Effects of a topical essential oil-containing formulation on biofilm-forming coagulase-negative staphylococci

Aims: To evaluate the antimicrobial effects of Polytoxinol(TM) (PT), a topical essential oil-based formulation, against biofilm positive strains of coagulase-negative staphylococci. Methods and Results: Using a microtitre plate assay we measured inhibitory effects for PT against a selection of biofilm-forming clinical isolates of coagulase-negative staphylococci. Susceptibility varied considerably (MIC = 0.6-20 000 ppm). For the most tolerant clinical isolate (Staphylococcus warneri) biofilm growth was inhibited by a 32-fold lower PT concentration than planktonic growth. This inhibition of biofilm development, which was not observed with the other test isolates, was related to an inhibition of the initial phase of S. warneri cell adherence to the polystyrene surface. Conclusion: The antimicrobial efficacy of PT was verified against clinical isolates of coagulase-negative staphylococci in vitro. PT was able to inhibit biofilm formation in the most tolerant isolate at sub-inhibitory concentrations. Significance and Impact of the Study: These observations indicate that an ability to prevent biofilm formation, independently of effects on cell viability may contribute to the in vivo topical efficacy of essential oils.