In vitro activity of levofloxacin, ofloxacin and other quinolones against coagulase-negative staphylococci.
The in vitro activity of levofloxacin against coagulase-negative staphylococci (CNS) was investigated. In vitro, on the basis of MIC90 values, levofloxacin was as active as ciprofloxacin, inhibiting both methicillin-sensitive and -resistant staphylococci at 0.5 microgram/ml. The frequency of one-step development of levofloxacin-resistant CNS was < 1 x 10(-9). After repeated transfer of CNS in the presence of increasing concentrations of levofloxacin or other quinolones, there were 4-fold increases in MIC50 values for both levofloxacin and ofloxacin, whereas there were 64- to 128-fold increases for ciprofloxacin, norfloxacin and enoxacin. Based on MIC50 values, the concentrations of 1 or 2 micrograms/ml are clinically relevant. The mutant strains induced by levofloxacin showed less virulence based on the LD50 value in acute systemic murine infection.
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R. W. Johnson Pharmaceutical Research Institute, Raritan, N.J. 08869.
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D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D003030:Coagulase; D064704:Levofloxacin; D016106:Methicillin Resistance; D051379:Mice; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000494:pharmacology*; D013203:Staphylococcal Infections / Q000188:drug therapy; D013210:Staphylococcus / Q000187:drug effects*; D013212:Staphylococcus epidermidis / Q000187:drug effects; D014774:Virulence
D000890:Anti-Infective Agents; D003030:Coagulase; D064704:Levofloxacin; D015242:Ofloxacin