FIG 7.

Expression of α-psm is decreased in S. aureus isolates resistant to C. pseudodiphtheriticum-mediated bactericidal activity. Expression of α-psm and pmt was measured by qRT-PCR using primers specific to psmα₁ or pmtA, the first gene in each operon, respectively. (a and b) RNA was isolated from S. aureus LAC, Mu50, and 2014.N (a) and two spontaneously resistant 2014.N mutant strains (Survivors A and B) (b) after 24 h of incubation at 28°C on BHIT agar. α-psm and pmt gene expression is shown relative to 16S rRNA gene expression for three independent biological replicates. The data were plotted as follows: the geometric mean is represented as a bar, and error bars represent ±1 geometric standard deviation. A two-way ANOVA with Dunnett’s corrections for multiple comparisons was performed. The symbols above the graph indicate the following: *, P < 0.05; **, P < 0.01; and ***, P ≤ 0.001, for differences in α-psm and pmt gene expression for 2014.N versus the indicated strains. (c) 2014.N and 2014.N Survivor A strains were cultured overnight in BHIT broth. The total quantities of PSMs present were analyzed and measured by reverse-phase liquid chromatography–mass spectrometry. Bars represent arithmetic means from three independent biological replicates ±1 standard deviation. A two-tailed Student t test with Welch’s correction was performed on total PSM quantity. The symbol * above the graph indicated a statistically significant difference between 2014.N and Survivor A (P = 0.048).