Fig 1.

Depression of virulence factor mRNA levels in S. aureus treated with fatty acid synthesis inhibitors. Strain RN4220 was grown to mid-log phase in tryptone broth and treated with either AFN-1252 (50 ng/ml), cerulenin (500 μg/ml), or clarithromycin (1.5 μg/ml) for 15 min to arrest either lipid or protein synthesis. The MICs for these drugs in strain RN4220 determined in tryptone broth as described previously (7) were as follows: AFN-1252, 4 ng/ml; cerulenin, 62 μg/ml; and clarithromycin, 310 ng/ml. RNA was extracted, and the levels of four randomly selected virulence factor mRNAs (saeP, ehp, efb, and hlgC) were calculated and averaged, in addition to fabH, by quantitative RT-PCR. Significance between treated and untreated samples was calculated using the Student t test, and standard deviations were obtained from triplicate determinations derived from triplicate experiments. fabH mRNA was significantly increased in response to AFN-1252 and cerulenin (*, P < 0.05) but not significantly altered by clarithromycin. The average levels of virulence gene mRNAs were significantly decreased in response to AFN-1252 and cerulenin (*, P < 0.05). Clarithromycin-treated cells had a modest increase in virulence gene expression, but it was not significant.