Effect of Antibiotic-Induced Sigma B Activity on the Pathogenicity in Drug-Resistant Staphylococcus aureus

The alternative transcription factor σB is responsible for the stress response in the major pathogenic bacterium Staphylococcus aureus. Many virulence-associated genes are directly or indirectly regulated by σB. We hypothesize that treatment with antibiotics may act as environmental stresses to induce σB activity in antibiotic-resistant strains. Several antibiotics with distinct modes of action were investigated for their ability to activate this transcription factor, even in vancomycin-resistant S. aureus (VRSA) strains. Recent findings in this laboratory indicate that cell wall-active antibiotics, such as vancomycin and ampicillin, can induce σB activity in three of four of our tested strains. Downstream virulence-associated genes, including agrA, hla and fnbA, were affected by the antibiotic-induced σB regulatory pathways in those strains. Cytotoxicity was increased by antibiotic treatment in the same strains. We should take into consideration that the improper use of antibiotics has the potential risk to induce the expression of virulence factors in drug-resistant S. aureus and lead to clinically worse outcomes. We would like to investigate whether the in vitro worse outcome will be happened in vivo and the role of σB in mediating antibiotic stress signal. A mouse systemic infection model will be employed to evaluate the bacterial pathogenicity upon inadvertent antibiotic treatment. sigB gene in VRSA strains will be deleted by insertional mutation. Two strains of mice, BALB/c and C57BL/6 will be inoculated with wild-type or sigB-deleted VRSA strains by tail intravenous injection in the presence or absence of vancomycin administration. For the pathogenicity determination, mice survival rate, physiological status, bacterial load, and histopathological examination will be evaluated. Inflammatory cytokines/chemokines, such as IL-1β, IL-6, TNF-α, interferon-γ, KC, and MIP-2 will also be determined. In addition, the ability of S. aureus to form biofilm on indwelling medical devices makes this pathogen more resistant to antibiotic treatments and enhances the genetic exchange of drug-resistant determinants among this single- or multi-species grown within a biofilm. σB is also involved in the biofilm formation. The impact of antibiotic-induced σB activity on biofilm development will be studied.

Project ID:PC9907-2519
External Project ID:NSC99-2320-B182-009-MY3