Xiaoqiang Liu

Publications (2)4.41 Total impact

• Article: In vitro potency and efficacy favor later generation fluoroquinolones for treatment of canine and feline Escherichia coli uropathogens in the United States.

  Xiaoqiang Liu, Dawn M Boothe, Yaping Jin, Kamoltip Thungrat
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  ABSTRACT: Information regarding in vitro activity of newer fluoroquinolones (FQs) is limited despite increasing resistance in canine or feline pathogenic Escherichia coli (E. coli). This study describes in vitro potency and efficacy toward E. coli of seven FQs grouped according to similarities in chemical structure: enrofloxacin, ciprofloxacin, orbifloxacin (first-group), levofloxacin, marbofloxacin (second-group) and pradofloxacin, moxifloxacin (third-group; latest S, S-pyrrolidino-piperidine at C-7). Potency measures included minimum inhibitory concentration (MIC) (geometric mean MIC, MIC(50), MIC(90)); and mutant prevention concentration (MPC) for FQ susceptible isolates only. In vitro efficacy measures included relative susceptibility (MIC(BP-S):MIC) or resistance (MIC:MIC(BP-R)) and mutant selection window (MSW) (MPC:MIC). For enrofloxacin susceptible isolates, mean MIC (μg/ml) was least for each third-group drug and ciprofloxacin and greatest for enrofloxacin and orbifloxacin (P = 0.006). For enrofloxacin susceptible isolates, MPC were below MIC:MIC(BP-R) and least for pradofloxacin (0.29 ± 0.16 μg/ml) and greatest for enrofloxacin (1.55 ± 0.55 μg/ml) (P = 0.006). MSW was least for pradofloxacin (55 ± 30) and greatest for ciprofloxacin (152 ± 76) (P = 0.0024). MIC(BP-S):MIC was greatest (P = 0.025) for pradofloxacin (190.1 ± 0.61) and least for enrofloxacin (23.53 ± 0.83). For FQ susceptible isolates, FQs MIC:MIC(BP-R) may serve as a surrogate for MPC. Because in vitro efficacy was greatest for pradofloxacin; it might be preferred for treatment of urinary tract infections (UTIs) associated with FQ susceptible E. coli uropathogens.
  MIRCEN Journal of Applied Microbiology and Biotechnology 11/2012; · 1.08 Impact Factor
• Article: Mechanisms accounting for fluoroquinolone multidrug resistance Escherichia coli isolated from companion animals.

  Xiaoqiang Liu, Dawn M Boothe, Kamoltip Thungrat, Sherine Aly
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  ABSTRACT: Multidrug resistance (MDR) is associated with fluoroquinolone (FQ) resistance in companion animal Escherichia coli (E. coli). In this study, gyrA, gyrB, parC, and parE quinolone resistance determining regions (QRDR) were sequenced among uropathogenic E. coli isolates with different resistant phenotypes. Also determined were porin, efflux pump and regulatory gene expression based on quantitative real-time reverse transcriptase PCR (qRT-PCR), the impact of efflux pump inhibition (Phe-Arg-β-naphthylamide) and the presence of plasmid-mediated quinolone resistance (PMQR). Using enrofloxacin as the prototypic FQ, we found that (i) the number of mutations in target genes correlate well with minimum inhibitory concentrations (MICs). A single mutation (Ser83Leu) in gyrA increases FQ MIC in susceptible isolates; subsequent mutations result in resistance that increases from low (enrofloxacin MICs 4-16μg/ml) to high level (enrofloxacin MICs≥128μg/ml) with each progressive mutation. (ii) as MIC increase, acrB activity and the number of drug classes contributing to the MDR phenotype increases; (iii) a consistent relationship between regulatory gene expression and MIC could not be identified; and (iv) qnrS and aac(6')-Ib-cr gene were detected in 14 and 5 ENR(R)-MDR isolates containing the target mutation, respectively. Of 13 isolates expressing PDR isolates, 10 (77%) were positive for qnrS gene, and 4 (40%) carried both qnrS and aac(6')-Ib-cr gene. These findings demonstrated that MDR-associated FQ resistance in canine and feline uropathogenic E. coli reflects a combination of point mutations, enhanced efflux pump activities, and PMQR mechanisms. Point mutations in DNA gyrase, however, are necessary to achieve a clinical level of FQ resistance.
  Veterinary Microbiology 07/2012; · 3.33 Impact Factor