Identification of aminoglycoside-modifying enzymes by susceptibility testing: epidemiology of methicillin-resistant Staphylococcus aureus in Japan.
A multiple-primer PCR was used to identify genes encoding aminoglycoside-modifying enzymes in 381 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). The technique used three sets of primers delineating specific DNA fragments of the aph(3')-III, ant(4')-I, and aac(6')-aph(2") genes, which influence the MICs of gentamicin, tobramycin, and lividomycin. Isolates with none of the three genes detected were susceptible to all three agents. Isolates with the aph(3')-III gene showed resistance to lividomycin (MIC > 1,024 microg/ml), and those with the ant(4')-I gene were resistant to tobramycin (MIC > or = 8 microg/ml). Isolates with only the aac(6')-aph(2") gene were resistant to gentamicin (MIC > or = 8 microg/ml) and tobramycin in decreasing order; those with both the ant(4')-I and aac(6')-aph(2") genes also were resistant to gentamicin and tobramycin, but in increasing order. Susceptibility testing, then, could detect specific genes. In 381 Japanese MRSA isolates, the ant(4')-I, aac(6')-aph(2"), and aph(3')-III genes were prevalent in 84.5, 61.7, and 8.9%, respectively. Isolates with only the ant(4')-I gene had coagulase type II or III, but isolates with both the ant(4')-I and aac(6')-aph(2") genes included all coagulase types. Most isolates with coagulase type IV or VII carried the aac(6')-aph(2") gene. Of the MRSA isolates with ant(4')-I and/or aac(6')-aph(2") genes, 97% were resistant to aminoglycosides in clinical use, but a new aminoglycoside, arbekacin, had excellent activity against these isolates.
Ida
T
T
Department of Microbiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan.
Okamoto
R
R
Shimauchi
C
C
Okubo
T
T
Kuga
A
A
Inoue
M
M
D000123:Acetyltransferases / Q000235:genetics; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology*; D003030:Coagulase / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D006801:Humans; D007564:Japan / Q000453:epidemiology; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D009713:Nucleotidyltransferases / Q000235:genetics; D010770:Phosphotransferases / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D003030:Coagulase; D000123:Acetyltransferases; D010770:Phosphotransferases; D009713:Nucleotidyltransferases