Research – Prevalence and patterns of fecal shedding of Shiga toxin–producing Escherichia coli by cattle at a commercial feedlot in South Africa

Wiley Online

Healthy colonized cattle are the major reservoir of Shiga toxin–producing Escherichia coli (STEC) and play a key role in the entry point of the pathogen into the beef chain. Excretion rates and the concentration of the pathogen in feces influence the epidemiology and transmission of the pathogen within herds and to humans. This study evaluated the prevalence and dynamics of fecal shedding of STEC by cattle in a commercial feedlot in Gauteng, South Africa. An initial cross-sectional survey was conducted; fecal samples were obtained from 106 randomly selected weaned beef calves on arrival at the feedlot using polymerase chain reaction (PCR) to screen by detecting stx1 and stx2 genes. Subsequently, a longitudinal study was conducted, and 15 STEC-positive and 11 STEC-negative cattle were sampled monthly and followed to slaughter. STEC O157 and non-O157 were enumerated in samples using commercial chromogenic agar. Initial prevalence of STEC shedding was 27% (29/106; 95% CI [19, 37%]). All 26 cattle shed STEC intermittently or continuously during the study period, all except one were super-shedders (≥4 log10 CFU/g) at one or more samplings, and 19 (73%) were persistent or intermittent super-shedders. Of the 38 STEC isolates recovered, 15 (39%) were serotypeable, representing 11 non-O157 serogroups, including O101, O168, O178, and O68. The most frequent virulence combination profile was stx1 + eaeA + ehxA (n = 12; 32%). This study confirms the occurrence and variability of STEC super-shedding in feedlot cattle and highlights that super-shedding is not limited to STEC O157. It also shows their public health significance.

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