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ParC and GyrA may be interchangeable initial targets of some fluoroquinolones in Streptococcus pneumoniae
E Varon1, C Janoir, M D Kitzis
1L.R.M.A., Université Paris VI, France.
Abstract:
To evaluate the role of known topoisomerase IV and gyrase mutations in the fluoroquinolone (FQ) resistance of Streptococcus pneumoniae, we transformed susceptible strain R6 with PCR-generated fragments encompassing the quinolone resistance-determining regions (QRDRs) of parC or gyrA from different recently characterized FQ-resistant mutants. Considering the MICs of FQs and the GyrA and/or ParC mutations of the individual transformants, we found three levels of resistance. The first level was obtained when a single target, ParC or GyrA, depending on the FQ, was modified. An additional mutation(s) in a second target, GyrA or ParC, led to the second level. The highest increases in resistance levels were seen for Bay y3118 and moxifloxacin with the transformant harboring a double mutation in both ParC and GyrA. When a single modified target was considered, only the ParC mutation(s) led to an increase in the MICs of pefloxacin and trovafloxacin. In contrast, the GyrA or ParC mutation(s) could lead to increases in the MICs of ciprofloxacin, sparfloxacin, grepafloxacin, Bay y3118, and moxifloxacin. These results suggest that the preferential target of trovafloxacin and pefloxacin is ParC, whereas either ParC or GyrA may both be initial targets for the remaining FQs tested. The contribution of the ParC and GyrA mutations to efflux-mediated FQ resistance was also examined. Active efflux was responsible for two- to fourfold increases in the MICs of ciprofloxacin for the transformants, regardless of the initial FQ resistance levels of the recipients.
Insights
Topoisomerase mutations in Streptococcus pneumoniae confer fluoroquinolone resistance. Multiple mutations in gyrA and parC genes increase resistance, with efflux mechanisms also contributing to reduced susceptibility.
Area of Science:
- Microbiology
- Molecular Biology
- Pharmacology
Background:
- Fluoroquinolones (FQs) are critical antibiotics for treating Streptococcus pneumoniae infections.
- Understanding the genetic basis of FQ resistance is crucial for effective antimicrobial therapy.
Purpose of the Study:
- To investigate the specific roles of topoisomerase IV (parC) and gyrase (gyrA) mutations in mediating FQ resistance in S. pneumoniae.
- To determine the contribution of these mutations to different levels of resistance and identify drug-specific target preferences.
Main Methods:
- Transformation of a susceptible S. pneumoniae strain (R6) with PCR-generated DNA fragments containing quinolone resistance-determining regions (QRDRs) of parC and gyrA from resistant mutants.
- Determination of minimum inhibitory concentrations (MICs) of various FQs for the resulting transformants.
- Analysis of the correlation between specific mutations and observed resistance levels.
Main Results:
- Three distinct levels of FQ resistance were identified, correlating with the number and type of mutations in gyrA and parC.
- Single mutations in either parC or gyrA conferred resistance, with additional mutations leading to higher resistance levels.
- The double mutation in both parC and gyrA resulted in the highest resistance, particularly for Bay y3118 and moxifloxacin.
- Pefloxacin and trovafloxacin primarily targeted ParC, while ciprofloxacin, sparfloxacin, grepafloxacin, Bay y3118, and moxifloxacin could be affected by mutations in either GyrA or ParC.
- Active efflux contributed to a two- to fourfold increase in ciprofloxacin MICs, independent of the target mutations.
Conclusions:
- Mutations in gyrA and parC are key determinants of FQ resistance in S. pneumoniae, with cumulative effects.
- Different FQs exhibit distinct target preferences (ParC vs. GyrA) for initial resistance development.
- Efflux mechanisms play a supplementary role in FQ resistance, enhancing the impact of target mutations.