| Popis: |
In June 1974 a serious outbreak salmonellosis was reported from the southeast of Sweden. The epidemic was caused by Salmonella typhimurium and spread by infected cream, packed in one-way paper-plastic containers. Ordinary pasteurization of cream purposely infected with the strain in question at 60 degrees for 38 sec or 67 degrees C for 4,5 sec, resulted in a reduction by more than 7 decimal logs (Table I). The decimal reduction time at 60 degrees in cream was estimated to roughly 1.3 sec. The cream, which caused the outbreak, was pasteurized at 90 degrees C for 2-3 sec, which should destroy all salmonella in raw cream. In Sweden pasteurized cream has to be stored at a temperature not higher than 8 degrees C. The isolated salmonella strain was not able to grow at + 8 degrees or at + 10 degrees C during 17 days in pasteurized or UHT-treated cream. During this storage the viable counts were reduced by 79% at 8 degrees and 54% at 10 degrees C. Minimum growth temperature of the strain was 11-12 degrees C. The mean generation time in pasteurized cream at 12 degrees was 9.4 hours and at 15 degrees C 3.4 hours (Fig. 1 and 2). The salmonella strain was able to grow in competition with other bacteria in pasteurized cream even at low levels of infection (Table II). An exposure to a higher temperature, followed by storage at + 8 degrees C did not cause a further growth of salmonella at the low temperature (Fig 3). To avoid a recurrence, the possibility of reinfection of the cream with salmonella has to be further decreased and the cream has to be stored at a low temperature during all the storage period. |
