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Escherichia coli O26:H11 growth in co-culture with an antagonistic strain of Hafnia alvei according to pH and temperature

Callon, Cécile, Ndob, Aïchatou Musavu, Savignard, Amaury, Rifa, Etienne, Montel, Marie-Christine
Food control 2016 v.62 pp. 117-124
Escherichia coli O26, Hafnia alvei, adverse effects, analysis of variance, cheesemaking, cheeses, coculture, experimental design, mathematical models, pH, prediction, starter cultures, temperature
This study examines the combined effects of temperature (33 °C, 27 °C, 22 °C, 18 °C) and pH (5.3, 5.8, 6.3, 6.8), within the range of values encountered during cheese-making, on the growth of an Escherichia coli O26:H11 strain (21765) co-cultivated with an antagonistic strain of Hafnia alvei (B16) at different initial concentrations (4, 5, 6, 7 Log CFU/mL). Experimental designs including these parameters were applied to a liquid medium (Brain Heart Infusion) and to uncooked pressed model cheeses. In both these environments, the polynomial models gave a good prediction of E. coli O26:H11 levels after 6–24 h of incubation. In both predictive models, ANOVA analysis showed that temperature and pH both had a major positive effect on the level of E. coli O26:H11 at 6 h and the initial concentration of H. alvei had a negative effect. In BHI medium and in uncooked pressed model cheese at 24 h, temperature had a weaker positive effect when B16 was inoculated at 7 Log rather than 5 Log CFU/mL. In cheese at 24 h, pH also had a more marked positive effect on E. coli O26:H11 levels when H. alvei was inoculated at 7 Log. The predictive model established in BHI gave a good prediction of the levels of E. coli O26:H11 in uncooked pressed cheeses at 6 h but overestimated them at 24 h. H. alvei B16 inoculation at 7 Log CFU/mL associated with pH 5.3 and a temperature of 22 °C may help to control E. coli O26:H11 at 24 h in cheeses. Further studies with cheese production will be necessary to manage pH (via starter culture) in combination with temperature, without modifying the sensorial qualities of the cheese.