Comparative Study of the Antilisterial Activity of Nisin A and Pediocin AcH in Fresh Ground Pork Stored Aerobically at 5°C.

Listeria innocua strain Lin11 was used to compare the inhibitory activity of two bacteriocins (nisin A and pediocin AcH) in a decontamination process consisting of soaking artificially contaminated pieces of raw pork meat in a bacteriocin-containing solution before they were ground and stored aerobically at 5°C. Nisin A proved to be considerably more efficient than pediocin AcH, but generally after two days surviving bacteria in meat treated with each bacteriocin resumed growth at a rate similar to that of the control. Increasing the nisin concentration in the decontaminating bath resulted in greater loss of viability followed by regrowth of survivors. In addition, listeria cells surviving nisin action were found to have become resistant to nisin whereas survivors of pediocin AcH remained susceptible to this bacteriocin. The factors affecting bacteriocin activity in raw ground pork meat were then investigated. With the use of cold water and hot aqueous acid extraction to determine free (not bound) and total (bound to meat and free) bacteriocins, respectively, it was found that nisin was more stable than pediocin AcH. The loss of effectiveness, especially of pediocin AcH, was attributed to rapid degradation by meat proteases. It was concluded that nisin A is more appropriate than pediocin AcH for decontamination of this kind of meat but that routine use of nisin A at concentrations not high enough to eradicate all listerial cells could result in emergence of populations resistant not only to nisin A but to other bacteriocins.