Verotoxins in bovine and meat verotoxin-producing Escherichia coli isolates: type, number of variants, and relationship to cytotoxicity

KRÜGER, A.; LUCCHESI, P.M.A.; PARMA, A.E.

APPLIED AND ENVIRONMENTAL MICROBIOLOGY

AMER SOC MICROBIOLOGY

Año: 2011 vol. 77 p. 73 - 79

0099-2240

In this study, we determined vt subtypes and evaluated verotoxicity in basal as well as in induced conditions of VTEC strains isolated from cattle and meat products. The vt2 gene (including all the vt2 variants) was present in the vast majority (87 %) of the 186 isolates studied. Moreover, the vt2 subtype, associated with serious disease, was present in 42 % of our VTEC collection. The other vt genes detected were vt1, vt1d, vt2vha, vt2vhb, vt2O118, vt2d (mucus activatable subtype) and vt2g. A total of 41 (22 %) of the isolates possessed more than one vt variant in its genome and among them, the most frequent combination was vt1/vt2 subtypes but we also observed multiple combinations among vt2 variants. Differences in verotoxicity titers were found among a selection of 54 isolates. Among isolates with a single vt2 variant, those carrying vt2 (E. coli EDL933 subtype) had high titers under both uninduced and induced conditions. However, the highest increase in cytotoxicity under mitomycin C treatment was detected among the strains carrying vt2vha or vt2hb variants. Notably, the isolates carrying vt1 (E. coli EDL933 subtype) showed a lower increase than most of the vt2-positive VTEC strains. Furthermore, the presence of more than one vt gene variant in the same isolate was not reflected in higher titers, and generally, they were lower than those of strains with only one gene variant. The main observation was that both basal and induced cytotoxic effects seemed to be associated with the type and number of vt variants more than the serotype or origin of the isolate.