An Environmental Shiga Toxin-Producing Escherichia coli O145 Clonal Population Exhibits High-Level Phenotypic Variation That Includes Virulence Traits

Abstract

b Shiga toxin-producing Escherichia coli (STEC) serotype O145 is one of the major non-O157 serotypes associated with severe human disease. Here we examined the genetic diversity, population structure, virulence potential, and antimicrobial resistance profiles of environmental O145 strains recovered from a major produce production region in California. Multilocus sequence typing analyses revealed that sequence type 78 (ST-78), a common ST in clinical strains, was the predominant genotype among the environmental strains. Similarly, all California environmental strains belonged to H28, a common H serotype in clinical strains. Although most environmental strains carried an intact fliC gene, only one strain retained swimming motility. Diverse stx subtypes were identified, including stx 1a , stx 2a , stx 2c , and stx 2e . Although no correlation was detected between the stx genotype and Stx1 production, high Stx2 production was detected mainly in strains carrying stx 2a only and was correlated positively with the cytotoxicity of Shiga toxin. All environmental strains were capable of producing enterohemolysin, whereas only 10 strains were positive for anaerobic hemolytic activity. Multidrug resistance appeared to be common, as nearly half of the tested O145 strains displayed resistance to at least two different classes of antibiotics. The core virulence determinants of enterohemorrhagic E. coli were conserved in the environmental STEC O145 strains; however, there was large variation in the expression of virulence traits among the strains that were highly related genotypically, implying a trend of clonal divergence. Several cattle isolates exhibited key virulence traits comparable to those of the STEC O145 outbreak strains, emphasizing the emergence of hypervirulent strains in agricultural environments.

Genome sequencing and comparative genomics of enterohemorrhagic Escherichia coli O145:H25 and O145:H28 reveal distinct evolutionary paths and marked variations in traits associated with virulence & colonization

“…Hence, the absence of iee accompanied by high IS copy numbers in O145:H25 and O165 suggests that IS transposition might be continuously depressed in those strains while being promoted in O145:H28 and the other EHEC strains. Furthermore, lower IS activity associated with decreased ability to change suggests that EHEC O145:H25 and O165 may not be able to adapt as rapidly to environmental changes as O145:H28 and other EHEC strains, which in turn might be one explanation why these serotypes are less commonly isolated [ 2 , 13 , 16 ]. Indeed, highly pathogenic and clinically relevant EHEC/STEC strains were found to carry iee and IS3 family members while less common EHEC/STEC strains were devoid of at least one of these elements [ 39 ].…”

“…EHEC O145 has emerged as one of the major EHEC serogroups involved in severe human disease worldwide [ 7 , 8 , 11 – 13 ]. Most clinical O145 isolates described in the literature encompass motile and nonmotile strains of serotype O145:H28 ( n > 150) [ 8 , 11 , 13 – 16 ], while EHEC O145:H25 appear to be less frequently isolated (10 reported cases) [ 11 , 13 , 17 , 18 ]. However, the majority of the documented EHEC O145:H25 isolates are associated with HUS ( n = 8), emphasizing the importance of this particular serotype [ 11 , 13 , 17 , 18 ].…”

“…In fact, the source of EHEC O145:H25 infections appears to be unknown, as O145:H25 have thus far only been isolated from humans. In contrast, ruminants, especially cattle have been shown to be natural reservoirs of O145:H28 and other EHEC strains [ 14 , 16 , 19 – 22 ] and the consumption of foods contaminated with ruminant feces such as meat and milk products, fresh produce or drinking water have been identified as important transmission routes for human EHEC infections [ 3 , 23 ]. It is not clear whether EHEC O145:H25 might be incapable of colonizing the bovine gut or have just failed to be isolated based on the sampling and detection methods applied.…”

Influence of Season and Feedlot Location on Prevalence and Virulence Factors of Seven Serogroups of Escherichia coli in Feces of Western-Canadian Slaughter Cattle

“…The diversity of stx genotypes present in non-O157 E . coli could possibly be due to diverse populations of Shiga toxin-encoding bacteriophages as suggested by Carter et al [ 34 ] in a survey of O145 isolated from cattle, wildlife, and the environment.…”

“…However, expression of E . coli virulence genes is variable [ 34 , 36 ] and further studies will be necessary to clarify relationships between virulence genes and human disease.…”