Emergence of quinolone resistance among clinical isolates of methicillin-resistant Staphylococcus aureus in Ontario, Canada.
One hundred two isolates of methicillin-resistant Staphylococcus aureus (MRSA) randomly selected from across the Canadian province of Ontario were tested for their susceptibility to ciprofloxacin, norfloxacin, and nalidixic acid by the agar dilution method. Forty-nine percent (50 of 102) had high levels of resistance to these quinolone compounds. For the 50 resistant isolates, ciprofloxacin and norfloxacin had high MICs for 90% of isolates (MIC90s) of 128 micrograms/ml and greater than 128 microgram/ml, respectively; for these isolates, the nalidixic acid MIC90 was greater than 640 micrograms/ml. The majority (98%) of the 50 isolates were also resistant to tobramycin (MIC90, greater than 128 micrograms/ml), while 42% of the isolates were resistant to gentamicin (MIC90, 64 micrograms/ml). Quinolone-resistant MRSA isolates were susceptible to bacteriophages from several groups, indicating independent selection of resistant strains. These results suggest that a reappraisal of the use of fluoroquinolones against MRSA in Canada is necessary.
Harnett
N
N
Clinical Bacteriology Section, Central Public Health Laboratory, Toronto, Ontario, Canada.
Brown
S
S
Krishnan
C
C
D042462:4-Quinolones; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002170:Canada; D004352:Drug Resistance, Microbial; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D013211:Staphylococcus aureus / Q000187:drug effects*
D042462:4-Quinolones; D000890:Anti-Infective Agents