Evaluation of a novel cocktail of six lytic bacteriophages against Shiga toxin-producing Escherichia coli in broth, milk and meat.

TOMAT, DAVID DAMIAN; CASABONNE, CECILIA; AQUILI, VIRGINIA; BALAGUE, CLAUDIA; QUIBERONI, ANDREA DEL LUJAN

FOOD MICROBIOLOGY

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 vol. 76 p. 434 - 442

0740-0020

Phages are potentially useful as antimicrobial agents in food, especially cocktails of different phages which may prevent the development of bacterial resistance. Biocontrol assays with a six-phage cocktail, which is lytic against DH5á, an enteropathogenic (EPEC) and two Shiga-toxigenic (STEC) Escherichia coli strains, were performed in Hershey-Mg broth, milk and meat at refrigerated (4°C), room (24°C) and abusive (37°C) temperatures. At 4°C, cell counts were significantly lower (2.2 to 2.8 log10 CFU/mL) when E. coli strains (~ 109 CFU/mL) were challenged against the phage cocktail (~ 109 PFU/mL) in Hershey-Mg broth after 24 h. However, reductions were higher (3.2 to 3.4 log10 CFU/mL) after a 48 h exposure for all the strains tested. In addition, reduction values reached up to 3.4 log10 CFU/mL (24°C) and 3.6 log10 CFU/mL (37°C) in challenge tests after 24 h, though the reductions achieved were slightly lower after 48 h for the four E. coli strains tested. In milk, the cocktail was highly effective since bacterial counts were below the detection limit (< 101 CFU/mL) at 4°C, while the reductions ranged from 2 to 4 log10 CFU/mL at 24°C after a 24 h exposure. At 37°C, DH5á was eliminated within 2 h, and an average cell decrease of 4 log10 CFU/mL was observed for the three pathogenic strains tested. When the assays were performed in meat, biocontrol values ranged from 0.5 to 1.0 log10 CFU/mL after 48 h at 4°C, while a higher cell inactivation was achieved at 24°C (2.6 to 4.0 log10 CFU/mL) and 37°C (3.0 to 3.8 log10 CFU/mL). Furthermore, higher inactivation values for O157:H7 STEC (1.55 ± 0.35 log10 CFU/mL) at 4°C were obtained in meat when incubation was extended up to 6 days. As a conclusion, our six-phage cocktail was highly effective at 24°C and 37°C, though less effective at 4°C in both food matrices evaluated. Thus, it might be applied against pathogenic EPEC and STEC strains to prevent foodborne diseases especially when the cold chain is lost.