Identification

The emerging clinical importance of staphylococcal infections prompted us to establish a reference database for partial RNA polymerase B (rpoB; nucleotides 1444– 1928) gene sequences from type strains of all staphylococ-cal species and subspecies. This database correctly identi-fied 55 clinical staphylococcal isolates; all were correctly identified at the species level. At the subspecies level, rpoB misidentified only 2 isolates. The emerging clinical importance of Staphylococcusaureus and coagulase-negative staphylococci (1) in connection with the expanding number of staphylococcal subspecies described requires accurate identification to the subspecies level. Currently, the genus Staphylococcus is divided into 36 species and 21 subspecies. Staphylococcal subspecies not included in the databases of commercial identification systems, as well as phenotypic variants (e.g., small-colony variants), are often misidentified (2). We recently described the usefulness of genotypic iden-tification of staphylococcal subspecies by using partial 16S rDNA sequences in comparison with phenotypic tests (3). However, the partial 16S rDNA sequences used were not discriminative enough to differentiate all staphylococ-cal subspecies. When searching for a molecular target for discrimination of staphylococci, several genes have been evaluated, e.g., heat shock protein 60 (hsp60) (4), superox-ide dismutase A (sodA) (5), and RNA polymerase B (rpoB) (6). However, these studies concentrated only on a limited number of staphylococcal species. Therefore, a complete reference database of partial rpoB gene sequences from type strains (n = 47) and other culture collection strains, including all validly described staphylococcal subspecies, was created for this study. This reference database was then evaluated with clinical isolates. Results were com-pared with those previously obtained by 16S rDNA sequencing and conventional phenotypic tests. The Study We analyzed 82 type and other culture collection strains encompassing all validly described staphylococcal species (n = 38) and subspecies (n = 21; according to the curren