Biofilms, homoserine lactones and biocide susceptibility

Aims: To investigate the susceptibility, to a range of different biocides, of Pseudomonas aeruginosa strains variously deficient in N-acyl homoserine lactone systems, grown either as planktonic or biofilm populations. Methods and results: Biocide susceptibility data were generated for strains of P. aeruginosa deficient in N-acyl homoserine lactone production, grown planktonically or as biofilm populations using a poloxamer hydrogel construct. Component cells from the biofilm constructs were also tested for their susceptibility. Significant differences in susceptibility were noted between the wild-type strain, a mutant defective in the long chain (C-12) homoserine lactone and a mutant defective in the short chain (C-4) homoserine lactone which could not be related to the biofilm mode of growth. Moreover, differences in susceptibility appeared to be dependent upon the nature of the homoserine lactone deletion and type of biocide rather than the mode of growth. Conclusions: No general trend exists between homoserine lactone deficiency and biocide susceptibility regardless of mode of growth.