FIG 1 .

agr deficiency increases bacterial survival following exposure to antimicrobial and environmental stresses. Wild-type S. aureus Newman (BS12) and the Δagr strain (BS13) were grown to late log phase in TSB and treated with the indicated concentrations of gentamicin for 60 min (A) or with 60 μg/ml of gentamicin for the times indicated (C). Likewise, cultures were treated with indicated concentrations of ciprofloxacin for 60 min (B) or with 10 μg/ml of ciprofloxacin for the times indicated (D). At the end of treatment, aliquots were removed, serially diluted, and plated for determination of viable counts, from which percent survival was calculated relative to a sample taken at the time of drug addition. Similarly, cells grown to late log phase in TSB were incubated at the indicated temperatures for 10 min (E) or in acidic TSB (pH 3.0) for indicated times (F). Symbols: filled circles, Δagr strain; empty circles, wild type. Data represent means from biological replicates ± standard deviations (n = 3).