Figure 7

Nicotine treatment suppresses S. aureus virulence. (A) Transcriptional levels of the virulence genes in S. aureus USA300 strain cultured in TSB and TSB supplemented with 2 mg/mL nicotine for 12 h/24 h were detected by qRT-PCR(n = 3). In the nicotine-treatment group, the expression of the virulence genes, hla, hlb, pvl, nuc, ssp, spa, sigB was downregulated at both 12 h and 24 h, while expression of the coagulase gene coa and the pigmentation-related gene crtN was downregulated at 24 h. (B) The S. aureus USA300 strain was inoculated on normal blood agar plates (left) and blood agar plates containing 2 mg/mL nicotine (right), respectively. After incubation at 37 °C for 24 h, a smaller β-hemolytic ring (β-hemolytic phenotype) was formed on the blood agar plate containing nicotine than the control. (C) Nicotine treatment suppressed carotenoid pigment formation. The S. aureus USA300 strain was cultured for 24 h in TSB (left) and TSB supplemented 2 mg/mL with nicotine (right) respectively. The pigment formed by bacterial cell pellets in nicotine group was reduced as compared to the control. Pigment production was quantified at OD₄₆₂, decreasing from 0.263 ± 0.01 in the control group (n = 3) to 0.119 ± 0.01 in the nicotine-treated group (n = 3). These photos are representative of three independent experiment.