DNA Gyrase and Topoisomerase IV Are Dual Targets of Clinafloxacin Action in Streptococcus pneumoniae

作者：Xiao-Su Pan, L. Mark Fisher · 发表于：Antimicrobial Agents and Chemotherapy · 年份：1998 · DOI：10.1128/aac.42.11.2810 · 被引用次数：214 · 研究领域：Cancer therapeutics and mechanisms、Antibiotics Pharmacokinetics and Efficacy、Pneumonia and Respiratory Infections

We examined the response of Streptococcus pneumoniae 7785 to clinafloxacin, a novel C-8-substituted fluoroquinolone which is being developed as an antipneumococcal agent. Clinafloxacin was highly active against S. pneumoniae 7785 (MIC, 0.125 microg/ml), and neither gyrA nor parC quinolone resistance mutations alone had much effect on this activity. A combination of both mutations was needed to register resistance, suggesting that both gyrase and topoisomerase IV are clinafloxacin targets in vivo. The sparfloxacin and ciprofloxacin MICs for the parC-gyrA mutants were 16 to 32 and 32 to 64 microg/ml, respectively, but the clinafloxacin MIC was 1 microg/ml, i.e., within clinafloxacin levels achievable in human serum. S. pneumoniae 7785 mutants could be selected stepwise with clinafloxacin at a low frequency, yielding first-, second-, third-, and fourth-step mutants for which clinafloxacin MICs were 0.25, 1, 6, and 32 to 64 microg/ml, respectively. Thus, high-level resistance to clinafloxacin required four steps. Characterization of the quinolone resistance-determining regions of the gyrA, parC, gyrB, and parE genes by PCR, HinfI restriction fragment length polymorphism, and DNA sequence analysis revealed an invariant resistance pathway involving sequential mutations in gyrA or gyrB, in parC, in gyrA, and finally in parC or parE. No evidence was found for other resistance mechanisms. The gyrA mutations in first- and third-step mutants altered GyrA hot spots Ser-83 to Phe or Tyr (...