Survival of enterohemorrhagic Escherichia coli O157:H7 in water

Several recent Escherichia coli O157:H7 outbreaks associated with both drinking and recreational water raise concerns about waterborne illness caused by this pathogen. The survival characteristics of a mixture of five nalidixic acid-resistant E. call O157:H7 strains (10(3) CFU/ml) in filtered and autoclaved municipal water, in reservoir water, and in water from two recreational lakes were determined for a period of 91 days at 8, 15, or 25 degrees C. Greatest survival was in filtered autoclaved municipal water and least in lake water. Regardless of the water Source, survival was greatest at 8 degrees C and least at 25 degrees C, E, coli O157:H7 populations decreased by 1 to 2 log(10) by 91 days at 8 degrees C, whereas the pathogen was not detectable (greater than or equal to 3 log(10) decrease) within 49 to 84 days at 25 degrees C in three of the four water sources. SDS-PAGE of surface antigens of surviving cells revealed that there was no major alteration in lipopolysaccharide pattern, but outer membrane protein composition did change. These studies indicate that E, coli O157:H7 is a hardy pathogen that can survive for long periods of time in water, especially at cold temperatures. However, direct viable counts of E. coli O157:H7 determined by acridine orange staining remained essentially the same for 12 weeks at 25 degrees C, whereas viable counts on tryptic soy agar plates decreased to undetectable levels within 12 weeks. Results suggest that E. coli O157:H7 can enter a viable but nonculturable (VBNC) state in water.