First report of phages isolated from dairy farms in Argentina to control Shiga toxin producing Escherichia coli

ANA ELISA JUAREZ; STEFANIA BELEN PASCAL; ALEJANDRA KRÜGER; PAULA M. A. LUCCHESI

Oxford

Conferencia; Phages 2021 | Virtual Bacteriophage in Medicine, Food and Biotechnology 11th International Bacteriophage Meeting; 2021

Microbiology Society

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