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

José De Ondarza

doi:10.2174/1874285801711010012

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 marcescens is an opportunistic pathogen, expressing genes differentially during infection of a human host. A better understanding of regulatory systems that control expression of Serratia’s virulence genes and defenses is therefore valuable.Objective:Here, we investigated the role of pigmentation and catalase in Serratia marcescens on survival to ozone exposure.Method:Pigmented and non-pigmented strains of Serratia marcescens 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 S. marcescens to 5 ppm gaseous ozone kills > 90% of cells within 10 minutes in a time and concentration-dependent manner. Although pigmented Serratia (grown at 28°C) survived ozonation better than unpigmented Serratia (grown at 35°C), non-pigmented mutant strains of Serratia had similar ozone survival rates, catalase activity and H2O2 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 S. marcescens.

Highlights

Ozone is a potent oxidizing agent that occurs naturally in the atmosphere at low (< 50 ppb) concentrations, but can rise to levels as high as 200 – 300 ppb in smog
Whereas the purple pigment violacein can function as an anti-oxidant [22], such a role has yet to be demonstrated for prodigiosin, a red pigment produced by Serratia marcescens
Both mutant strains exhibited similar survival following 5 ppm ozone exposure as their pigmented counterparts (Fig. 2), strongly suggesting that pigmentation may not be responsible for the observed difference in sensitivity to ozone

Summary

Introduction

Ozone is a potent oxidizing agent that occurs naturally in the atmosphere at low (< 50 ppb) concentrations, but can rise to levels as high as 200 – 300 ppb in smog. A wide variety of pathogens respond differently to ozone disinfection, raising the question of whether sensitivity to ozone can be moderated by specific microbial defenses such as catalase, superoxide dismutase, or other antioxidant systems. Microbial responses such as elevation of SOD and catalase activity have been demonstrated in Listeria [8] and E. coli [9] in response to ozone exposure. Microbial pigmentation offers another potential defense against environmental challenges, including predation [14, 15], competition (antibiotic effects), and potentially, oxygen radicals [16 - 18] Such pigments are often produced by bacteria as secondary metabolites via a quorum-sensing mechanism, including prodigiosin and violacein [19 - 21]. A better understanding of regulatory systems that control expression of Serratia’s virulence genes and defenses is valuable

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Results

Discussion

Conclusion