Prevalence, virulence potential, and pulsed-field gel electrophoresis profiling of Shiga toxin-producing Escherichia coli strains from cattle

Background: As a primary source of Shiga-toxin-producing Escherichia coli (STEC) infection, cattle are often targeted to develop strategies for reducing STEC contamination. Monitoring the virulence potentials of STEC isolates from cattle is important for tracing contamination sources, managing outbreaks or sporadic cases, and reducing the risks for human infection. This study aimed to investigate the prevalence of STEC in cattle farm samples in South Korea and to assess their virulence potentials. Results: In total, 63 STEC were isolated from 496 cattle farm samples, and temperature and rainfall affected STEC prevalence (p < 0.001). The 0157 serogroup was most prevalent, followed by 0108, 08, 084, 015, and 0119. In the stx variant test, high prevalence of stx2a and stx2c (known to be associated with high STEC virulence) were observed, and stx2g, a bovine STEC variant, was detected in STEC 015 and 0109. Additionally, stx1c was detected in eae-positive STEC, suggesting genetic dynamics among the virulence genes in the STEC isolates. STEC non-0157 strains were resistant to tetracycline (17.9%), ampicillin (14.3%), and cefotaxime (3.6%), while STEC 0157 was susceptible to all tested antimicrobials, except cefotaxime. The antimicrobial resistance genes, bla(TEM) (17.5%), tetB (6.3%), and tetC (4.8%), were only detected in STEC non-0157, whereas tetE (54.0%) was detected in STEC 0157. AmpC was detected in all STEC isolates. Clustering was performed based on the virulence gene profiles, which grouped STEC 084, 0108, 0111, and 0157 together as potentially pathogenic STEC strains. Finally, PFGE suggested the presence of a prototype STEC that continues to evolve by genetic mutation and causes within-and between-farm transmission within the Gyeonggi province. Conclusions: Considerable numbers of STEC non-0157 were isolated from cattle farms, and the virulence and antimicrobial resistance features were different between the STEC 0157 and non-0157 strains. STEC from cattle with virulence or antimicrobial resistance genes might represent a threat to public health and therefore, continual surveillance of both STEC 0157 and non-0157 would be beneficial for controlling and preventing STEC-related illness.