[Model studies of psychrotrophia in Yersinia enterocolitica]

Cold storage cannot permanently inhibit an undesirable growth of micro-organisms in food. Psychotrophic bacteria and fungi are of special interest in this context. Previous information concerning the ability of Yersinia (Y.) enterocolitica (e.) to grow at temperatures at or below 0 degrees C are insufficient. Therefore, adequate model investigations at temperatures from -1 to -5 degrees C were undertaken, using nearly 90 Y. strains of different origin. The plate-count dynamic in nutrient broth was studied for a period of 3 weeks. In order to characterize the dynamic of bacterial growth, the quotient (Q) between the Y. plate counts at both the end and beginning of the investigation was calculated. Each increase of the plate count to at least double the initial population was regarded as growth in the true sense. At the end of the examination, the percentage of strains with at least doubled initial plate count was, at -1 degrees C, about 85%, about 85% at -2 degrees C, 59% at -3 degrees C, nearly 16% at -4 degrees C, and about 13% at -5 degrees C. These results make it clear that there are numerous Y.e. strains that are able to grow at temperatures below 0 degrees C. Moreover, several strains can even grow at -5 degrees C.