Prevalence and Characterization of Shiga Toxin-Producing Escherichia coli in Swine Feces Recovered in the National Animal Health Monitoring System's Swine 2000 Study

Abstract

ABSTRACT A study was conducted to determine the prevalence of Shiga toxin-producing Escherichia coli (STEC) in swine feces in the United States as part of the National Animal Health Monitoring System's Swine 2000 study. Fecal samples collected from swine operations from 13 of the top 17 swine-producing states were tested for the presence of STEC. After enrichment of swine fecal samples in tryptic soy broth, the samples were tested for the presence of stx 1 and stx 2 by use of the TaqMan E. coli STX1 and STX2 PCR assays. Enrichments of samples positive for stx 1 and/or stx 2 were plated, and colony hybridization was performed using digoxigenin-labeled probes complementary to the stx 1 and stx 2 genes. Positive colonies were picked and confirmed by PCR for the presence of the stx 1 , stx 2 , or stx 2e genes, and the isolates were serotyped. Out of 687 fecal samples tested using the TaqMan assays, 70% (484 of 687) were positive for Shiga toxin genes, and 54% (370 of 687), 64% (436 of 687), and 38% (261 of 687) were positive for stx 1 , stx 2 , and both toxin genes, respectively. Out of 219 isolates that were characterized, 29 (13%) produced stx 1 , 14 (6%) produced stx 2 , and 176 (80%) produced stx 2e . Twenty-three fecal samples contained at least two STEC strains that had different serotypes but that had the same toxin genes or included a strain that possessed stx 1 in addition to a strain that possessed stx 2 or stx 2e . The STEC isolates belonged to various serogroups, including O2, O5, O7, O8, O9, OX10, O11, O15, OX18, O20, O57, O65, O68, O69, O78, O91, O96, O100, O101, O120, O121, O152, O159, O160, O163, and O untypeable. It is noteworthy that no isolates of serogroup O157 were recovered. Results of this study indicate that swine in the United States harbor STEC that can potentially cause human illness.