Nucleic acid fluorochromes and flow cytometry prove useful in assessing the effect of chlorination on drinking water bacteria

Flow cytometry (FCM), combined with staining using two fluorochromes (propidium iodide, PI, or SYBR Green 11 RNA gel stain, SYBR-II), was used to assess nucleic acid injuries to chlorinated drinking water bacteria. Highly fluorescent SYBR-II-stained bacteria were converted to bacteria with low fluorescence after chlorination. PI staining of bacteria exposed to different doses of chlorine showed membrane permeabilisation ([Cl-2] < 0.2 mg L-1) and nucleic acid damage at higher doses ([Cl-2]> 0.3 mgL(-1)). Above a threshold dose (between 1.5 and 3mg Cl2L-1), nucleic acids appeared severely damaged and incapable of being stained by PI or SYBR-II. These results constitute evidence that FCM is a promising too] for assessing drinking water bacteria injuries and for controlling chlorine disinfection efficiency much more rapidly than the standard sensitive but time-consuming heterotrophic plate count method. (c) 2005 Elsevier Ltd. All rights reserved.