Abstract
Non-O157 STEC are increasingly linked to foodborne infections, yet little is known about the diversity and molecular epidemiology across locations. Herein, we used whole genome sequencing to examine genetic variation in 894 isolates collected from Michigan patients between 2001 and 2018. In all, 67 serotypes representing 69 multilocus sequence types were identified. Serotype diversity increased from an average of four (2001–2006) to 17 (2008–2018) serotypes per year. The top six serogroups reported nationally caused > 60% of infections in 16 of the 18 years; serogroups O111 and O45 were associated with hospitalization as were age ≥ 65 years, diarrhea with blood and female sex. Phylogenetic analyses of seven multilocus sequence typing (MLST) loci identified three clades as well as evidence of parallel evolution and recombination. Most (95.5%) isolates belonged to one clade, which could be further differentiated into seven subclades comprising isolates with varying virulence gene profiles and serotypes. No association was observed between specific clades and the epidemiological data, suggesting that serogroup- and serotype-specific associations are more important predictors of disease outcomes than lineages defined by MLST. Molecular epidemiological studies of non-O157 STEC are important to enhance understanding of circulating strain distributions and traits, genetic variation, and factors that may impact disease risk and severity.
Highlights
Non-O157 Shiga toxin-producing Escherichia coli (STEC) are increasingly linked to foodborne infections, yet little is known about the diversity and molecular epidemiology across locations
Other virulence genes such as eae and ehxA, have been linked to p athogenicity8,11. eae is found on the locus of enterocyte effacement (LEE) pathogenicity island, which mediates attachment and effacement of intestinal epithelial cells[12] and ehxA is located on distinct plasmids. ehxA has been identified in strains from patients, animals, 1Department of Microbiology and Molecular Genetics, Michigan State University, 1129 Farm Lane, East Lansing, MI 48824, USA. 2Michigan Department of Health and Human Services, Bureau of Laboratories, Lansing, MI 48906, USA. 3Michigan Department of Agriculture and Rural Development, East Lansing, MI 48823, USA. *email: mannin71@msu.edu
Over the 18-year period, 1,060 non-O157 STEC case reports were recorded in the Michigan Disease Surveillance System (MDSS), the online communicable disease reporting system for notifiable infections
Summary
Non-O157 STEC are increasingly linked to foodborne infections, yet little is known about the diversity and molecular epidemiology across locations. Molecular epidemiological studies of non-O157 STEC are important to enhance understanding of circulating strain distributions and traits, genetic variation, and factors that may impact disease risk and severity. Seven stx[2] subtypes have been identified; stx[2] (a-g), stx2a and stx2d were linked to more severe infections[8,9], while stx2e, stx2f., and stx2g were more common in environmental sources and a nimals[10] Other virulence genes such as eae (intimin) and ehxA (enterohemolysin), have been linked to p athogenicity. Environmental samples[13,14] Examining these genes in clinical isolates can help identify combinations linked to severe disease, monitor changes in gene frequencies, and understand STEC evolution. Examining trends in specific geographic locations can enhance understanding of epidemiology, virulence, and evolution and help guide public health interventions strategies
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