Role of RpoS and AlgT in Pseudomonas aeruginosa biofilm resistance to hydrogen peroxide and monochloramine

The role of two sigma factors, AlgT and RpoS, in mediating Pseudomonas aeru ginosa biofilm resistance to hydrogen peroxide and monochloramine was inves tigated. Two knock out mutant strains, SS24 (rpoS(-)) and PAO6852 (algT(-)) , were compared with a wild type, PAO1, in their susceptibility to monochlo ramine and hydrogen peroxide. When grown as biofilms on alginate gel beads (mean untreated areal cell density 3.7 +/- 0.27 log cfu cm(-2)) or on glass slides (mean untreated areal cell density 7.6 +/- 0.9 log cfu cm(-2)), wil d type bacteria exhibited reduced susceptibility to both antimicrobial agen ts in comparison with suspended cells. On alginate gel beads, all strains w ere equally resistant to monochloramine. rpoS(-) and algT(-) gel bead biofi lms of 24-hour-old were more susceptible to hydrogen peroxide disinfection than were biofilms formed by PAO1. Biofilm disinfection rate coefficients f or the two mutant strains were statistically indistinguishable from plankto nic disinfection rate coefficients, indicating complete loss of biofilm res istance. While 48-hour-old algT(-) biofilm cells became resistant to hydrog en peroxide, 48-hour-old rpoS(-) biofilm cells remained highly susceptible. With the thicker biofilms formed on glass coupons, all strains were equall y resistant to both hydrogen peroxide and monochloramine. It is concluded t hat while RpoS and AlgT may play a transient role in protecting thin biofil ms from hydrogen peroxide, these sigma factors do not mediate resistance to monochloramine and do not contribute significantly to the hydrogen peroxid e resistance of thick biofilms.