Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 3, 2004
Publication Date: December 1, 2004
Citation: Fratamico, P.M., Bagi, L.K., Bush, E.J., Solow, B.T. 2004. Prevalence and characterization of shiga toxin-producing Escherichia coli in swine feces recovered in the national animal health monitoring system's swine 2000 study. Applied and Environmental Microbiology. v.70. P. 12. Interpretive Summary: A group of bacteria called Shiga toxin-producing Escherichia coli (STEC) cause disease in humans and animals, and animals such as cattle and swine are reservoirs of STEC. To determine the prevalence of harmful bacteria, including STEC, in swine in the U.S., the National Animal Health Monitoring System (NAHMS) Swine 2000 study was conducted by the USDA Animal and Plant Health Inspection Service with the collaboration of the Agricultural Research Service. Fecal samples collected from September 2000 to March 2001 from swine operations with 100 or more pigs from 13 of the top 17 swine-producing states were tested for the presence of STEC. Out of 687 total fecal samples tested, 70% (484/687) of the samples were positive using a polymerase chain reaction assay for toxin genes that have been associated with STEC that cause human illness. The serogroups of 219 of the isolated STEC bacteria were determined and found to include E. coli types or serogroups 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 untypable. Most of these E. coli serogroups have caused illness in swine or in humans. In addition, six fecal samples possessed two different STEC strains of different serogroups. It is noteworthy that no serogroup O157 isolates were recovered. Results of this study indicate that swine in the U.S. harbor STEC that can potentially cause illness in swine, as well as strains that may cause human illness. The extent to which swine play a role in the epidemiology of human infection, however, needs further investigation. Our studies provide information for the establishment of a database of STEC strains harbored by pigs in the U.S., which is necessary for the implementation of measures for disease prevention.
Technical Abstract: Shiga toxin-producing E. coli (STEC) comprise a serologically diverse group of organisms that cause disease in humans and animals. As part of the National Animal Health Monitoring System (NAHMS) Swine 2000 study, conducted by the USDA Animal and Plant Health Inspection Service with the collaboration of the Agricultural Research Service, one objective was to determine the prevalence of STEC in swine in the U.S. Fecal samples collected from U.S. swine operations from 13 of the top 17 swine-producing states from September 2000 to March 2001 were tested for the presence of STEC. Ten grams of swine feces were subjected to enrichment in tryptic soy broth, and then the samples were tested for the presence of stx1 and stx2 using the TaqManTM E. coli STX1 and STX2 PCR assays. Enrichments of samples positive for stx1 and/or stx2 were plated onto Luria Bertani agar, and colony hybridization was performed using digoxigenin-labeled probes for the stx1 and stx2 genes. Colonies hybridizing with the stx probe/s resulting in spots on the membranes were picked and confirmed by the PCR for the presence of the stx1, stx2, or stx2e genes, and the isolates were serotyped. Out of 687 total fecal samples tested, 54% (370/687), 64% (436/687), and 38% (261/687) were positive for stx1, stx2, or for both toxin genes, respectively, using the TaqMan E. coli STX1 and STX2 assays. Out of 219 isolates (from 213 TaqMan-positive samples) that were characterized, 29 produced stx1, 14 produced stx2, and 176 produced stx2e. Six fecal samples had isolates that possessed stx1 and also isolates that possessed stx2 or stx2e. 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 untypable. It is noteworthy that no serogroup O157 isolates were recovered. Results of this study indicate that swine in the U.S. harbor STEC that can potentially cause illness in swine, as well as strains that may cause human illness.