MODEL INVESTIGATIONS INTO THE PSYCHROTROP HIC GROWTH OF YERSINIA-ENTEROCOLITICA

Cold storage cannot permanently inhibit an undesirable growth of micro -organisms in food. Psychrotrophic bacteria and fungi are of special i nterest in this context. Previous information concerning the ability o f Yeusinia (Y.) enterocolitica (e.) to grow at temperatures at or belo w 0 degrees C are insufficient. Therefore, adequate model investigatio ns at temperatures from -1 to -5 degrees C were undertaken, using near ly 90 Y. strains of different origin. The plate-count dynamic in nutri ent broth was studied for a period of 3 weeks. In order to characteriz e the dynamic of bacterial growth, the quotient (Q) between the Y. pla te counts at both the end and beginning of the investigation was calcu lated. 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 th e examination, the percentage of strains with at least doubled initial plate count was, at -1 degrees C, about 85 %, about 85 % at -2 degree s 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.