The sensor kinase BfmS mediates virulence in Acinetobacter baumannii.

BACKGROUND/PURPOSE BfmR, the response regulator component of the two-component system BfmRS, has important roles in biofilm formation and cellular morphology of Acinetobacter baumannii. Until now, the contribution of the sensor kinase BfmS to the virulence of this bacterium remains unknown. In this study, a bfmS knockout and complementation studies were performed to clarify the role of BfmS in A. baumannii virulence. METHODS We constructed a bfmS knockout mutant in the A. baumannii 17978 type strain by transposon inactivation. To clarify the role of bfmS in A. baumannii virulence, the biofilm formation, adherence ability to eukaryotic cells, serum resistance, and antibiotic susceptibility tests were performed in A. baumannii 17978 and its derivative knockout and complementation strains. RESULTS The bfmS knockout displayed a reduction in biofilm formation, loss of adherence to eukaryotic cells, and greater sensitivity to serum killing compared with the parent strain. Proteomic analysis of culture supernatants revealed that the release of outer membrane proteins (Omps), including CarO and outer membrane protein A (OmpA), was associated with the inactivation of BfmS in A. baumannii. CONCLUSION This study is the first to demonstrate that the pathway regulated by the sensor kinase BfmS is associated with biofilm formation, adherence to biotic surfaces, serum resistance, and antibiotic susceptibility, which may be associated with the release of Omps in A. baumannii.