Analysis of the adaptation capacity of Staphylococcus aureus to commonly used antiseptics by microplate laser nephelometry.

BACKGROUND Bacterial colonization and infection are important factors in compromised wound healing. Antiseptics have become an alternative for antimicrobial applications as antibiotic resistance is increasing; they have multiple targets with a broad spectrum of activity. Hence, the risk for developing resistance should be low. However, concerns have been raised that their growing use may result in bacteria that are less susceptible. METHODS The capacity of common antiseptics such as silver nitrate, polihexanide, octenidine, chlorhexidine and polyvinylpyrrolidone (PVP)-iodine to induce adaptation in a Staphylococcus aureus strain was analyzed in vitro using microplate laser nephelometry. S. aureus was repeatedly incubated with the respective half maximal inhibitory concentration (IC(50)) over a time period of 100 days. The influence of the continued treatment was determined by in situ monitoring of changes in the dose-response curves and calculation of the current IC(50) values for the substances tested. RESULTS During the experiment, S. aureus quickly adapted to high concentrations of the antibiotic mupirocin during repeated treatment. Moreover, a significant increase of the IC(50) for silver nitrate was observed over time. On the other hand, no significant difference was observed for polihexanide or chlorhexidine. While the IC(50) for octenidine was also found to increase significantly, although the change was only marginal, reiterated incubation with PVP-iodine led to a decrease in the IC(50). CONCLUSION Repeated treatment of S. aureus with polihexanide, chlorhexidine, octenidine and PVP-iodine did not trigger bacterial adaptation to these substances.