Antimicrobial tolerance changes in biocide-passaged biofilm cultures of Pseudomonas aeruginosa PAO1

Abstract

The aim of this study was to develop a novel process for the passaging of biofilms of Pseudomonas aeruginosa towards tolerance to a group of selected antimicrobial agents (biocides). The combination of both a traditional passage approach coupled with a suitable biofilm model, for the production of large numbers of adherent cells, yielded evidence of a development of phenotypic tolerance in Ps. aeruginosa towards selected biocides (zinc pyrithione (ZnPT), sodium pyrithione (NaPT), Cetrimide & Benzisothiazolone (BIT)). The results indicate a step-wise increase in minimal inhibitory concentration (MIC) over a series of ten consecutive passages in the presence of increasing concentrations of biocide. Scanning electron microscopy revealed a complex internal structure to the biofilms grown using this model. Results indicate that it is possible to passage cultures of Ps. aeruginosa towards phenotypic tolerance to selected antimicrobial agents. Results also indicate that such tolerance is partially reversible and that some residual tolerance remains in the absence of biocide. Thus, indicating that the tolerance is partially due to phenotypic changes within biofilm cells. This study describes a novel technique for the induction of phenotypic tolerance towards antimicrobial agents in biofilm situations. The model used here may be adapted to other areas of biofilm work, where clonal selection of phenotypic traits may be desirable.