Figure 3

Growth and survival of L . monocytogenes strains in sublethal and lethal concentrations of penicillin G. (A) Growth of wild-type L. monocytogenes EGD (black circle), the ΔaxyR mutant (black diamond), ΔphoP mutant (black square) and Δfri mutant (black triangle) in sublethal concentration of penicillin G. BHI broth supplemented with penicillin G (0.09 μg/ml) was inoculated with an overnight culture of each strain (1:100) and incubated with shaking at 37°C. Cell growth was measured spectrophotometrically by determining the OD₆₀₀. (B) Survival of wild-type L. monocytogenes EGD (black circle), the ΔaxyR mutant (black diamond), ΔphoP mutant (black square) and Δfri mutant (black triangle) in a lethal concentration of penicillin G. BHI broth supplemented with 32 μg/ml penicillin G was inoculated with a mid-exponential culture of each strain (5 × 10⁷ CFU/ml) and incubated with shaking at 37°C. Viable cell counts were performed by plating serial dilutions of culture samples onto BHI agar and counting colonies after 24–48 h incubation at 37°C. The mean values from three independent experiments are plotted and the error bars represent the standard deviation.