Occurrence of Bacillus cereus and Bacillus licheniformis strains in the course of UHT milk production Výskyt kmenů Bacillus cereus a Bacillus licheniformis v procesu výroby UHT mléka

Transfer of Bacillus cereus and Bacillus licheniformis strains from milk into final products (UHT milk) was studied. Phase milk samples were collected during the whole time of milk processing (one milk batch) in collaboration with the dairy. Representative B. cereus and B. licheniformis strains were characterised and compared by ribotyping with EcoRI enzyme and a probe complementary to Escherichia coli 16S and 23S rRNA as well as by phenotyping. According to 26 phenotypical traits the B. licheniformis strains formed almost a homogeneous group. In contrast, B. cereus strains exhibited variable results in several tests. The hybridisation profiles divided the analysed strains into two groups in full accordance with their species classification. Band patterns of B. cereus strains showed similarities ranging from 77 to 97%; this similar- ity values correlated with biochemical test results as well. B. licheniformis strains exhibited band pattern similarities from 82 to 100%. The hybridisation profiles of B. licheniformis strains B79 (pasteurized milk) were absolutely identical (100% similarity). Their phenotypical test results were identical as well. These results imply the identity of the strains isolated in the course of UHT milk production.

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