乳酸球菌および酪酸菌に対するナイシンの抗菌効果

抄録

　This study was designed to determine the basic characteristics of nisin-producing lactic acid bacteria. The optimal conditions of culture of this bacteria and the antibacterial effect of nisin on LD type starter bacteria, and on butyric acid bacteria which induces gas blowing during cheese ripening, was determined.
　The optimal temperature for growth of nisin-producing lactic acid bacteria was between 20 and 25℃, while that for acid production was between 30 and 35℃. High temperature was suitable for nisin production, and about 300 IU/ml of nisin was produced during cultivation of nisin-producing lactic acid bacteria in skim milk at 30℃ for 24 hrs.
　Mixed culture of LD typel actic starter and nisin-producing lactic acid bacteria inhibited the acid production of LD type starter. This inhibition was frequently observed in the early phase of cultivation, and was caused by nisin transferred from precultures of the nisin-producing lactic acid bacteria at inoculation. Thus, various extents of inhibition were observed for different sorts of precultures of the nisin-producing lactic acid bacteria and for different sizes of inoculum.
　In the LD type starter, Lactococcus lactis subsp. cremoris SC-1 and SC-3 exhibited the highest sensitivity to nisin; its growth was inhibited with about 2 IU/ml of nisin. However, this strain became resistant to extremely high concentrations of nisin when nisin content gradually increased during cultivation. The growths of L. lactis subsp. lactis biovar. diacetylactis SD-1 and SD-3, and Leuconostoc mesenteroides subsp. cremoris LC-2 were inhibited at about 5 and 20 IU/ml of nisin, respectively, while L. lactis subsp. lactis SL-2 could grow at between 50 and 100 IU/ml of nisin, and thus exhibited significant resistance to nisin. On the other hand, of the clostridia, which displayed variation in sensitivity to nisin depending on the number of inoculated spores, Clostridium tyrobutyricum KS-222 exhibited the highest sensitivity, with growth inhibition at about 20 IU/ml of nisin in the presence of 1×10² spores/ml. The growth of Cl. butyricum K-53 was inhibited at about 50 IU/ml of nisin, while Cl. sporogenes K-21 could grow even at 100 IU/ml.
　The concentration of nisin decreased during cultivation of L. lactis subsp. lactis SL-2, Cl. butyricum K-53 and Cl. sporogenes K-21, which displayed resistance to nisin, suggesting that these strains were able to inactivate nisin.