<i>Bacillus cereus</i>Group Exhibits More Resistant to Chlorhexidine Rather Than <i>Bacillus subtilis</i>Group

Chlorhexidine is a widely used antiseptic agent;however, its bactericidal effect against bacterial endospores is limited. The genus Bacillus is spore-forming gram-positive bacteria that are ubiquitously found in the environment and cause opportunistic infection and food poisoning. The susceptibility of bacterial endospores to chlorhexidine was previously evaluated in Bacillus subtilis, but the primary target for disinfection with antiseptic agents, including chlorhexidine, should be harmful strains. We aimed to evaluate the susceptibility of harmful cereus group including Bacillus cereus, and to compare that with harmless Bacillus species, containing B. subtilis. We evaluated the susceptibility of the 15 strains of the cereus group to chlorhexidine in comparison with the 5 other strains, named the subtilis group in this study. Our results indicated that chlorhexidine exerted a bacteriostatic effect against Bacillus species at practical concentrations, especially during long-term exposure. The strains of B. cereus group in this study displayed relatively lower susceptibility to the antiseptic than the B. subtilis group according to the minimum inhibitory and bactericidal concentrations. We concluded that there are intrinsic differences in the susceptibility to chlorhexidine between the groups, but the molecular mechanisms are unknown. The minimum inhibitory or bactericidal concentrations of disinfectants other than chlorhexidine may also need to be clarified in the B. cereus and B. subtilis groups.