Resistance of Bacillus subtilis biofilms to hydrogen peroxide and UV-C radiation

Abstract

Biofilms are microbial communities that have sophisticated protective mechanisms which renders them highly resistant to i.e., common disinfectants. They can lead to some microbiological induced problems like e.g., a socio-economic burden by causing serious health problems and high costs to industry. Endospore-formation and horizontal gene transfer (HGT) are two major features that contribute to bacterial resistance. Endospores are considered the most resistant cell forms, and HGT allows the exchange of protective genes between individual cells within the population. In this study, the protective effect of these properties within a biofilm is investigated. For this purpose, different growth states of biofilms of the endospore former B. subtilis were treated with 3% hydrogen peroxide and UV-C radiation at 254 nm, both of which commonly used sterilising agents. Biofilms of strains NCIB3610, DK1042 and NCIB3610ΔsigG were used for the experiments. NCIB3610 is a wild-type strain, DK1042 is competent for DNA uptake and can hence perform a form of HGT, and NCIB3610ΔsigG is an endospore-deficient strain. The results of this study show that neither sporulation ability nor competence contribute to the resistance, suggesting that additional factors may be used by B. subtilis biofilms to withstand the stress induced by the stress conditions tested. In future research, it is important to further investigate the different mechanisms of horizontal gene transfer and the effect of extracellular polymeric substances (eps). A multicomponent sterilisation approach such as gas plasma discharge would be highly interesting to study.