Comparison of the distribution of virulence factors in eae-negative Shiga toxin-producing Escherichia coli strains isolated from cattle and humans in Argentina.

GALLI L., LEOTTA G.A., IRINO K., RIVAS M.

Buenos Aires

Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin) - Producing Escherichia coli infections.; 2009

Shiga toxin-producing Escherichia coli (STEC) strains can cause a broad spectrum of human diseases. Some STEC strains harbor a pathogenicity island, the locus of enterocyte effacement (LEE), required to promote attaching and effacing lesions. However, several STEC strains have been characterised as eae-negative, indicating that the LEE is not essential for pathogenesis. Additional virulence factors encoded outside the LEE were identified and proposed to play a role in pathogenesis including: Lpf, Iha, Saa, EHEC-Hly, Efa1, East1 and type I fimbriae. The aim of this study was to establish the prevalence of virulence factors that are not encoded in the LEE region, in eae-negative STEC strains of different serotypes isolated from Argentine cattle, compared to those isolated from humans, by PCR. A total of 200 STEC strains isolated from humans (n=47, 23.5%) and cattle (n=153, 76.5%) were studied. All the strains were randomly selected and tested for XbaI enzyme digestion patterns by pulsed-field gel electrophoresis, obtaining 117 patterns and 26 clusters. Based on the selection criteria established, all the strains were eae-negative and sorbitol fermenting. The ehxA gene was carried by 54% of the strains studied (56.8% cattle, 44.7% humans). From those 108 ehxA-positive strains, 100 were also saa-positive. Interestingly, there were no ehxA-negative strains but saa-positive. All the strains studied carried at least one virulence factor gene. Of the 47 strains isolated from humans, 46 (97.9%) carried the gene lpfAO113, 42 (89.4%) carried iha, 19 (40.4%) carried saa, and 5 (10.6%) carried astA. All the cattle strains studied (100%) carried the gene lpfAO113, 130 (84.9%) carried iha, 81 (52.9%) carried saa, and 15 (9.8%) carried astA. The gene efa1 was not identified among the strains studied, which is consistent with previous studies that described efa1 more frequently in eae-positive strains. The most prevalent virulence factor identified among all the STEC strains studied were those encoded by lpfAO113 (99.5%) and iha (86%). Additionally, fimA was studied. The presence of fimA was identified in 92.8% of cattle strains and 95.7% of human strains. Of note, negative fimA strains (11/200, 5.5%) were stx1 and astA positive, except one clinical strain that was stx2 and astA negative, and another clinical isolate that was stx2, and the only virulence factor detected was iha. A diversity of virulence profiles was observed among STEC strains, but the most prevalent profile observed among STEC strains isolated from humans was lpfAO113/iha/fimA, whereas lpfAO113/iha/saa/ehxA/fimA prevailed among STEC strains isolated from cattle belonging to 16 different serogroups, with O113, O116, O130 and O178 being the most prevalent ones. Due to the high frequency of detection of lpfAO113 and iha in eae-negative STEC strains associated to illness in humans, it is possible to hypothesize that these genes may play a role in pathogenesis. This finding is important because those adhesins are also the most prevalents in cattle, recognized as the main reservoir of STEC strains.