1996 Volume 19 Issue 5 Pages 381-387
Many researchers have studied the injury of enteropathogenic bacteria in water induced by chlorine, but there have been little research on the injury induced by chloramine. The purpose of this study is to compare the injuries of enterotoxigenic Escherichia coli induced by chloramine and by free chlorine. The injury was assessed by determining the difference between the number of CFU on nonselective TSA and the number of CFU on selective TSA supplemented with 0.02% sodium deoxycholate. The results can be summarized as follows: 1) Chlorine injury increased with contact time and almost all of surviving cells were injured finally, while chloramine injury increased with contact time and a considerable number of surviving cells were not injured. 2) Chlorine injury can be described by two-hit model assuming that injury is caused by one-hit, while chloramine injury appears to be described by a modified two-hit model considering inactivation of injured cells independent of chloramine concentration. 3) The presented models showed that chlorine injury is always larger than chloramine injury when compared at the same survival ratio, and that a combination of low chloramine concentration and long contact time is more effective than a combination of high chloramine concentration and short contact time.
