Resistance to nisin and production of nisin-inactivating enzymes by several Bacillus species.

The resistance to nisin was examined for the vegetative forms and the endospores of 14 strains of 9 species of the genus Bacillus. Bacilli, endospores and culture filtrates were tested for ability to inactivate nisin. Marked antinisin activity was detected in extracts of bacilli and endospores of organisms which have a lytic mechanism for rupture of the spore coat (type L); little or no activity was observed in extracts from organisms which rupture the spore coat mechanically (type M). No significant extracellular activity was detected, except after the autolysis of bacilli. When organisms were cultivated in the presence of nisin (50 Reading units/ml. ; Berridge, 1949) the yield of organisms and the specific activity of the extracts was decreased; evidence to explain these observations is presented. No quantitative correlation was observed between the production of anti-nisin activity and the resistance of vegetative forms. The anti-nisin activity of cell-free extracts of bacilli of two species (Bacillus cereus and B. polymyxa) was studied further; there was evidence that the activity was probably enzymic. A preliminary study of the properties of the enzymes from these organisms was made. It was found that the anti-nisin enzymes of two strains of B. cereus differed from the lytic enzymes previously described (Strange & Dark, 1957a, b). The anti-nisin enzymes had no effect on polymyxin, gramicidin or bactracin but inactivated subtilin. Proteolytic activity was not observed in the preparations.