Shiga-toxin Escherichia coli O157:H7 strains isolated from humans in Argentina, Australia and New Zealand.

LEOTTA G.A., ; MILIWEBSKY E., ; CHINEN I., ; AZZOPARDI K.,; TENNANT S., ; ROBINS-BROWNE R., ; RIVAS M.

Melbourne, Australia.

Simposio; 6th International Symposium on Shiga Toxin (Verocytotoxin) - Producing Escherichia coli infections.; 2006

Shiga toxin-producing Escherichia coli (STEC) is an important emerging pathogen associated with different clinical manifestations such as bloody (BD) and non-bloody diarrhea (NBD), and hemolytic-uremic syndrome (HUS). E. coli O157:H7 is the most prevalent serotype. Argentina has the highest incidence of HUS in the world. The main aim of this study was to compare the phenotypic and genotypic characteristics of E. coli O157:H7 strains isolated from humans in Argentina, Australia and New Zealand and to establish their clonal relatedness. Seventy-three STEC O157:H7 strains, isolated from HUS (n=36), BD (n=19), NBD (n=11), and other non-specified diseases (n=7) in Argentina, Australia and New Zealand, were analyzed. The strains were identified by biochemical tests, EHEC-Hly production, serotyping and phage typing. A multiplex polymerase chain reaction (PCR) for the amplification of stx1, stx2 and rfbO157 genes was performed. The ehxA and eae genes were identified by PCR. A genotyping method, based on PCR-RFLP was performed to determine stx1 and stx2 variants. The clonal relatedness of strains was established by phage typing and XbaI-pulsed-field gel electrophoresis (PFGE). All strains were identified as E. coli O157:H7, and 72 strains were EHEC-Hly positive. The most frequent phage types identified in New Zealand, Argentinian, and Australian strains were PT2 (n = 15), PT49 (n = 11), and PT14 (n = 8), respectively. The most frequent stx genotypes were stx2/2vh-a (91%) in Argentina, stx2 only (89%) in New Zealand, and stx1/stx2 (55%) in Australia. All strains harbored the eae gene, and 72 (98.6%) strains harbored the ehxA gene. Forty-five different patterns were obtained by XbaI-PFGE. Thirty-seven strains were grouped in 10 clusters and 36 strains showed unique patterns. STEC strains isolated in Argentina, Australia, and New Zealand were different in terms of stx-genotype and phage type. Additionally, no common PFGE patterns were found in strains isolated in the three countries