Molecular typing of Staphylococcus aureus on the basis of coagulase gene polymorphisms

Staphylocoagulase, a major phenotypic determinant of Staphylococcus aureus, exists in multiple allelic forms, in part because of the existence of gene variants within the 3'-end coding region. This region contains a series of repeating 81-bp DNA sequences which differ both in the number of tandem repeats and the location of AluI restriction sites among different isolates. Utilizing this finding, we developed a novel typing method for S. aureus based on polymerase chain reaction amplification of the variable region of the coagulase gene followed by AluI restriction enzyme digestion and analysis of restriction fragment length polymorphism (RFLP). Among 30 S. aureus isolates studied initially, a total of 10 distinct RFLP patterns were observed. There was excellent correlation of the RFLP patterns with typing of these isolates by multilocus enzyme electrophoresis at 20 chromosomal loci. This coagulase RFLP method was used to analyze an additional 39 S. aureus isolates and successfully traced the source of an outbreak of methicillin-resistant S. aureus infections at a local hospital.