Selection of chlorine tolerant E. coli O157:H7

Victoria Norma Ochoa, University of Texas at El Paso


Enterohemorragic E. coli O157:H7 strains have been recognized as a cause of serious gastro-intestinal infections in humans, acquired by ingestion of contaminated food and water. E. coli O157 has been recovered from municipal water supplies, suggesting some chlorine tolerance mechanism. Chlorine-resistant clones of the genomic strain Sakai of E. coli O157:H7 were selected during six passages of chlorine exposure. Clones with stable resistance levels greater than 5 times than the wild-type were obtained. Results of a panel of twenty-eight biochemical tests were unchanged in the resistant clones. The resistance mechanism appears to be a reduction of cell wall permeability, as shown by a lowering of fluorescence of nucleic acid stain SYTO-16 and propidium iodide with the majority of selected clones. Data suggesting also that the increased chlorine tolerance appears to be multifactorial, including increases in catalase activity and potentially other changes to counteract the oxidative damage generated by chlorine. Chlorine applies selective pressure on the vast number of prokaryotic organisms in our municipal water systems, the effects of which are still unclear. ^

Subject Area

Biology, Microbiology|Engineering, Civil|Engineering, Sanitary and Municipal|Health Sciences, Public Health|Engineering, Environmental

Recommended Citation

Ochoa, Victoria Norma, "Selection of chlorine tolerant E. coli O157:H7" (2005). ETD Collection for University of Texas, El Paso. AAI1427701.