Ozone Sensitivity and Catalase Activity in Pigmented and Non-Pigmented Strains of Serratia Marcescens

Abstract

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.Serratia marcescensis an opportunistic pathogen, expressing genes differentially during infection of a human host. A better understanding of regulatory systems that control expression ofSerratia’s virulence genes and defenses is therefore valuable.Objective:Here, we investigated the role of pigmentation and catalase inSerratia marcescenson survival to ozone exposure.Method:Pigmented and non-pigmented strains ofSerratia marcescenswere 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 ofS. marcescensto 5 ppm gaseous ozone kills > 90% of cells within 10 minutes in a time and concentration-dependent manner. Although pigmentedSerratia(grown at 28°C) survived ozonation better than unpigmentedSerratia(grown at 35°C), non-pigmented mutant strains ofSerratiahad similar ozone survival rates, catalase activity and H2O2tolerance 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 unpigmentedS. marcescens.