Fate of generic and Shiga toxin-producing Escherichia coli (STEC) in Central Florida surface waters and evaluation of EPA Worst Case water as standard medium.

Agricultural water is considered as one of the main contamination source for produce prior to harvest. The purpose of study was to evaluate the fate of Shiga toxin-producing Escherichia coli (STEC), and generic E. coli in Central Florida agricultural surface water at different temperatures and the potential use of EPA Worst Case water as a standardized media. Cocktails of STEC (O145, O104, O111, O103, O157), and generic E. coli K-12 were inoculated into agricultural surface water samples (non-sterile and sterilized) and EPA Worst Case water, and enumerated for up to 168 days. E. coli was held at 15 and 25 ± 1 °C. Tested microorganisms decreased most rapidly in non-sterile surface water. At day 168, E. coli populations decreased to ≤2.5 log CFU/100 ml in non-sterile surface water and were 4.8 ≤ and ≤ 8.5 log CFU/100 ml in sterile surface water and EPA Worst Case water. Populations were significantly (P ≤ .05) higher in sterile surface water and EPA Worst Case water at all sampling points starting from Day 28. Rate of declines in non-sterile surface waters were between 32.8 and 50 days at both tested temperatures and microorganisms. Addition of cycloheximide to non-sterile surface waters resulted in no significant effect on behavior of E. coli populations. Monitoring generic E. coli (represented by K-12) population changes is a reasonable indicator of STEC survival in agricultural water. EPA Worst Case water is a suitable standard control for surface water microcosms.