al. (1988a). Reduction of viable counts of 2-day-old K. pneumoniae biofilms was more than two log units higher than for 7-day-old biofilms, when the biofilms were exposed for 10 min with 1 mg/L of free chlorine (pH 7.0). No age-related increase in biofilm resistance was observed when the biofilms were treated with 5 mg/L of monochloramine under the same conditions (LeChevallier et al., 1988a). 

Anderl, J. N., Franklin, M. J. and Stewart, P. S., 2000. Role of antibiotic penetration limitation in Klebsiella pneumoniae biofilm resistance to ampicillin and ciprofloxacin. Antimicrobial Agents and Chemotherapy 44, 1818-1824. 

Lewis K (2000) Programmed death in bacteria. Microbiol Mol Biol Rev 64 503-514 Lewis K (2001) Riddle of biofilm resistance. Antimicrob Agents Chemother 45 999-1007 Lewis K (2007) Persister cells, dormancy and infectious disease. Nat Rev Microbiol 5 48-56 Lewis K, Ausubel FM (2006) Prospects for plant-derived antibacterials. Nat Biotechnol 24 1504-1507... 

Cheddar cheese Lact. curvatus biofilm-formers Biofilms resist to vat surface sensory quality D conversion of LX+)- to D(-) lactic acid (Somers et al. 2001 ... 

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