Prevalence and concentration of stx+ E. coli and E. coli O157 in bovine manure from Florida farms

Abstract

Fresh produce outbreaks due to Shiga toxin-producing Escherichia coli (STEC) continue to occur in the United States (US). Manure-amended soils can pose a public health risk when used for growing raw agricultural commodities. Knowing the prevalence and concentration of STEC in untreated biological soil amendments of animal origin (BSAAO) is important to help guide the most appropriate pre-harvest interval(s) following application to limit risks from these soil amendments. Bovine manure samples were collected from 12 farms in Florida, including samples from piles, lagoons, barns, and screened solids. Two methods were used to detect stx1 / 2 and rfbE genes in samples. A prevalence rate of 9% for stx1 and/or stx2 and 19% for rfbE was observed from the 518 bovine manure samples evaluated. A most probable number (MPN) assay was performed on stx + samples when applicable. The geometric mean for stx+ samples (n = 20) was 3.37 MPN g -1 (0.53 log MPN g -1 ) with a maximum value of 6,800 MPN g -1 (3.83 log MPN g -1 ). This research was part of a larger nationwide geographical study on the prevalence and concentration of STEC in bovine manure to help guide regulations on feasible pre-harvest intervals for the application of untreated BSAAO.

Survival of Escherichia coli O157 in autoclaved and natural sandy soil mesocosms

“…The E. coli O157 strains used in this study have distinct stx-profiles (stx1+/stx2+ (6DL-17), stx1-/stx2-(5DOE-2), and stx1-/stx2+ (9OLM-10) and were obtained from bovine manure in Florida during previous research [27]. Cultures were streaked for isolation from cryovials onto tryptic soy agar (Difco, Sparks, MD) supplemented with 80 mg L -1 rifampin (Thermo Fisher Scientific, Fair Lawn, NJ) (TSAR) and incubated at 37˚C for 24 h. An isolated colony was transferred to 10 mL of tryptic soy broth (Difco) supplemented with 80 mg L -1 rifampin (TSBR) and incubated at 37˚C for 18 h, 100 rpm.…”

Single-Cell-Based Digital PCR Detection and Association of Shiga Toxin-Producing Escherichia coli Serogroups and Major Virulence Genes

“…Diluting samples to an appropriate range of template concentrations is also critical for generating suitable dPCR signals for accurate gene association analysis. Concentrations of STEC in most cattle feces range from 10 1 to 10 3 CFU/g (43,44). Our data indicated that enrichment overnight will increase the concentration by 10 3 -to 10 4 -fold, and the marginally detectable concentration for real-time PCR assays is about 5 ϫ 10 3 CFU/g (13,14).…”

Escherichia coli O157 survival in liquid culture and artificial soil microcosms with variable pH, humic acid and clay content

“…The E. coli O157 stx1 +/ stx2 + strain used in this study was isolated from a previous bovine manure study (Baker et al . 2019), and was made rifampin resistant. This strain has shown to exhibit similar survival rates as E. coli O157 strains with different stx profiles (Baker et al .…”