Resistance studies with ofloxacin.

Area of Science:

• Microbiology
• Bacterial genetics
• Antimicrobial resistance

Background:

• Ofloxacin is a crucial fluoroquinolone antibiotic.
• Bacterial resistance to antibiotics is a growing public health concern.
• Understanding the mechanisms and frequencies of resistance development is vital.

Purpose of the Study:

• To investigate the selection frequency of ofloxacin-resistant bacterial mutants.
• To compare resistance development across different bacterial species (E. coli, S. aureus, P. aeruginosa).
• To assess the impact of varying ofloxacin concentrations on mutant selection.

Main Methods:

• Single-step passage of bacterial populations at multiples of the Minimum Inhibitory Concentration (MIC).
• Sequential selection of mutants through multiple passages at sub-inhibitory concentrations (1/2 MIC).
• Prolonged exposure of bacterial populations to different ofloxacin concentrations (1, 10, 100 times MIC).

Main Results:

• Low frequency (< 1 x 10^-10) of ofloxacin-resistant mutants in E. coli and S. aureus.
• P. aeruginosa exhibited a higher frequency (3.3 x 10^-8) at 4x MIC, but not at 8x MIC.
• Sequential selection increased MICs by 2- to 32-fold for tested species.
• Mutants were selected in P. aeruginosa at MIC but not at 10x or 100x MIC during prolonged exposure.

Conclusions:

• Bacterial populations exhibit varying frequencies of ofloxacin resistance development.
• Pseudomonas aeruginosa demonstrates a unique resistance selection profile compared to E. coli and S. aureus.
• High concentrations of ofloxacin may prevent the selection of resistant mutants in some species.