UCLA

Due to the growing concern about antibiotic-resistant bacteria (ARB) in water, there have been many studies on inactivation of ARB by chlorination. In order to examine possible increase in ARB concentrations after a retention time, this study was performed to explore not only inactivation, but also reactivation of Escherichia coli (E. coli) K12. Observed immediately after chlorination for 10 minutes, inactivation results demonstrated that even ampicillin concentration of 2 mg/L enhances inactivation of bacteria nearly up to 100%. Reactivation of surviving cells was observed after 24-h retention time in the study. Reactivation results showed that MIC50 and MIC90 for 0 mg Cl2/L were below 4 mg/L of ampicillin. However, both MIC50 and MIC90 were much higher after chlorination; MIC50 and MIC90 for 1 mg Cl2/L were greater than 16 mg/L of ampicillin. The study indicates that there is a risk of regrowth of ARB even after 1-day of standing period. Therefore, immediate attention on ARB treatment is required to protect public health.