The effect of nisin on the physiology of Bifidobacterium thermophilum

The effects of nisin on lactate accumulation, growth, and Fe(III) binding by Bifidobacterium thermophilum (ATCC 25866) and Bifidobacterium breve (ATCC 15700) were investigated. Nisin inhibited lactate production by B. thermophilum at concentrations of less than 1 microg/ml, but this effect could be largely eliminated by pretreatment of the organism with 100 to 400 microM Al(III) or La(III). Nisin also inhibited the growth of B. thermophilum at concentrations of 2 to 3 microg/ml, with lower concentrations showing lag periods and/or slower rates of growth. However, Al(III) could not negate these effects, most likely because of Al(III) chelation by the trypticase-proteose-yeast extract medium. Nisin was able to increase instantaneous Fe(III) binding by both B. thermophilum and B. breve, though prolonged-time experiments (up to 120 min) with B. thermophilum indicated no difference in total Fe(III) bound. Nisin was thus able to increase the free radical reaction rate with bifidobacteria and the resultant rate of Fe(III) binding. It was concluded that nisin will normally inhibit the metabolic activity of B. thermophilum along with that of certain bacterial pathogens; however, this effect may in some instances, be abated by a pretreatment with Al(III). Moreover, by accelerating free radical action and the binding of iron by bifidobacteria, nisin may be able to potentiate their normal probiotic action.