水産食品の腐敗中毒に関する研究-VIII

Abstract

A strain of Proteus morganii, presumably the causative organism of an outbreak of allergy-like food poisoning from eating raw flesh of big-eyed tuna (Parathunnus mebachii) was isolated by the authors in 1955. The organism was characterized by the production of a large amount of histamine and other unknown vagus-stimulant named “saurine”. The present paper deals with the distribution of l-histidine decarboxylase among Proteus group as tested with washed cell suspension and the response of the decarboxylating activity upon varying pHs. In addition, the stability of the enzyme in washed cell suspension against temperature and the ability to form ammonia from l-histidine or mackerel infusion medium were studied. Results obtained may be summarized as follows: 1. The presence of l-histidine decarboxylase in washed cell suspensions of 13 strains of Proteus morganii was confirmed, however, the rate of production of histamine was markedly different depending upon strains. Whereas, a very slight activity of l-histidine decarboxylase was detected in strains of P. mirabilis, P. rettgeri or P. vulgaris tested. 2. The l-histidine decarboxylation by washed cell suspension of any of Protea tested, reacted at a range of pH value between 5 and 8 and the activity was the highest at pH 6.0 to 6.5. 3. It is noteworthy that a marked difference was observed in the specificity between l-histidine decarboxylase of P. morganii and that of Cl. perfringens, viz., the former decarboxylates l-histidine at such a wide reaction range as pH 4 to 8, in which the pH of optimum activity was at 5.8, while the activity of the latter limited in an acid side below pH 5.5 and the optimum pH was 3.2. 4. The l-histidine decarboxylase in washed cell suspension of P. morganii was found to be fairy stable at a temperature between 4° to 24°C for 96 hours. While, at 37°C, about 95 per cent of enzyme was inactivated in 24 hours and no detectable activity remained after 96 hours. On the other hand, keeping the suspension in a freezer at -20°C destructed about 70 per cent of activity in 24 hours, however no further inactivation was observed for 96 hours. 5. No appreciable amount of ammonia was formed when certain strains of P. morganii were grown in the mackerel infusion media at 25°C for 48 hours, or when a washed cell suspension was mixed with l-histidine in buffer solutions at pH 4.5 to 9.0 and incubated at 37°C for 3 hours. 6. The facts described above may suggest that the l-histidine decarboxylase of P. morganii is quite different in nature from that of Cl. perfringens.