CONICET | Buscador de Institutos y Recursos Humanos

Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen of global concern. The main reservoir for STEC is the bovine cattle, from which food, water and the environment can become contaminated. Lytic phages represent a promising alternative to control this threat throughout the food production chain. In this study, phages were isolated from bovine manure and effluents from two dairy farms. Samples were added to LB broth an incubated overnight for phage enrichment with the endogenous bacteria present in the samples. Then, culture supernatants were tested by the spot test for the presence of phages that could lyse STEC strains and, afterwards, phages were isolated and purified from the positive samples by the double agar method with E. coli DH5 as host strain. Nine native STEC strains representing different serotypes were used for analysis of phage host ranges. Phages were also preliminary evaluated for virulence traits performing a PCR screening for the gene encoding Shiga toxin 2 (stx2). Several phages that initially produced a lytic effect on O145:H- and O157:H7 STEC strains were either lost during purification stages on E. coli DH5or discarded because they rendered a positive PCR result for stx2. One of the purified phages, designated as ?L7.3?, was found to be lytic against O157:H7 STEC, rendering clear plaques on the STEC lawn, and was negative for stx2. This phage showed a higher EOP on E. coli DH5than on the native O157:H7 STEC strains tested and stability in SM buffer for at least 103 days at 4°C. Although more studies are needed to evaluate its performance and safety, the present results suggest that L7.3 phage could be a good preliminary candidate to use in STEC biocontrol.