title: Consequences of the development of nisin-resistant Listeria monocytogenes in fermented dairy products.
abstract: Wild Listeria isolates representing serovars found in artisanal cheeses commercialized in Asturias (northern Spain) were assessed for their susceptibility to several bacteriocins. Pediocin PA-1 was the most active bacteriocin followed by enterocin AS-48, nisin, and plantaricin C. However, some Listeria monocytogenes and Listeria innocua strains were already highly resistant to PA-1. Among the wild L. monocytogenes populations, the frequency of development of nisin resistance ranged from 10(-6) up to 10(-3), depending on the strain. Highly stable mutants with increased nisin resistance (two- to fourfold) were isolated and tested for potential cross-resistance to lysozyme, EDTA, and various NaCl concentrations and pH values. All mutants were cross-resistant to lysozyme but sensitive to EDTA. In contrast, no clear correlation could be established between nisin resistance and an altered susceptibility to NaCl or pH changes. Nisin-resistant variants were able to survive and even to multiply in milk fermented by a nisin-producing Lactococcus, but the growth of the wild-type strain was inhibited. The different phenotypes evaluated in this study are indicative of the unpredictability of the consequences of the development of nisin resistance in a dairy environment. This resistance should be considered when making a risk assessment of the long-term use of nisin to control L. monocytogenes.
authors.affiliation: Instituto de Productos Lácteos de Asturias, Consejo Superior de Investigaciones Cientificas, 33300 Villaviciosa, Asturias, Spain. bmf1@ipla.csic.es
authors.forename: Beatriz
authors.initials: B
authors.lastname: Martínez
authors.forename: Diego
authors.initials: D
authors.lastname: Bravo
authors.forename: Ana
authors.initials: A
authors.lastname: Rodríguez
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001430:Bacteriocins / Q000494:pharmacology; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D043302:Cultured Milk Products / Q000382:microbiology*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development*; D008826:Microbial Sensitivity Tests; D009113:Muramidase / Q000494:pharmacology; D009154:Mutation; D009561:Nisin / Q000494:pharmacology*; D000070017:Pediocins; D018570:Risk Assessment; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001430:Bacteriocins; D000070017:Pediocins; C074288:pediocin PA-1; D009561:Nisin; D012965:Sodium Chloride; D009113:Muramidase