Phylogenetic analysis and Shiga toxin production profiling of Shiga toxin-producing/enterohemorrhagic Escherichia coli clinical isolates

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

BACKGROUND

All 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.

RESULTS

Amongst 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.

CONCLUSIONS

Despite 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.

Evaluation of a new chromogenic agar medium for detection of Shiga toxin-producing Escherichia coli (STEC) and relative prevalences of O157 and non-O157 STEC in Manitoba, Canada

This study assesses the detection performance of CHROMagar STEC medium relative to a reference cytotoxin assay and describes the current relative prevalence of O157 and non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes within the province of Manitoba, Canada. Over a 10-month period, 205 nonfrozen routine stool submissions to Cadham Provincial Laboratory (CPL) were used to assess the performance of CHROMagar STEC. Of the 205 stools, 14 were identified as true positives by a cytotoxin assay, with resultant CHROMagar STEC sensitivity, specificity, and positive predictive and negative predictive values of 85.7%, 95.8%, 60.0%, and 98.9%, respectively. Using a separate panel of 111 STEC strains, CHROMagar STEC was shown to support the growth of 96 (86.5%) isolates. To assess relative prevalence, attempts were made to isolate by any means all STEC strains identified at CPL over a 17-month period. Of 49 isolates (representing 86.0% of all STEC infections detected), only 28.6% were O157 STEC strains. Of the 35 non-O157 STEC strains, 29 were subjected to further molecular analysis. In contrast to earlier results from our area, carriage of stx(2) appears to have increased. Overall, although CHROMagar STEC is not recommended as a primary screen, our results indicate that it is an effective supplemental medium for the isolation of probable STEC strains. Increased isolation of these serotypes is warranted to better understand their prevalence, clinical characteristics, and epidemiology and aid in the development or enhancement of food safety control programs targeting all STEC serotypes.