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Aims: WQ-3810 has strong inhibitory activity against Salmonella and other fluoroquinoloneresistant pathogens. The unique potentiality of this is attributed to 6-amino-3,5-difluoropyridine-2-yl at R1 group. The aim of this study was to examine WQ-3810 and its derivatives WQ-3334 and WQ-4065 as the new drugs candidate for wild type Salmonella and that carrying QnrB19. Materials and methods:The half maximal inhibitory concentrations (IC50s) of WQ-3810, WQ-3334 (Br atom in place of methyl group at R8) and WQ-4065 (6-ethylamino-3,5difluoropyridine-2-yl in place of 6-amino-3,5-difluoropyridine-2-yl group at R1) in the presence or absence of QnrB19 were assessed by in vitro DNA supercoiling assay utilizing recombinant DNA gyrase and QnrB19.Results: IC50s of WQ-3810, WQ-3334 and WQ-4065 against Salmonella DNA gyrase were 0.031 ± 0.003, 0.068 ± 0.016 and 0.72 ± 0.39 µg/mL, respectively, while QnrB19 increased IC50s of WQ-3810, WQ-3334 and WQ-4065 to 0.44 ± 0.05, 0.92 ± 0.34 and 9.16 ± 2.21 µg/mL, respectively. Conclusion:WQ-3810 and WQ-3334 showed stronger inhibitory activity against S.Typhimurium DNA gyrases than WQ-4065 even in the presence of QnrB19. The results suggest that 6-amino-3,5-difluoropyridine-2-yl group at R1 is playing an important role and WQ-3810 and WQ-3334 to be good candidates for Salmonella carrying QnrB19.

Aims: Quinolone-resistant nontyphoidal Salmonella having serine replaced by isoleucine at the 83rd. amino acid in GyrA (GyrA-Ser83Ile), has recently been found in Asian countries. Here, we aimed to examine the direct effect of substitution Ser83Ile on DNA gyrase activity and/or resistance to quinolones.Materials and Methods: Using 50% of the maximal inhibitory concentrations (IC50s) of quinolones, recombinant wild type (WT) and seven mutant DNA gyrases having amino acid substitutions, including Ser83Ile, were screened for enzymatic activity that causes supercoils in relaxed plasmid DNA and resistance to quinolones.Results: Little differences in supercoiling activity were observed between WT and mutant DNA gyrases. By contrast, the IC50s of ciprofloxacin and norfloxacin against GyrA-Ser83Ile/WT-GyrB were 11.6 and 73.3 μg/mL, respectively, which were the highest used against the DNA gyrases examined in the present study. Conclusion:Ser83Ile in GyrA was shown to confer high-level quinolone resistance to DNA gyrases of nontyphoidal Salmonella, with no loss of supercoiling activity. Salmonella strain carrying GyrA with Ser83Ile may emerge under a high-concentration pressure of quinolones and easily spread even with no selection bias by quinolones. Hence, avoiding the overuse of quinolones is needed to prevent the spread of Salmonella with Ser83Ile in GyrA.

Background: Leprosy is a chronic infectious disease caused by Mycobacterium leprae and the treatment of choice is ofloxacin (OFX). Specific amino acid substitutions in DNA gyrase of M. leprae have been reported leading to resistance against the drug. In our previous study, WQ-3810, a fluoroquinolone with a new R1 group (6-amino-3,5-difluoropyridin-2-yl) was shown to have a strong inhibitory activity on OFX-resistant DNA gyrases of M. leprae, and the structural characteristics of its R1 group was predicted to enhance the inhibitory activity. Methodology/Principal Finding: To further understand the contribution of the R1 group, WQ-3334 with the same R1 group as WQ-3810, WQ-4064, and WQ-4065, but with slightly modified R1 group, were assessed on their activities against recombinant DNA gyrase of M. leprae. An in silico study was conducted to understand the molecular interactions between DNA gyrase and WQ compounds. WQ-3334 and WQ-3810 were shown to have greater inhibitory activity against M. leprae DNA gyrase than others. Furthermore, analysis using quinolone-resistant M. leprae DNA gyrases showed that WQ-3334 had greater inhibitory activity than WQ-3810. The R8 group was shown to be a factor for the linkage of the R1 groups with GyrB by an in silico study. Conclusions/Significance: The inhibitory effect of WQ compounds that have a new R1 group against M. leprae DNA gyrase can be enhanced by improving the binding affinity with different R8 group molecules. The information obtained by this work could be applied to design new fluoroquinolones effective for quinoloneresistant M. leprae and other bacterial pathogens.