Genomic Characterization of Bovine and Human Shiga toxin-producing Escherichia coli (STEC) in Israel: the One Health Approach

STEC is a foodborne pathogen of major public health importance. Cattle is the main animal reservoir of STEC and an important source of environmental and food contamination worldwide. This collaborative study applies whole genome sequencing (WGS) for analysis of STEC from human and bovine sources, with focus on phylogeny and zoonotic potential, virulence profiles and antimicrobial resistance.

In 2013, a nationwide screening in cattle was performed in the KVI in cooperation with the Koret School of Veterinary Medicine. Dairy and beef cattle (n=1,377) in 26 farms and quarantines were screened for STEC, showing a very high prevalence overall (62%). Prevalence was higher in dairy (65%) than in fattening farms (48%), and higher in younger animals. Data on STEC prevalence in humans is scarce, partly due to under-diagnosis and reporting. Notably, mandatory reporting is currently limited to serotype O157:H7. We analyzed a collection of human clinical isolates (hSTEC, 2009-2017, n=47) and a sample of veterinary isolates recovered from the cattle screening project (bSTEC, 2013-2014, n=91).

The predominant hSTEC type was O157:H7 ST11, with shiga toxin variants limited to stx1a, stx1c, stx2a, stx2c, while the bSTEC population displayed more diversity. The bovine strains included other potentially pathogenic EHEC not currently observed among clinical cases (O98:H21, O150:H2, O49:H10, O5:H9 and O172:H25). Among bSTEC 22% of isolates were typical Enterohemorrhagic E. coli, with O157:H7 accounting for 7% of bSTEC. wgMLST and wgSNP analyses indicated clonality among each serotype and within the O157:H7 population. STEC strains contained a variety of virulence factors as well as resistance genes predictive of phenotypes.

This first genomic study of the STEC population in Israel indicates EHEC and in particular E. coli O157:H7 are significant zoonotic pathogens linked to cattle. Further surveillance using whole genome sequence analysis should be implemented in order to support case investigation and veterinary and food control.