No abstract

We compared the results of two typing methods for 678 strains of methicillin-resistant Staphylococcus aureus and methicillin-susceptible S. aureus. PCR-restriction fragment length polymorphism typing of the coagulase gene was a more reliable method than coagulase serotyping from the viewpoint of arbekacin resistance.

A total of 472 clinical strains of methicillinresistant Staphylococcus aureus (MRSA) isolated in Japan between 1979 and 2000 were investigated for resistance to 8 aminoglycosides, 4 aminoglycoside-modifying enzyme gene profiles, and AluI-restriction fragment length polymorphism of the coagulase gene determined by polymerase chain reaction assay. The majority of MRSA strains tested belonged to 4 groups based on coa-RFLP: L21, L22, L31, and M22. About 90% of recent isolates belonged to type L21, indicating the spread of a specific type of MRSA in Japan. Of the type L21 strains, 41.9% included the aac(6Ј)/aph(2Љ) gene, which was one of the risk factors of arbekacin (ABK) resistance, but only 5.5% were resistant to ABK. In contrast, all of the type M22 strains carried aac(6Ј)/aph(2Љ) and 70.1% showed ABK resistance. Among the other types, less than 20% of strains showed ABK resistance. These results suggested that ABK has maintained potent activity. If the predominance of type L21 continues, there will be no progression to ABK resistance in MRSA. However, it may be necessary to monitor the trends in type M22 continuously.

Using colony direct PCR we established, kan gene (GenBank accession No. AB028210) coding for an aminoglycoside acetyltransferase, AAC(3), was surveyed among strains of Streptomyces griseus and its related taxa (S. anulatus group). The regulatory and ORF regions of kan gene were targeted by the use of original primers. With the regulatory region primers, the target fragment (518 bp) amplification was observed in all the streptomycin (SM)-producing strains of S. griseus and in several strains of S. anulatus group. The other target fragment (930 bp) amplification using the ORF primers was observed only in the SM-producing strains of S. griseus including 'S. ornatus' that has substantially identical properties to those of S. griseus. It was thus conclusive that kan gene is highly conserved in SM-producing strains of S. griseus and distributed in taxa related to S. griseus. There were numbers of strains that provided no amplification upon PCR but hybridization bands upon Southern hybridization, suggesting the lack or alteration of kan gene. Characterization by colony direct PCR using appropriate primers will be a big help for taxonomic as well as ecological characterization of actinomycetes.