Mode of Action of Nisin on some Representative Bacterial Spores

Abstract

Summary The mode of action of nisin on the most dominant aerobic and anaerobic spore-formers, isolated from milk and processed cheese, together with some known strains was studied. The effect of nisin on 12 times washed spores of aerobic spore-formers, representing the three groups put forward by Smith, Gordon, and Clark (1952). From group I, two strains of B. subtilis, B. megatherium, B. licheniformis , and B. coagulans . From group II B. stearathermophilus and B. polymyxa . From group III B. sphaericus . Anaerobic spore-formers, namely Cl. welchii and Cl. sporogenes , were studied in phosphate buffer M/100 at p H 6.4. It was generally found that nisin exerted neither sporocidal effect nor any germination induction on spores of the afore-mentioned species. This, in fact, came to after several trials in which high dilution factor was used to eliminate the carry over of nisin in the recovery media. When low dilution factor was used, anomalous results were obtained. The use of high dilution factor dispute the conception that nisin is firmly bound to the spores, but it can be stated that it only remained in the surrounding medium, hence lost through dilutions, thus count restored to normal. The concept of carry-over of nisin to the recovery media when the low dilution factor was used, giving anomalous results and thus inducing several investigators to state a sprocidal effect, was fully confirmed. This was established by the inactivation of nisin in the origin or in the recovery media by proteolytic enzymes (trypsin and pancreatin) or by adjusting the p H to alkalinity (phosphate buffer at p H 8). Both treatments restored the count to normal, i.e., being in the same order as the initial, indicating that nisin has sporostatic but no sporocidal effect.