Impact of Hydrogen Peroxide Treatment on Environmental Escherichia coli Strains

Abstract

The impact of three hydrogen peroxide (H2O2) concentrations (250, 300 and 350 mg.L-1) at 30, 60, 90 and 120 min time intervals was determined on environmental and ATCC reference E. coli strains (n=11). Variation between strains was evident and treatment resulted in significantly different log reductions after the 120 min contact time. The environmental strains were generally more resistant than the reference strains. A H2O2 resistant environmental strain (M53) and a potential pathogenic strain (W1371) were used to determine bactericidal effect at higher (and a lower) H2O2 concentrations of 50, 350, 700 and 1 000 mg.L-1 on the microbial inactivation. Bacterial inactivation increased as concentration increased, with 50 mg.L-1 resulting in low microbial inactivation and 1 000 mg.L-1 resulting in an effective (>4 log) reduction. A significant difference in microbial reduction was not observed at H2O2 concentrations between 350 and 700 mg.L-1. The potential influence of the COD (chemical oxygen demand) of river water on the H2O2 treatment was also determined. It was observed that the water COD, at the levels investigated, might influence H2O2 efficacy treatment over shorter treatment times (30 min), but not over longer periods (90-120 min). Different levels of catalase activity were also measured for the test strains. A trend was observed between H2O2 resistance and an increased amount of HPII catalase activity. However, it was also observed that E. coli can also employ other protection mechanisms, as two of the most resistant environmental E. coli strains only indicated average catalase activity.