Nisin treatment for inactivation of Salmonella species and other gram-negative bacteria

Nisin, produced by Lactococcus lactis subsp. lactis, has a broad spectrum of activity against gram-positive bacteria and is generally recognized as safe in the United States for use in selected pasteurized cheese spreads to control the outgrowth and toxin production of Clostridium botulinum. This study evaluated the inhibitory activity of nisin in combination with a chelating agent, disodium EDTA, against several Salmonella species and other selected gram-negative bacteria. After a 1-h exposure to 50 micrograms of nisin per ml and 20 mM disodium EDTA at 37 degrees C, a 3.2- to 6.9-log-cycle reduction in population was observed with the species tested. Treatment with disodium EDTA or nisin alone produced no significant inhibition (less than 1-log-cycle reduction) of the Salmonella and other gram-negative species tested. These results demonstrated that nisin is bactericidal to Salmonella species and that the observed inactivation can be demonstrated in other gram-negative bacteria. Applications involving the simultaneous treatment with nisin and chelating agents that alter the outer membrane may be of value in controlling food-borne salmonellae and other gram-negative bacteria.