Variation in rRNA operon number as revealed by ribotyping of Bacillus anthracis strains

Ribotyping of various Bacillus strains with one restriction enzyme (AccI) revealed significant similarity between Bacillus anthracis strains, Bacillus thuringiensis and Bacillus cereus strains, which are all members of the Bacillus cereus group. A further ribotyping study of 10 virulent and 8 attenuated B. anthracis strains, using 4 endonucleases and both 23S and 16S probes independently, was performed. The discrimination index D of Hunter and Gaston showed that the best combination for future large-scale ribotyping studies would be either the combination of AccI and 23S, or that of EcoRI and 16S. Depending on the B. anthracis strain analyzed 10 or 11 rRNA operons were found. In all cases, many strains were grouped into 2 to 3 patterns. Attenuated strains, including a laboratory-cured strain, yielded aberrant patterns.