Abstract/Summary

Resistance to the bactericidal effects of bile is crucial for the survival of Staphylococcus aureus in the human gut. This study was conducted to identify and characterize components of the bacteria, which allow it to resist bile acids. A comparative study was used to investigate the natural protein diversity within the Staphylococcus in relation to bile resistance. Imaging of one-dimension gel electrophoresis showed a unique protein band in samples prepared from bile-treated S. aureus. Mass spectrometry and database analysis showed the protein to be FadB. which has a role in lipid metabolism in Escherichia coli. It is hypothesized that fadB was responsible for the observed bile salt resistance phenotype; to test this, a ΔfadB strain was created in S. aureus SH1000. The mutant phenotype showed a significant decrease in viability upon exposure to bile acids in comparison with the parental wild type. Furthermore, survival of S. aureus ΔfadB was attenuated in an in vitro human colonic model, implicating fadB in S. aureus colonization of the human intestine. Moreover, upregulated expression of fadB was detected upon exposure to bile salts. To further confirm the role of FadB in bile salt resistance, the gene was cloned under the control of an inducible promoter, which enabled arabinose-dose dependent expression of fadB in E. coli JW113 as a heterologous host, confirming a bile resistant phenotype. Recombinant FadB was purified and shown to have affinity for cholic acid and might possess an ability to modify bile salts.