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High-level fluoroquinolone resistance in Streptococcus pneumoniae requires mutations in parC and gyrA
C Janoir1, V Zeller, M D Kitzis
1L.R.M.A., Université Paris VI, France.
Abstract:
The mechanism of high-level fluoroquinolone resistance was studied in strains of Streptococcus pneumoniae, either selected in vitro or isolated from clinical samples. By using DNA from these high-level-resistant strains, low-level-resistant transformants (MIC of pefloxacin, > or = 32 micrograms/ml; MIC of ciprofloxacin, 4 micrograms/ml; MIC of sparfloxacin, 0.50 micrograms/ml) were obtained at high frequencies (ca.10(-2)), while high-level-resistant transformants (MIC of pefloxacin, > or = 64 micrograms/ml; MIC of ciprofloxacin, 16 to 64 micrograms/ml; MIC of sparfloxacin, > or = 8 micrograms/ml) were obtained only at low frequencies (ca.10(-4)). This suggested that mutations in at least two unlinked genes were necessary to obtain high-level resistance. Low-level resistance was associated with ParC mutations (change from Ser to Tyr at position 79 [Ser79Tyr], Ser79Phe, or Asp83Gly). ParC mutations were associated, in high-level-resistant strains and transformants, with alterations in the quinolone resistance-determining region of GyrA (Ser84Tyr, Ser84Phe, and/or Glu88Lys). Low-level resistance was shown to be necessary for expression of the gyrA mutations. No mutation in the region corresponding to the quinolone resistance-determining region of GyrB and no alteration of drug accumulation were found.
Insights
High-level fluoroquinolone resistance in Streptococcus pneumoniae requires mutations in at least two genes. Low-level resistance, driven by ParC mutations, is essential for the expression of high-level resistance mediated by GyrA mutations.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Fluoroquinolones are crucial antibiotics for treating Streptococcus pneumoniae infections.
- Understanding resistance mechanisms is vital for effective treatment strategies.
- High-level resistance necessitates investigation into genetic underpinnings.
Purpose of the Study:
- To elucidate the genetic mechanisms conferring high-level fluoroquinolone resistance in Streptococcus pneumoniae.
- To identify specific mutations associated with varying levels of resistance.
- To determine the relationship between mutations in different genes.
Main Methods:
- In vitro selection and genetic transformation of Streptococcus pneumoniae strains.
- Analysis of DNA from resistant strains to generate transformants.
- Determination of minimum inhibitory concentrations (MICs) for fluoroquinolones.
- Sequencing of quinolone resistance-determining regions of gyrA and parC genes.
Main Results:
- Low-level fluoroquinolone resistance was achieved via ParC mutations (Ser79Tyr, Ser79Phe, Asp83Gly).
- High-level resistance required additional mutations in the GyrA gene (Ser84Tyr, Ser84Phe, Glu88Lys).
- Low-level ParC mutations were necessary for the expression of high-level resistance conferred by GyrA mutations.
- No mutations were found in GyrB or alterations in drug accumulation.
Conclusions:
- High-level fluoroquinolone resistance in Streptococcus pneumoniae is a multi-step process involving mutations in at least two unlinked genes.
- ParC mutations confer low-level resistance and are a prerequisite for the development of high-level resistance.
- GyrA mutations, in conjunction with ParC mutations, are responsible for high-level fluoroquinolone resistance.