Three methods for molecular typing of methicillin-resistant Staphylococcus aureus using polymerase chain reaction (PCR) were compared. The method which amplified the variable number of tandem repeat ofdru sequences grouped the isolates into six types. Whereas, the method examining restriction fragment length polymorphism of coagulase gene and the method using arbitrarily primed-PCR showed poor diversity in typing. We investigated the distribution of dru types in two hospitals. Obvious concentration of a type in one ward was not recognized in our hospital. In the other hospital, a rare type was detected from the inpatients in the pediatrics ward. It suggested that the infection was an epidemic. Wealso found that some patients were infected with more than two strains. Even if two isolates show the same type, it does not necessarily mean that they originated from one clone. However,this method brings meaningful information on nosocomial infection, more easily than other genotyping. (Internal Medicine 36: 694-699, 1997)

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