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Selection of resistant variants of respiratory pathogens by quinolones

A M Sefton1, J P Maskell, J D Williams

  • 1Department of Medical Microbiology, St Bartholomew's and the Royal London School of Medicine and Dentistry, UK.

International Journal of Antimicrobial Agents
|July 27, 1999
PubMed

Insights

Fluoroquinolones are effective for community-acquired pneumonia, with low resistance risk in Streptococcus pneumoniae. Enhanced fluoroquinolones show reduced resistance development in key respiratory pathogens.

Area of Science:

  • Microbiology and Infectious Diseases
  • Pharmacology and Drug Resistance

Background:

  • Quinolones are frequently prescribed for respiratory tract infections, including community-acquired pneumonia (CAP).
  • Concerns exist regarding quinolone efficacy against Streptococcus pneumoniae and the potential for rapid emergence of resistance in Enterobacteriaceae.
  • This raises questions about the safety and effectiveness of quinolone treatment for CAP.

Purpose of the Study:

  • To investigate the selection rate of quinolone-resistant variants in key respiratory pathogens.
  • To compare resistance development across different quinolones (nalidixic acid, ciprofloxacin, ofloxacin, levofloxacin) in Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.
  • To assess the risk of resistance emergence during quinolone therapy for CAP.

Main Methods:

  • Tested six strains each of S. pneumoniae, H. influenzae, and M. catarrhalis.
  • Attempted to select for quinolone-resistant variants using nalidixic acid (except for S. pneumoniae), ciprofloxacin, ofloxacin, and levofloxacin.
  • Evaluated the frequency of resistant variant selection and assessed susceptibility according to NCCLS guidelines.

Main Results:

  • Resistant variants of S. pneumoniae were selected at low frequency with ciprofloxacin only, and not with ofloxacin or levofloxacin.
  • Variants of H. influenzae and M. catarrhalis with decreased susceptibility were produced more frequently.
  • Despite decreased susceptibility, H. influenzae and M. catarrhalis variants remained susceptible by NCCLS standards.

Conclusions:

  • Quinolone-resistant variants of S. pneumoniae are unlikely to emerge during treatment.
  • Fluoroquinolones with enhanced Gram-positive activity may further reduce resistance risk.
  • H. influenzae and M. catarrhalis showed increased resistance frequency but remained within susceptible ranges.

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