Occurrence, Serotypes and Virulence Characteristics of Shiga-Toxin-Producing Escherichia coli Isolates from Goats on Communal Rangeland in South Africa

Shiga-toxin-producing Escherichia coli is a foodborne pathogen commonly associated with human disease characterized by mild or bloody diarrhea hemorrhagic colitis and hemolytic uremic syndrome. This study investigated the occurrence of STEC in fecal samples of 289 goats in South Africa using microbiological culture and PCR. Furthermore, 628 goat STEC isolates were characterized by serotype (O:H) and major virulence factors by PCR. STEC was found in 80.2% (232/289) of goat fecal samples. Serotyping of 628 STEC isolates revealed 63 distinct serotypes including four of the major top seven STEC serogroups which were detected in 12.1% (35/289) of goats: O157:H7, 2.7% (8/289); O157:H8, 0.3%, (1/289); O157:H29, 0.3% (1/289); O103:H8, 7.6% (22/289); O103:H56, 0.3% (1/289); O26:H2, 0.3% (1/289); O111:H8, 0.3% (1/289) and 59 non-O157 STEC serotypes. Twenty-four of the sixty-three serotypes were previously associated with human disease. Virulence genes were distributed as follows: stx1, 60.6% (381/628); stx2, 72.7% (457/628); eaeA, 22.1% (139/628) and hlyA, 78.0% (490/628). Both stx1 and stx2 were found in 33.4% (210/628) of isolates. In conclusion, goats in South Africa are a reservoir and potential source of diverse STEC serotypes that are potentially virulent for humans. Further molecular characterization will be needed to fully assess the virulence potential of goat STEC isolates and their capacity to cause disease in humans.

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.

Characterization of Shiga Toxin Subtypes and Virulence Genes in Porcine Shiga Toxin-Producing Escherichia coli

Similar to ruminants, swine have been shown to be a reservoir for Shiga toxin-producing Escherichia coli (STEC), and pork products have been linked with outbreaks associated with STEC O157 and O111:H-. STEC strains, isolated in a previous study from fecal samples of late-finisher pigs, belonged to a total of 56 serotypes, including O15:H27, O91:H14, and other serogroups previously associated with human illness. The isolates were tested by polymerase chain reaction (PCR) and a high-throughput real-time PCR system to determine the Shiga toxin (Stx) subtype and virulence-associated and putative virulence-associated genes they carried. Select STEC strains were further analyzed using a Minimal Signature E. coli Array Strip. As expected, stx_2e (81%) was the most common Stx variant, followed by stx_1a (14%), stx_2d (3%), and stx_1c (1%). The STEC serogroups that carried stx_2d were O15:H27, O159:H16 and O159:H-. Similar to stx_2a and stx_2c, the stx_2d variant is associated with development of hemorrhagic colitis and hemolytic uremic syndrome, and reports on the presence of this variant in STEC strains isolated from swine are lacking. Moreover, the genes encoding heat stable toxin (estIa) and enteroaggregative E. coli heat stable enterotoxin-1 (astA) were commonly found in 50 and 44% of isolates, respectively. The hemolysin genes, hlyA and ehxA, were both detected in 7% of the swine STEC strains. Although the eae gene was not found, other genes involved in host cell adhesion, including lpfA_O113 and paa were detected in more than 50% of swine STEC strains, and a number of strains also carried iha, lpfA_O26, lpfA_O157, fedA, orfA, and orfB. The present work provides new insights on the distribution of virulence factors among swine STEC strains and shows that swine may carry Stx1a-, Stx2e-, or Stx2d-producing E. coli with virulence gene profiles associated with human infections.

Preliminary virulence genotyping and phylogeny of Escherichia coli from the gut of pigs at slaughtering stage in Brazil

In the current study we screened Escherichia coli from intestine of pigs slaughtered in Mato Grosso, Brazil, for virulence-markers related to human disease. Furthermore, we employed for the first time a phylogenetic assay to explore the association between phylogeny and virulence genotype in E. coli from finished swine. A low prevalence (7.8%) of E. coli harbouring virulence genes was observed. Among the positive isolates, 3.3% could be classified as atypical EPEC, 2.2% as STEC and 2.2% as CDT harbouring E. coli. Virulence genes were not found to co-occur in a strain. Phylogenetic determination of isolates revealed a low prevalence of E. coli lineages related to disease. Therefore, preliminary sampling of 74 pigs indicated that slaughter swine may not be major reservoirs of E. coli capable of causing human disease. In light of the significant association between phylogeny and virulence genotype, we also underscored the phylogenetic grouping of strains as a valuable tool for E. coli surveillance programmes in slaughterhouses.

Subtilase cytotoxin-coding genes in verotoxin-producing Escherichia coli strains from sheep and goats differ from those from cattle

Subtilase cytotoxin (SubAB) from verotoxin (VT)-producing Escherichia coli (VTEC) strains was first described in the 98NK2 strain and has been associated with human disease. However, SubAB has recently been found in two VT-negative E. coli strains (ED 591 and ED 32). SubAB is encoded by two closely linked, cotranscribed genes (subA and subB). In this study, we investigated the presence of subAB genes in 52 VTEC strains isolated from cattle and 209 strains from small ruminants, using PCR. Most (91.9%) VTEC strains from sheep and goats and 25% of the strains from healthy cattle possessed subAB genes. The presence of subAB in a high percentage of the VTEC strains from small ruminants might increase the pathogenicity of these strains for human beings. Some differences in the results of PCRs and in the association with some virulence genes suggested the existence of different variants of subAB. We therefore sequenced the subA gene in 12 strains and showed that the subA gene in most of the subAB-positive VTEC strains from cattle was almost identical (about 99%) to that in the 98NK2 strain, while the subA gene in most of the subAB-positive VTEC strains from small ruminants was almost identical to that in the ED 591 strain. We propose the terms subAB1 to describe the SubAB-coding genes resembling that in the 98NK2 strain and subAB2 to describe those resembling that in the ED 591 strain.