Genetic diversity asessment of VTEC O91 in Argentina

Abstract

VTEC O91 has ranked in the top five of the non-O157 serogroups most frequently associated with human cases. In order to gain insight into the genetic diversity of O91 VTEC strains isolated in Argentina we analyzed their virulence properties and carried out a multiple-locus variable-number tandem repeats analysis (MLVA). Methods We tested a panel of 21 virulence genetic markers associated with human and animal infections and determined the relatedness by an MLVA assay comprising 9 VNTR loci. Twenty-two VTEC O91 isolated from cattle and meat food in Argentina and belonging to 5 serotypes (O91:H21, O91:H8, O91:H14, O91:H28, O91:H40) were studied.Results Eight virulence profiles were obtained for the O91 VTEC strains: 4 for O91:H21 + O91:H8 + O91:H14 + O91:H28 + O91:H40. All strains contained ehxA and lpfA0113 genes and only both vtx1-positive strains lacked saa, which encodes the STEC autoagglutinating adhesin. Other genes involved in adhesion were detected: ehaA (91%), elfA and espP (86%), ecpA (82%) and, hcpA (77%). Nine virulence genes were never detected in the studied isolates. The gene encoding the cytolethal distending toxin type-V (CDT-V) was found only in O91:H8 and O91:H21, being present in the majority (89%) of strains of this last serotype. MLVA typing divided the total number of strains into 12 distinct genotypes, and 9 of them were unique to a single strain.Conclusions No association was observed between the virulence profiles and the source of the strains. Strains of different serotypes within the O91 serogroup differed by the spectrum of putative virulence genes. Although they lack the eae gene, most of the strains have the genetic potential to adhere to host cells through other structures and possess the cdt-V gene, which has been found in VTEC strains involved in serious diseases. MLVA showed clonal relatedness among strains isolated from cattle belonged to a same dairy farm and, on the other hand, suggests the need to increase the number of VNTR loci which could allow a higher discrimination among isolates. We conclude that VTEC O91 isolates from Argentina can group in different lineages that differ by virulence factors, with accumulation of virulence determinants in the O91:H21 serotype.