Shiga toxin-producing Escherichia coli O26:H11 strains isolated from animal, food, and clinical sources in Argentina

KRÜGER A, LUCCHESI PM, SANSO AM, ETCHEVERRÍA A, BUSTAMANTE AV, FERNÁNDEZ D, BURGÁN J, FERNÁNDEZ L, LEOTTA G, ROSSEN JWA, PADOLA NL, FRIEDRICH AW.

Boston

Simposio; 9th International Symposium on Shiga Toxin (Verocytotoxin) producing Escherichia coli infections (VTEC2015).; 2015

Introduction: O26 is one of the most reported serogroups associated with severe human STEC infections worldwide. In order to contribute to the global characterization of STEC O26 strains, we have evaluated those circulating in Argentina between 1996 and 2013.Methods: Twenty nine STEC O26:H11 strains isolated from cattle, meat, human and farm environment were selected from different collections. Virulence profiles were determined with a commercial oligonucleotide microarray for E. coli (CLONDIAG Escherichia coli combined Assay, Alere Technologies GmbH, Germany). In addition, specific PCR reactions were performed to identify stx subtypes that could not be identified by the microarray assay. Strains were also characterised by an MLVA protocol comprising 9 VNTR loci.Results and Discussion: Stx-subtyping revealed the presence of either stx1a or stx2a, or both (only one isolate). Microarray results showed that strains also harbored genes encoding other toxins, adhesines, and components related to the type III secretion system. Regarding virulence profiles, three main clusters were identified: one included the stx1a-positive isolates, another the stx2a-positive isolates and the last one the stx1a/stx2a-positive isolate. The toxB, espI and katP genes were differentially distributed between stx1a-positive and stx2a-positive groups. Notably, all stx2a-positive strains had the same plasmid profile, positive for hlyA and espP, but negative for katP and etpD genes. MLVA typing divided the total number of strains into 19 distinct genotypes. Interestingly, major groups obtained by MLVA were similar to those obtained by the analysis of virulence factors.Implications: O26:H11 STEC strains circulating in our region including those isolated from cattle and meat harbor genes associated with high virulence, but differ from the emerging virulent clones circulating in Germany and France. Although strains harboring only the stx2a subtype have been rarely isolated from cattle and food in Europe, stx2a-positive strains are an important proportion of O26:H11 circulating in Argentina farms.