Abstract

The aim of this study was to examine the in vitro antibacterial activity of WQ-3810, a new fluoroquinolone, against clinically relevant pathogens such as Acinetobacter baumannii, Escherichia coli and Streptococcus pneumoniae, including multidrug-resistant (MDR) and fluoroquinolone-resistant (FQR) isolates, compared with those of ciprofloxacin, levofloxacin, moxifloxacin and gemifloxacin. WQ-3810 demonstrated the most potent activity against the antimicrobial-resistant pathogens tested. Against A. baumannii, including MDR isolates, the potency of WQ-3810 [minimum inhibitory concentration for 90% of the organisms (MIC90)=1mg/L] was more than eight-fold higher than that of ciprofloxacin (64mg/L) and levofloxacin (8mg/L). Against E. coli and S. pneumoniae, including FQR isolates, WQ-3810 (MIC90=4mg/L and 0.06mg/L, respectively) was also more active than ciprofloxacin (64mg/L and 2mg/L) and levofloxacin (32mg/L and 2mg/L). Furthermore, WQ-3810 was the most potent among the fluoroquinolones tested against meticillin-resistant Staphylococcus aureus (MRSA) and Neisseria gonorrhoeae, including FQR isolates. In particular, WQ-3810 demonstrated highly potent activity against FQR isolates of A. baumannii, E. coli and S. pneumoniae with amino acid mutation(s) in the quinolone resistance-determining region of DNA gyrase and/or topoisomerase IV, which are the target enzymes of fluoroquinolones. An enzyme inhibition study performed using FQR E. coli DNA gyrase suggested that the potent antibacterial activity of WQ-3810 against drug-resistant isolates partly results from the strong inhibition of the target enzymes. In conclusion, this study demonstrated that WQ-3810 exhibits extremely potent antibacterial activity over the existing fluoroquinolones, particularly against MDR and FQR pathogens.

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