The use of multiple indices of physiological activity to access viability in chlorine disinfected Escherichia coli O157 : H7

A suite of fluorescent intracellular stains and probes was used, in conjunc tion with viable plate counts, to assess the effect of chlorine disinfectio n on membrane potential (rhodamine 123; Rh123 and bis-(1,3-dibutylbarbituri c acid) trimethine oxonol; DiBAC(4)(3)), membrane integrity (LIVE/DEAD BacL ight kit), respiratory activity (5-cyano-2,3-ditolyl tetrazolium chloride; CTC) and substrate responsiveness (direct viable counts; DVC) in the commen sal pathogen Escherichia roll O157:H7. After a 5 min exposure to the disinf ectant, physiological indices were affected in the following order: viable plate counts > substrate responsiveness > membrane potential > respiratory activity > membrane integrity. In situ assessment of physiological activity by examining multiple targets, as demonstrated in this study, permits a mo re comprehensive determination of the site and extent of injury in bacteria l cells following sublethal disinfection with chlorine. This approach to as sessing altered bacterial physiology has application in various fields wher e detection of stressed bacteria is of interest.