Emerging Strategies for the Chemical Treatment of Microbial Biofilms

Abstract

Over the past decade, several strategies have been proposed for the control of surfaceassociated tnicrobial populations. Physical methods, including electrification, ultrasonication, application of ablative laser light and mechanical cleaning or scraping are generally effective at removing sutface growth. Chemical control methods, on the other hand, are often ineffective. This has led to a notorious association of biofilms with resistance towards antibiotics, biocides and disinfectants. In such respects, reaction-diffusion limitation of the passage of oxidizing biocides and antibiotics, across biofilms aided by the presence ofextracellular enzymes often causes the failure of such agents to sanitize contaminated surfaces. Deep-lying cells within biofilms are often also severely nutrientand oxygen..litnited, causing the expression of starvation phenotypes, which include multi-drug efflux pumps and enhanced exopolylner synthesis. During exposure to antimicrobial agents, these slow growing organislns1 being exposed to sub-lethal levels of agent, will generaHy out-survive their less nutrient-depleted congeners. This Inay well enrich the population for drug resistant phenotypes and genotypes during the post...treatment phase. Emerging biofihn treatment methodologies are based 011 our knowledge of biofilm physiology and resistance mechanisms. For example, in an attempt to prevent early colonization of surfaces and in order to overcome reaction..diffusion limitation, treatnlent agents may be coated onto or incorporated into the substrate to be protected. More sophisticated approaches have been developed, with varying success, that deploy erodable~ biocide-containing coatings. Erosion, in this instance being intended to purge the surface of attached bacteria and cellular debris. At the vanguard of emerging control strategies are surface-catalyzed hygiene and anti cell-cell signalling chemicals.