Fig 2.

Relative virulence factor production by S. aureus strains. (A) Basal level of virulence factor mRNA levels in a panel of S. aureus strains. The expression level in strain PDJ22 (ΔsaeR) was then set to 1, and the expression levels in the indicated strains were compared to the levels in the saeR-knockout strain. The differences between strains PDJ22 and USA300 were not significant. Strains Wood46, RN4220, and Newman exhibited significantly higher levels of virulence factor mRNA than did strains PDJ22 and USA300. *, P < 0.05. (B) Levels of virulence factor and fabH mRNA in strains treated with AFN-1252. In both experiments, the mRNA levels of four virulence-related genes (ehp, efb, hlgC, and saeP) and fabH were measured by qRT-PCR using gmk as the internal control, and triplicate determinations for each gene were averaged. Expression of fabH was significantly increased in all cases (*, P < 0.05). Virulence gene expression was only significantly decreased by 8- to 10-fold in strains Wood46 and RN4220 (*, P < 0.05). All strains had the same MIC for AFN-1252, 4 ng/ml (7). Significance between treated and untreated samples was calculated using the Student t test, and error bars indicate standard deviations.