Misao Haruta

Studies on the Heat-resistability of Coliform Organisms in Milk, Especially the Dormancy of the Heat Shocked Organisms

In the series of our researches into the heat resistability of coliform bacteria in milk we recognized that the heat-shocked bacteria showed the phenomenon of dormancy in its culture medium.After milk in which the strain of E. Coli I type was suspended was heated at 61°, 62° and 63°C respectively, the survived bacteria in the milk was tested at definite time intervals. As the results of our experiments, we could find that the development by the heated bacteria of its colonies was rather belated and moreover the longer it was heated the more remarkable the tendancy was, although the non-heated bacteria completely developed its colonies on the desoxycholate agar in 20-24hrs. and on the Endo agar in 48hrs.Judging from the above mentioned, we must once take it into consideration that the heated bacteria has the period of dormancy during its cultivation, when we bacteriologically test the pasteurization effect of bottled milk and the suitability of its treatment process immediately after finishing the sterilizati on, or when we make close nquiries into the origin of coliform bacteria detected in bottled milk in accordance with the present method for testing coliform bacteria.