|MANDRELL, ROBERT - Former ARS Employee|
|Cooley, Michael - Mike|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2015
Publication Date: 12/4/2015
Citation: Carter, M.Q., Quinones, B., He, X., Louie, J.W., Zhong, W.W., Lee, B.G., Yambao, J.C., Mandrell, R.E., Cooley, M.B. 2015. An environmental shiga toxin-producing Escherichia coli O145 clonal population exhibits high-level phenotypic variation that includes virulence traits. Applied and Environmental Microbiology. doi: 10.1128/AEM.03172-15.
Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) serotype O145 is one of the major non-O157 serotypes associated with severe human disease. Numerous SETC O145 strains were isolated from Salina, California, a major produce production region in the US. We characterized the genetic makeup and the ability to express genes encoding key virulence traits in environmental strains and compared with the clinical strains linked to several outbreaks of enteric diseases in US and other countries. We found that genes encoding the key virulence traits identified in outbreak strains were highly conserved environmental strains, however, there was large variation in expression of virulence genes even among strains that were highly similar in their genetic makeup. Such traits included the production and cytotoxicity of Shiga toxin, the expression of hemolytic activity, and antibiotic resistance. Several cattle isolates exhibited comparable virulent traits with the O145 outbreak strains, suggesting that agricultural environments may serve as a source for the emergence of hyper virulent STEC strains.
Technical Abstract: 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 antibiotic resistance profile of environmental O145 strains isolated from a major produce-growing region in California. MLST analyses revealed that sequence type (ST) 78, a common ST in clinical strains, was the dominant genotype in environmental isolates. Mutations were detected in O-antigen genes, including nonsynomous and loss-of-function mutations. Analyses of fliC suggested that all environmental strains belonged to H28, a common serotype found in clinical strains. Regardless that the majority of environmental strains carry an intact fliC, only one strain retained swimming motility. Diverse stx genotypes were identified including stx1a, stx2a, stx2c and stx2e. Although no correlation was detected between the stx genotype and the Stx1 production, high abundance of Stx2 was detected mainly in strains carrying stx2a only, which was positively correlated with the cytotoxicity of O145 strains. Furthermore, all environmental strains were able to produce entero-hemolysin, however, only 10 strains were positive in anaerobic hemolytic activity (HlyE). Multi-drug resistance (MDR) appeared to be common as nearly half of O145 strains displayed resistance to at least two different classes of antibiotics. Distinct resistance profiles were observed in strains carrying same ST and virulence genes, implying a trend of clonal divergence. Our study suggests that, although the core virulence determinants of enterohemorrhagic E. coli are conserved in environmental O145 strains, there is large variation in expression of virulence traits even among strains that are genotypically highly related. Several cattle isolates expressed key virulent traits that were comparable with the O145 outbreak strains, emphasizing the emergence of hyper virulent STEC strains in agricultural environments.