Protective role of catalase in Pseudomonas aeruginosa biofilm resistance to hydrogen peroxide

Microbial biofilm formation on man-made surfaces can profoundly impact human health and welfare. Biofilms readily develop on medical implants such as catheters and artificial joints causing chronic infections. Industrial processing systems are also plagued with the accumulation of biofilm in pipes, heat exchangers, cooling towers, and other equipment resulting in the loss of system efficiency. Biofilm bacteria are tremendously more difficult to kill with antimicrobial agents than freely suspended organisms. The basis for biofilm resistance to antimicrobial agents has been investigated but, the primary mechanisms responsible for this phenomena are still poorly understood. It has been hypothesized that biofilm bacteria are able to rapidly adapt to an antimicrobial agent and neutralize it with protective proteins/enzymes. This hypothesis was addressed in this study by investigating the adaptive response of Pseudomonas aeruginosa biofilms to the oxidizing biocide, hydrogen peroxide (H2O2). P. aeruginosa expresses two catalase enzymes in defense against H2O2 known as KatA and KatB. These enzymes catalyticaly degrade H2O2 into oxygen and water. P. aeruginosa mutants that are unable to synthesize either KatA or KatB were tested for their susceptibility to H2O2 when grown as planktonic cells and biofilms. Biofilms lacking KatA activity were more susceptible to H2O2 than the wild-type or KatB- strain but remained much more resistant to the biocide than planktonic cultures