Identification of Bacillus strains as contaminants in soybean milk by rapd (random amplified polymorphic DNA) analysis and southern blotting with 23S rRNA-targeted oligonucleotide probes (Ribotyping)

摘要

Even if a sporeformer is subjected to heat processing, in some cases it can survive in food. We focused on Bacillus, a sporeformer. We gathered 22 kinds of marketed soybeans, mixed them in equal amounts, heated them at 90°C for 5 min and made soybean milk for experiments in our laboratory. We isolated Bacillus cereus and Bacillus licheniformis from the milk and tried to identify the source of contamination. These bacteria were also isolated from 22 kinds of soybeans. Total DNA were extracted fromthe isolates and compared by RAPD analysis (Random Amplified Polymorphic DNA) and Southern blotting with 23S rRNA-targeted Oligonucleotide probes, and RiboPrinter(R) (Qualicon). It was supposed that the B. licheniformis isolated from the product was identical to the B. licheniformis from one of the raw materials. Moreover, as the B. cereus of the product differed from the B. cereus present in the original soybeans at the genomic level, it appeared that the contaminants were derived from our laboratory environment. For B. licheniformis and B. cereus, we constructed a primer that was effective in RAPD analysis. The Ribotyping reported in this paper might be effective for the polymorphic analysis of B. cereus.