FIG 2.

Penicillin tolerance of WT and Arc mutant GAS. Planktonic cultures of the WT strain and arc mutant were grown either to mid-log phase (approximately 4 to 5 h) (A) or for 24 h (B) and exposed to the indicated concentrations of penicillin (PEN) for 4 and 24 h. (C to H) Biofilm cultures of the WT strain and arc mutant (C and E to H) or the WT strain, arc mutant, WT-NC, and arc mutant rescue strain (D) were grown for 48 h and exposed to the indicated concentrations of penicillin for 4 and 24 h. (E and F) Biofilm cultures of the WT and arc mutant strains were grown for 48 h and exposed to the following concentrations of the indicated antibiotic for either 4 h (E) or 24 h (F): AMP (ampicillin, 5 μg/ml), CFP (cefoperazone, 150 μg/ml), RIF (rifampin, 7 μg/ml), ERY (erythromycin, 2 μg/ml), and CLI (clindamycin, 14 μg/ml). (G and H) Biofilm cultures of the WT and arc mutant strains were grown for 48 h on either THY-A_L-arg, THY-A_7.5, THY-A_6.5, or THY-A_6.5+L-arg and then exposed to 20 μg/ml penicillin G for either 4 h (G) or 24 h (H). Data presented represent the means ± SD from three independent experiments measuring either the log₁₀ fold reduction in CFU versus an untreated culture (log fold reduction_untreated or log fold reduction_biofilm). *, P < 0.05; **, P < 0.01; ***, P < 0.001.