Enhanced inactivation of Salmonella typhimurium and verotoxigenic Escherichia coli by nisin at 6.5 degree C

• Published in: Food microbiology Vol. 16; no. 3; pp. 257 - 267
• Main Authors: Elliason, D J, Tatini, SR
• Format: Journal Article
• Language: English
• Published: 01.06.1999
• Subjects: Escherichia coli; Salmonella typhimurium
• ISSN: 0740-0020

While the use of natural antimicrobials such as nisin is useful to inhibit and/or inactivateListeria monocytogenes, Bacillus cereus and Clostridium botulinum , it is not effective on Salmonella and Escherichia coli , presumably due to the inaccessibility of target sites for nisin. Disruption of the outer membrane permeability barrier by several methods including chelation of cations by ethylenediaminetetraacetic acid (EDTA) and various physical stresses including osmotic shock, heat shock, acid and freezing, have been shown to sensitize Gram-negative cells to nisin. We discovered that nisin enhanced inactivation of S. typhimurium and E. coli O157:H7 when stored at 6.5 degree C in peptone water. Cell numbers, enumerated on trypticase soy agar (TSA) decreased over 2 weeks in the presence of nisin more rapidly than in the absence of nisin. Salmonella typhimurium exhibited a 1.7 log decrease in cell numbers (average of 17 trials), in the presence of 100IU nisin compared to controls (P<0.0001). Likewise, four strains of E. coli , including O157:H7, also showed a significant (P<0.001) 1.6 log decrease in cell numbers after 7 days in the presence of nisin at 6.5 degree C. This effect of nisin was completely reversed by the presence of 25 mM magnesium or 100 mM sodium or potassium. Nisin may be a means for providing an additional barrier to enhance the safety of refrigerated foods.