Discrimination of

B. cereus B. anthracis B. cereus B. anthracis B. cereus B. anthracisB. cereus B. cereus The present invention relates to methods and compositions for using nucleotide sequence variations of 16S and 23S rRNA within the group to discriminate a highly infectious bacterium from closely related microorganisms. Sequence variations in the 16S and 23S rRNA of the subgroup including are utilized to construct an array that can detect these sequence variations through selective hybridizations and discriminate group that includes . Discrimination of single base differences in rRNA was achieved with a microchip during analysis of group isolates from both single and in mixed samples, as well as identification of polymorphic sites. Successful use of a microchip to determine the appropriate subgroup classification using eight reference microorganisms from the group as a study set, was demonstrated.