Vital States of Sh. sonnei and S. typhi in Water and Various Kinds of Food

Abstract

In order to obtain the basic data to prevent the outbreaks of Shigellosis and Typhoid fever caused by polluted drinking water or foods, the fate of Sh. sonnei and S. typhi in well water and various kinds of food were investigated.Both Sh. sonnei and S. typhi, which can be survived for at least 6 days or longer in well water, were killed within 6 hours by adding 0.4ppm of chlorine. When well water polluted with stool was disinfected with the same amount of chlorine, the both bacteria survived 18-96 hours. The polluted well water in this expemiments was prepared by adding stool in such an amount (0.001%), as to give no perceptible change in tint, turbidity and smell. Further detailed experiments revealed that in successful chlorine disinfection to both bacteria in the above mentioned polluted well water or standing water, such an amount of sodium hypochlorite as to produce 3ppm/ml of free chlorine is necessary.Experiments on food were performed with bread, salad, “Fukujinzuke” (a kind of Japanese pickles), raw cream, commercial milk and cheese, all of which can be taken without any treatment, and beefs untreated and heated at 100°C for 30 minutes. In this experiments, bread and “Fukujinzuke” were preserved at 25°C, and other foods were preserved at 5°C. All of these were inoculated with each 106 cells of Sh. sonnei and S. typhi, respectively, and the fate of these bacteria were pursued.In bread, both bocteria survived as long as 30 days. In salad, they showed slight growth at 4 hours after the inoculation, and remained constant level for the succeeding 20 days, after that the curves weme declined gradually, and in the case of S. typhi, they diminished at the 30th day, but in the case of Sh. sonnei, they could survive little longer. In case of raw cream, both of the bacteria were demonstrated until the end of the 4th week, and in commercial milk, S. typhi survived for 30 days and Sh. sonnei more than 75 days. In raw beef, they survived more than 10 days. In heat treated beef, Sh. sonnei survived for 2 weeks, and S. typhi for 4 weeks. In case of “Fukujinzuke”, the results were quite different from other above mentioned foods, i. e., both bacteria were killed within 48 hours after inoculation. This is considered to be the influence of food preservatives contained in this pickle.