CHARACTERIZATION OF NISIN-RESISTANT VARIANTS OF PEDIOCOCCUS-ACIDILACTICI UL5, A PRODUCER OF PEDIOCIN

Four spontaneous nisin-resistant variants R1, R1M, T5 and T7 of Pedioc occus acidilactici UL5, a pediocin producer, were isolated on a nisin gradient. The minimum inhibitory concentration of Fed acidilactici UL5 using an agar diffusion test was 0.25 ng, while that of R1, R1M, T5 a nd T7 were 10, 25 and more than 32.5 mu g for the two latter, respecti vely. Nisin resistance phenotype was stable after 60 generations in MR S nisin-free liquid media and 10 consecutive transfers in solid medium . Pediococcus acidilactici UL5 and its nisin-resistant variants exhibi ted the same total DNA profile, level of production of pediocin and ad sorption of nisin on the cell surface. The specific growth rate (mu) d ecreased with the level of resistance of the culture. Nisin-resistant Variants and parental strain UL5 showed differences in sensitivity to antibiotics in which some act on the cell surfaces. Moreover, the fatt y acid composition of the cell wall in nisin-resistant variants, compa red with UL5, was different, particularly in C16:1 and C18:1. Results suggest that a change in structure/composition of nisin-resistant vari ants might be associated with nisin resistance.