Multiplex PCRs for assignment of Staphylocoagulase types and subtypes of type VI Staphylocoagulase

Staphylocoagulases (SCs) have been classified by the differences in antigenicity using a serological method. We have developed a system to classify them based on the nucleotide differences in SC genes (coa). The system was composed of three multiplex PCRs (M-PCRs): M-PCR:A, identifying types III, IV, VII, and VIII; M-PCR:B, identifying types I, II, V, and VI; M-PCR:C, identifying three subtypes of type VI. In this study, we found that coa genes of the serotype VI were not identical, but classified into three subtypes based on the nucleotide differences, especially in D2 and the central region: VIa, the coa gene carried by stp12 from human; and VIb and VIc, the coa genes carried by strains IFH556 and IFH514 isolated from bovine raw milk. The primer pair used in M-PCR:B was designed to identify all three subtypes of type VI coa. The results showed that coa types of 154 out of 155 Staphylococcus aureus strains from various origins assigned by M-PCR:A and B were identical to those obtained by serological methods, leaving a serotype IV strain unclassifiable. All 73 type VI strains were classified into one of three subtypes by M-PCR:C. Furthermore, we found that type VIa and VIb strains carried characteristic pyrogenic toxin superantigen genes, while no toxin genes were identified in type VIc strains, suggesting the correlation between the subtype of type VI coa gene and the carriage of genomic islands. Our results showed that these M-PCRs are convenient methods for SC typing that might be useful for epidemiological studies.