Combined Effect of High-Pressure Treatments and Bacteriocin-Producing Lactic Acid Bacteria on Inactivation of
            <i>Escherichia coli</i>
            O157:H7 in Raw-Milk Cheese

Eva Rodriguez, Juan L. Arques, Manuel Nuñez, Pilar Gaya, Margarita Medina

doi:10.1128/aem.71.7.3399-3404.2005

<jats:title>ABSTRACT</jats:title> <jats:p> The effect of high-pressure (HP) treatments combined with bacteriocins of lactic acid bacteria (LAB) produced in situ on the survival of <jats:italic>Escherichia coli</jats:italic> O157:H7 in cheese was investigated. Cheeses were manufactured from raw milk inoculated with <jats:italic>E. coli</jats:italic> O157:H7 at approximately 10 <jats:sup>5</jats:sup> CFU/ml. Seven different bacteriocin-producing LAB were added at approximately 10 <jats:sup>6</jats:sup> CFU/ml as adjuncts to the starter. Cheeses were pressurized on day 2 or 50 at 300 MPa for 10 min or 500 MPa for 5 min, at 10°C in both cases. After 60 days, <jats:italic>E. coli</jats:italic> O157:H7 counts in cheeses manufactured without bacteriocin-producing LAB and not pressurized were 5.1 log CFU/g. A higher inactivation of <jats:italic>E. coli</jats:italic> O157:H7 was achieved in cheeses without bacteriocin-producing LAB when 300 MPa was applied on day 50 (3.8-log-unit reduction) than if applied on day 2 (1.3-log-unit reduction). Application of 500 MPa eliminated <jats:italic>E. coli</jats:italic> O157:H7 in 60-day-old cheeses. Cheeses made with bacteriocin-producing LAB and not pressurized showed a slight reduction of the pathogen. Pressurization at 300 MPa on day 2 and addition of lacticin 481-, nisin A-, bacteriocin TAB 57-, or enterocin AS-48-producing LAB were synergistic and reduced <jats:italic>E. coli</jats:italic> O157:H7 counts to levels below 2 log units in 60-day-old cheeses. Pressurization at 300 MPa on day 50 and addition of nisin A-, bacteriocin TAB 57-, enterocin I-, or enterocin AS-48-producing LAB completely inactivated <jats:italic>E. coli</jats:italic> O157:H7 in 60-day-old cheeses. The application of reduced pressures combined with bacteriocin-producing LAB is a feasible procedure to improve cheese safety. </jats:p>

Combined Effect of High-Pressure Treatments and Bacteriocin-Producing Lactic Acid Bacteria on Inactivation of <i>Escherichia coli</i> O157:H7 in Raw-Milk Cheese

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