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

Author:
Tomat, David, Casabonne, Cecilia, Aquili, Virginia, Balagué, Claudia, Quiberoni, Andrea
Source:
Food microbiology 2018 v.76 pp. 434-442
ISSN:
0740-0020
Subject:
Shiga toxin-producing Escherichia coli, anti-infective agents, bacteriophages, biological control, detection limit, enteropathogenic Escherichia coli, food matrix, foodborne illness, meat, milk, plate count, temperature, virulent strains
Abstract:
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 DH5α, 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 (2.2–2.8 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 (3.2–3.4 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, DH5α 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 (2.6–4.0 log10 CFU/mL) and 37 °C (3.0–3.8 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.
Agid:
6111365