Development of new antibiotic resistance in methicillin-resistant but not methicillin-susceptible Staphylococcus aureus.
The frequency of infections caused by multidrug-resistant Staphylococcus aureus continues to increase while the numbers of alternative therapeutic agents remain limited. To investigate the changing patterns of in-vitro susceptibility of S. aureus to 16 antibiotics, 190 clinical isolates from two different years were studied. The MICs of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) strains isolated in 1987 were compared with those of similar numbers of strains isolated in 1989. For MRSA > or = 90% of isolates from both years were resistant to clindamycin, gentamicin and erythromycin. These strains remained highly susceptible to vancomycin (100%), minocycline (90%) and rifampicin (100%). The greatest increase in resistance was observed for ofloxacin (2% in 1987 vs 62% in 1989); cross-resistance to all of the quinolones tested was demonstrated. MSSA strains remained susceptible to vancomycin (100%), minocycline (98%), rifampicin (100%), clindamycin (90%), gentamicin (90%) and ciprofloxacin (98%). It is concluded that methicillin susceptibility is a useful marker for selecting potential agents for the treatment of infections caused by S. aureus. A combination of minocycline and rifampicin may be a useful alternative to vancomycin for treating MRSA infections.
Wadsworth
S J
SJ
Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania.
Kim
K H
KH
Satishchandran
V
V
Axelrod
P
P
Truant
A L
AL
Suh
B
B
D004352:Drug Resistance, Microbial; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D013045:Species Specificity; D013211:Staphylococcus aureus / Q000187:drug effects*