Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2014
Publication Date: 8/8/2014
Publication URL: http://handle.nal.usda.gov/10113/59694
Citation: Tseng, M., Fratamico, P.M., Bagi, L.K., Delannoy, S., Fach, P., Manning, S., Funk, J. 2014. Molecular characterization of shiga toxin-producing E. coli (STEC) from finishing swine in a longitudinal study. Applied and Environmental Microbiology. DOI: 10.1128/AEM.01761-14. Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) represent a subset of E. coli that produce a toxin known as Shiga toxin (Stx) that damages human cells. STEC infections are associated with severe diseases in humans, including hemorrhagic colitis and the potentially fatal hemolytic uremic syndrome. STEC are attributed to more than 170,000 cases of human illness yearly in the U.S. Although cattle are considered important reservoirs for STEC, food products from other animal species, including pork products, have caused sporadic infections and outbreaks. However, little is known on the prevalence of STEC in clinically healthy swine, as well as the disease-causing potential of STEC strains carried by swine. Thus, the presence of a large panel of genes associated with STEC strains that cause illness in humans was examined in 150 STEC strains isolated from clinically healthy swine in the U.S. Based on the presence of specific genes, the strains were able to be categorized into three major pathogenic groups. Genes that are important in STEC strains that cause human illness were identified in the strains isolated from swine, thus certain swine STEC strains are potential human pathogens. Furthermore, one type of strain was prevalent among the swine housed in the same barn, indicating that STEC strains can easily spread among pigs that are kept in close proximity. The results enhance the understanding of the disease -causing potential of swine STEC and of the transmission dynamics of STEC among pigs, and thus provide information for risk assessments and for development of control strategies.
Technical Abstract: Shiga toxin-producing E. coli (STEC) infections are a critical public health concern because they can cause severe clinical outcomes, such as hemolytic uremic syndrome, in humans. Determining the presence or absence of virulence genes is essential in assessing the potential pathogenicity of STEC strains. Currently, there is limited information about the virulence genes carried by swine STEC strains; therefore, this study was conducted to examine the presence and absence of a large panel of virulence genes in STEC strains recovered previously from finishing swine in a longitudinal study. A subset of STEC strains was analyzed by pulsed field gel electrophoresis (PFGE) to examine their genetic relatedness. Swine STEC strains (n=150) were analyzed by a high-throughput real-time PCR array system, which included 69 virulence gene targets. Three major pathotypes consisted of sixteen different combinations of virulence gene profiles and serotypes were determined in the swine STEC strains. The majority of the swine STEC (n=120) belonged to serotype O59:H21 and carried the same virulence gene profile, which consisted of 9 virulence genes: stx2e, iha, ecs1763, lpfAO113, estIa (STa), ehaA, paa, terE, and ureD. The eae, nleF, and nleH1-2 genes were detected in one swine STEC strain (O49:H21). Other genes encoding adhesins, including iha, were identified (n=149). The PFGE results demonstrated that swine STEC strains from pigs raised in the same finishing barn were closely related. Our results revealed a diverse virulence gene content among the swine STEC population and enhance the understanding of the transmission dynamics of STEC among pigs in the same barn.