[Evaluation of resistance mechanism against antimicrobial factors in gram positive bacteria]

It is known that various antibacterial agents are observed in human for preventing bacterial infection. In this study, in order to elucidate the resistance mechanism against antimicrobial agents derived of human and bacteriocins derived of commensal bacteria, we systematically evaluated the roles of the bacteria-specific two-component systems of Staphylococcus aureus and Streptococcus mutans which colonize to different sites. Two-component systems (TCSs) are specific regulatory systems in bacteria that play an important role in sensing and adapting to the environment. As the result, four TCSs of S. aureus and three TCSs of S. mutans were associated with resistance against defensin and LL37 as antimaicrobial peptides and nisin A and nukacin ISK-1 as bacteriocins. Two TCSs that are individually associated with resistance against the bacteriocins nisin A (class I type A[I]) and nukacin ISK-1 (class I type A[II]) were identified in S. mutans, whereas one TCS is associated with main resistance against the both of nisin A and nukacin ISK-1. This result suggested that TCSs play important roles on acquisition of human- and bacteria-derived antibacterial agents. However, the resistance mechanism via TCS in S. aureus is quite different from that of in S. mutans. Additional evidence suggests that these TCSs are required for co-existence with other bacteria producing to nisin A or nukacin ISK-1, meaning that the roles of bacteriocins in the interactions between different species of commensal bacteria and the importance of TCSs in this process. Our results will highlight the roles of bacterial colonization in human being are constituted on the adaptation against antibacterial agents derived from human and commensal bacteria via TCSs.