Nisin resistance in Clostridium botulinum spores and vegetative cells

The frequencies at which vegetative cells and spores of Clostridium botulinum strains 56A, 62A, 17409A 25763A, 213B, B-aphis, and 169B formed colonies on agar media containing 0, 10(2), 10(3), and 10(4) IU of nisin per mi at 30 degrees C were determined. Strain 56A had the highest frequencies of nisin resistance, while strains 62A, 169B, and B-aphis had the lowest, For most strains, spores were more resistant than vegetative cells. One exposure to nisin was sufficient to generate stable nisin-resistant isolates in some strains, Stepwise exposure to increasing concentrations of nisin generated stable resistant isolates from all strains, Spores produced from nisin-resistant isolates maintained their nisin resistance, The frequency of spontaneous nisin resistance was reduced considerably by lowering the pH of the media and adding 3% NaCl. Nisin-resistant isolates of strains 56A and 169B also had increased resistance to pediocin PA1, bavaricin MN, plantaricin BN, and leuconocin S.