Identification of Bacillus strains isolated from milk and cream with classical and nucleic acid hybridization methods.

A total of 529 bacterial strains have been isolated from milk and cream sampled at different sites in a dairy production plant under conditions selective for aerobic sporeforming bacteria. Identification with classical methods based on morphological, physiological and biochemical criteria showed Bacillus licheniformis to be the most frequently occurring Bacillus sp. The investigation also revealed 62 unidentified strains. Classical identification methods were time consuming (3-7 d), lacked specificity and--because of their dependence on phenotypic gene expression--sometimes produced ambiguous results. Consequently, a colony hybridization method developed for the identification of B. licheniformis strains and using nonradioactive labelled 23S rRNA targeted oligonucleotide probes was also used. Identification of B. licheniformis with both classical and hybridization methods revealed diverging identification results for 70 strains.