Ozone Sensitivity and Catalase Activity in Pigmented and Non-Pigmented Strains of .

Background: Ozone exposure rapidly leads to bacterial death, making ozone an effective disinfectant in food industry and health care arena. However, microbial defenses may moderate this effect and play a role in the effective use of oxidizing agents for disinfection. is an opportunistic pathogen, expressing genes differentially during infection of a human host. A better understanding of regulatory systems that control expression of 's virulence genes and defenses is therefore valuable.

Objective: Here, we investigated the role of pigmentation and catalase in on survival to ozone exposure.

Method: Pigmented and non-pigmented strains of were cultured to exponential or stationary phase and exposed to 5 ppm of gaseous ozone for 2.5 - 10 minutes. Survival was calculated via plate counts. Catalase activity was measured photometrically and tolerance to hydrogen peroxide was assayed by disk-diffusion.

Results: Exposure of to 5 ppm gaseous ozone kills > 90% of cells within 10 minutes in a time and concentration-dependent manner. Although pigmented (grown at 28°C) survived ozonation better than unpigmented (grown at 35°C), non-pigmented mutant strains of had similar ozone survival rates, catalase activity and HO tolerance as wild type strains. Rather, ozone survival and catalase activity were elevated in 6 hour cultures compared to 48 hour cultures.

Conclusion: Our studies did not bear out a role for prodigiosin in ozone survival. Rather, induction of oxidative stress responses during exponential growth increased both catalase activity and ozone survival in both pigmented and unpigmented .