Differential Survival of Shiga-Toxigenic Escherichia coli in Simulated Runoff.

Shiga-toxigenic Escherichia coli (STEC) are a group of zoonotic pathogens associated with cattle manure. Seven STEC serotypes have been identified as a particular concern for public health. While STEC are primarily considered foodborne pathogens, numerous outbreaks in multiple states have been attributed to environmental exposure. We know that there are differences in biochemistry between different E. coli serotypes, and previous research by other laboratories has demonstrated variability in survival among generic E. coli in the environment. In this study, we examined the long-term survival of seven STEC serotypes in simulated runoff. Dried manure and soil were mixed together at the agronomic rate for phosphorus, and added to sterile distilled water. Overnight cultures of the seven serotypes were inoculated at a standard rate, and aliquots were plated for enumeration at Days 1, 2, 7, 14, 21, 36, and 42, and monthly thereafter for one year. Bacteria were enumerated using culture plates, with confirmation by PCR, and the entire experiment was repeated in sequential years. STEC O26 and STEC O45 were initially enriched upon inoculation into the simulated runoff, and remained viable for the duration of the experiment, and trials for year one remained viable at 30 months when the testing for year two was concluded. STEC O111, O121, and O145 declined rapidly upon inoculation, and were all undetectable by PCR by month 11. Survival of STEC O157 and STEC 103 were similar to each other in both years, but did not show a consistent year-to-year survival pattern. These laboratory studies suggest that there may be serotype-specific survival patterns among STEC, and demonstrate the biological potential for STEC to survive for extended periods of time in manure-impacted matrices.