Drug resistance of Pseudomonas aeruginosa in vitro evoked by fluoroquinolones

Objective To observe and compare the resistance changes of ciprofloxacin (CIP), levofloxacin (LEV), norfloxacin (NOR) to Pseudomonas aeruginosa (PA), and choose the drug which had the best curative effect for PA from the drugs mentioned above. Methods Seven strain of non-repetitive PA which had sensitiveness to ciprofloxacin (CIP), levofloxacin (LEV), norfloxacin (NOR) and the same minimal inhibitory concentration (MIC) of the three drugs were co-cultured with CIP, LEV, NOR in concentrations of 0.5, 1.0, 2.0, and 4.0 times of MIC for evoked drug resistance, respectively. The MIC of CIP, LEV, and NOR to PA which evoked drug resistance by 3 kinds of concentration were detected by the methods of Epsilometer Test and Two-fold Agar Dilution. Results The MIC value of CIP to PA after evoking by 3 concentrations increased from 0.09 μg/ml before evoking to 0.25-16.00 μg/ml. The MIC after evoking was 3 to 178 times that before evoking. The MIC value of NOR to PA after evoking increased from 0.50 μg/ml before evoking to 2.00-64.00 μg/ml. The MIC after evoking was 4 to 128 times that before evoking. The MIC value of LEV to PA after evoking by 3 concentrations increased from 0.50 μg/ml before evoking to 2.00-32.00 μg/ml. The MIC after evoking was 2 to 64 times that before evoking.The differences of MIC of CIP to PA after evoking by different concentrations of CIP, NOR and LEV were not statistically significant (all P>0.05). The MIC value of NOR to PA after evoking by 4.0×MIC CIP was higher than that of evoking by 0.5×MIC CIP (P=0.006). The MIC value of NOR to PA after evoking by 4.0×MIC LEV was higher than that evoked by 1.0×MIC LEP (P=0.006). The MIC value of LEV to PA after evoking by 4.0×MIC CIP was higher than that of evoking by 0.5×MIC CIP (P=0.006). The MIC value of LEV to PA after evoking by 4.0×MIC NOR and LEV were higher than those evoked by 0.5×MIC NOR and LEV (all P=0.007). Conclusion PA can be evoked to develop resistance to different degrees after co-culturing with different concentrations of CIP, LEV, and NOR. The change of resistance of CIP to PA is the least among the three drugs mentioned above. It is suggested that CIP is still one of the best fluoroquinolones for the treatment of PA infection. Key words: Pseudomonas aeruginosa; Fluoroquinolone; Drug resistance; Microbial sensitivity tests