Differences in virulence genes frequency among VTEC isolates from cattle, foods and environment

LUCCHESI, PAULA M. A.; KRÜGER, ALEJANDRA; PADOLA, NORA L.; ETCHEVERRÍA, ANALÍA I.; SANZ, MARCELO E.; FERNÁNDEZ, DANIEL; ALONSO, M.P.; POLIFRONI, ROSANA; ARROYO, GUILLERMO H.; PARMA, ALBERTO E.

Amsterdam

Congreso; 8th INTERNATIONAL SYMPOSIUM ON SHIGA TOXIN (VEROCYTOTOXIN)-PRODUCING Escherichia coli; 2012

Comité Internacional

Introduction & Objectives: The aims of this study were to asses the prevalent virulence genes and their combinations among a collection of VTEC isolates obtained from bovine cattle, foods and the environment, and to compare the results among isolates from different origins: calves, grown calves, adult cattle, foods and environment. Material & Methods:The isolates had been obtained from bovine cattle (451 isolates comprising: 95 from calves, 75 from grown calves, and 281 from adult cattle which include dairy cows, feedlot cattle and cattle at slaughter), meat (74 isolates) and the environment of dairy farms (20 isolates). They were characterized by a multiplex PCR that detects vt1,vt2, eae, ehxA and saa. Results:The vt2 gene was present in average in 85.1 % of the isolates, followed by ehxA and saa genes (63.7% and 35.6 %, respectively). When the isolates were grouped according to the origin, some marked differences in gene frequency were detected. The eae gene was detected in a high frequency in isolates from calves and the environment (74.7% and 65%, respectively), whereas the frequency was <15% in isolates from the other origins. The saa gene frequency showed an inverse trend, but never reached levels higher than 50%. The percentage of vt1-positive isolates was 40 among those from calves and the environment, and lower in the isolates from the other origins. The predominant virulence profiles, which comprised 78% of the isolates, were vt2, vt2/ehxA/saa, vt1/vt2/ehxA/saa, and vt2/eae/ehxA, arranged in decreasing order. Among calves, the profiles vt1/eae/ehxA and vt2/eae/ehxA were the most frequent,followed by vt2, and these three profiles also predominated among environmental VTEC isolates. The profile vt2 was the most frequent among grown calves, adult cattle and food isolates, followed by vt2/ehxA/saa and vt1/vt2/ehxA/saa. Conclusions: The frequencies of the genes detected in this study kept close similarity among isolates from meat, adult cattle and grown calves, differing from those from calves and the environment, which showed a higher frequency of eae and vt1 than the others. The relationship between VTEC isolates from meat and aduIt cattle is not unexpected as meat can become contaminated with VTEC during slaughter and the samples from adult cattle included cattle at slaughter and feedlot cattle that were near finishing. Besides it, on the other hand it can be speculated that young animals (calves)make an important contribution to the contamination of the environment in dairy farms.