Pathogenic potential of Shiga toxin-producing Escherichia coli strains of caprine origin: virulence genes, Shiga toxin subtypes, phylogenetic background and clonal relatedness

Abstract

BackgroundAll over the world, Shiga toxin-producing Escherichia coli (STEC) are considered as important zoonotic pathogens. Eight serogroups have the greatest role in the outbreaks and diseases caused by STEC which include O26, O45, O103, O111, O113, O121, O145 and O157. Ruminants, especially cattle are the main reservoirs but the role of small ruminants in the epidemiology of human infections has not been thoroughly assessed in many countries. The objective of this research was to investigate the pathogenic potential of the STEC strains isolated from slaughtered goats. In this study, a total of 57 STEC strains were recovered from 450 goats and characterized by subtyping of stx genes, O-serogrouping, phylo-typing and DNA fingerprinting.ResultsAmongst 57 STEC strains isolated from goats, the prevalence of stx1 was significantly more than stx2 (98.2% vs. 24.5%; P ≤ 0.05), and 22.8% of strains harbored both stx1 and stx2 genes. Three (5.2%) isolates were characterized as EHEC, which carried both eae and stx genes. A total of five stx-subtypes were recognized namely: stx1c (94.7%), stx1a (53.7%), stx2d (21%), stx2c (17.5%), and stx2a (15.7%). In some parts of the world, these subtypes have been reported in relation with severe human infections. The stx subtypes predominantly occurred in four combinations, including stx1a/stx1c (35%), stx1c (31.5%), stx1c/stx2a/stx2c/stx2d (5.2%) and stx1c/stx2c/stx2d (%5.2%). In serogrouping, the majority of STECs from goats did not belong to the top 8 serogroups but two strains belonged to O113, which has been recognized as an important pathogenic STEC in Australia. Interestingly, none of stx+eae+ isolates belonged to the tested serogroups. In phylo-typing the isolates mostly belonged to phylo-group B1 (82.4%), followed by phylo-group A (12.3%). STEC strains showed a substantial diversity in DNA fingerprinting; there were 24 unique ERIC-types (with a ≥95% similarity) among the isolates.ConclusionsDespite the fact that the top 8 STEC serogroups were uncommon in caprine strains, the presence of highly pathogenic stx subtypes indicates that small ruminants and their products can be considered as an overlooked public health risk for humans, especially in developing countries which consume traditional products.

Age related differences in phylogenetic diversity, prevalence of Shiga toxins, Intimin, Hemolysin genes and select serogroups of Escherichia. coli from pastured meat goats detected in a longitudinal cohort study

“…Goats six months and older were predominantly hosts to group B1. Our study findings are similar to [26,34,60] who found a high prevalence of the B1 group in adult goats and a few isolates of A phylogenetic group. Although the prevalence in individual species was not mentioned, Derakhshandeh et al [64] also found a predominance of group D E.coli in ruminants that included goats.…”

“…Our study also detected group B2 E. coli isolates mostly in kids less than six months with the highest number of isolates being detected around the weaning period. In the previous studies evaluating E.coli isolates from goats [26,34,60,61] only one reported a few isolates belonging to phylogenetic B2 [61]. E. coli isolates belonging to group A were very few in all age groups in this study.…”

“…Another study also found E.coli harboring virulence genes in goat milk and goat environment [35] and in Germany 75% of adult goats were found to harbor Stx1 positive E.coli which was higher than the other farm species in the study. In Iran virulence genes were detected in slaughter age goats [26] and also in US slaughter age goats [27].…”

“…Acknowledging the importance of STEC in public health, Europe now requires and emphasizes meat inspection efforts to ensure absence of STEC from slaughtered small ruminants [20]. Only a few studies have characterized prevalence of virulence genes in E.coli isolates from goats and sheep [21][22][23][24][25][26]. Moreover, prevalence of these important E. coli strains (STEC, EPEC) and their virulence gene profiles have not been investigated in US sheep and goat flocks despite the increasing number of meat goats in the US for the last decade and existence of several dairy goat flocks and also sheep flocks.…”

An investigation of shedding and super‐shedding of Shiga toxigenic Escherichia coli O157 and E. coli O26 in cattle presented for slaughter in the Republic of Ireland

“…Diversity in STEC phylogroups has been observed previously. A study of caprine-associated STEC predominantly observed phylogroup B1 isolates, with strains of phylogroup A also isolated (Jajarmi, Askari Badouei, Imani Fooladi, Ghanbarpour, & Ahmadi, 2018). A study of STEC in water used for shellfish production was identified as predominantly being of phylogoups A, B1 and D (Baliere et al, 2015), while a study of STEC in wildlife identified strains of phylogroups A, B1, B2 and D (Mora et al, 2012).…”