Usefulness of Bacteriological Tests and sspE PCR for Identification of Bacillus cereus Group

ABSTRACT

The Bacillus cereus group includes B. anthracis, B. cereus, B. thuringiensis, B. mycoides, B. weihenstephanensis, B. pseudomycoides. The members of B. cereus group shares strong degree of DNA sequence similarity. Even though the biochemical test and bacteriological test have been used to identify the B. cereus group, an accurate identification system of the B. cereus group is required. We have developed a highly specific PCR-based assay for the B. cereus group chromosome using a sequence motif found within a spore structural gene (sspE). Using the assay, we were able to discriminate B. anthracis from the other members of B. cereus group. We also tried to find a new system for the B. cereus group identification. Five bacteriological tests (hemolysis, motility, penicillin susceptibility, rhizoid growth, toxic crystal formation), API system (API 50CHB & API 20E), MLST and sspE PCR were performed on 28 strains of the B. cereus group. The dendrogram generated from API system and bacteriological tests revealed that B. cereus and B. thuringiensis are grouped into the same cluster. In combination of sspE PCR and bacteriological tests, the dendrogram showed that 4 strains of B. cereus clustered within the same group. B. thuringiensis formed the subgroup in the same cluster. All strains of B. mycoides were encompassed together. Another cluster only included B. anthracis. The best system was determined to be sspE PCR and bacteriological tests. It is concluded that sspE PCR and bacteriological tests could be used for rapid discrimination and identification of B. anthracis and provided an effective means of differentiation between the B. cereus group.