title: Fast induction of nisin resistance in Streptococcus thermophilus INIA 463 during growth in milk.
abstract: Streptococcus thermophilus INIA 463 became nisin-resistant after exposure in skim milk to subminimal inhibitory concentrations of nisin (1-3 IU/ml) for less than 2 h. Addition of 20 IU/ml caused a 4 log unit decrease in S. thermophilus counts of a culture not exposed previously to nisin, whereas no decrease was observed in the culture exposed to nisin for 2 h. Transfer of immunity genes as responsible for nisin resistance was discarded. The presence of extracellular or intracellular specific nisin-degrading enzymes was not detected in the nisin-resistant variant of S. thermophilus INIA 463. Nisin resistance was caused by the induction of a resistance mechanism. Transmission electron microscopy (TEM) revealed that the nisin-resistant variant of S. thermophilus INIA 463 had a thickened cell wall compared to the wild strain. Resistance to nisin was lost after one transfer (4 h growth) in nisin-free skim milk.
authors.affiliation: Departamento de Tecnología de Alimentos, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Carretera de La Coruña Km 7, Madrid 28040, Spain.
authors.forename: Sonia
authors.initials: S
authors.lastname: Garde
authors.forename: Marta
authors.initials: M
authors.lastname: Avila
authors.forename: Margarita
authors.initials: M
authors.lastname: Medina
authors.forename: Manuel
authors.initials: M
authors.lastname: Nuñez
mesh_terms: D000818:Animals; D002473:Cell Wall / Q000187:drug effects / Q000648:ultrastructure; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008892:Milk / Q000382:microbiology*; D009561:Nisin / Q000494:pharmacology*; D048249:Streptococcus thermophilus / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure
chemical_list: D009561:Nisin