FIG 4.

Catalase alleviates growth inhibition of L. monocytogenes by blue light. (A) Wild-type overnight cultures were standardized, diluted serially, and spotted on BHI agar spread with catalase or on agar plates without catalase. The plates were incubated in the presence of light for 24 h. (B) Wild-type overnight cultures were diluted to an OD₆₀₀ of 0.05 and serially diluted 10-fold to a 10⁻⁶ dilution. The dilutions were grown for 24 h in the presence or absence of light, with or without catalase at a concentration of 125 U ml⁻¹. The 24-h endpoint and the time taken to reach an OD₆₀₀ of 0.1 were calculated for each strain condition at each dilution. The error bars represent standard deviations between samples. Unpaired t tests were used to determine the significance of differences (P ≤ 0.05, indicated by asterisks) between endpoint and lag-phase values between cultures with and without catalase.