Effects of starvation on physiological activity and chlorine disinfection resistance in Escherichia coli O157 : H7

Escherichia coli O157:H7 can persist for days to weeks in microcosms simula ting natural conditions. In this study, vee used a suite of fluorescent, in situ stains and probes to assess the influence of starvation on physiologi cal activity based on membrane potential (rhodamine 123 assay), membrane in tegrity (LIVE/DEAD BacLight lilt), respiratory activity (5-cyana-23-di-4-to lyl-tetrazolium chloride assay), intracellular esterase activity (ScanRDI a ssay), and 16S rRNA content, Growth-dependent assays were also used to asse ss substrate responsiveness (direct viable count [DVC] assay), Am activity (MicroStar assay), and culturability (R2A agar assay), In addition, resista nce to chlorine disinfection was assessed, After 14 days of starvation, the DVC values decreased, while the values in all other assays remained relati vely constant and equivalent to each other. Chlorine resistance progressive ly increased tl;rough the starvation period After 29 days of starvation, th ere was no significant difference in chlorine resistance between control cu ltures that had not been exposed to the disinfectant and cultures that had been exposed, This study demonstrates that E. cati O157:H7 adapts to starva tion conditions by developing a chlorine resistance phenotype.