Levofloxacin selects fluoroquinolone-resistant methicillin-resistant Staphylococcus aureus less frequently than...

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen causing difficult-to-treat infections.
• Fluoroquinolones, including ciprofloxacin and levofloxacin, are crucial for treating MRSA infections.
• Understanding the mechanisms and rates of resistance development is vital for effective antimicrobial stewardship.

Purpose of the Study:

• To compare the in vitro frequency of resistance development to ciprofloxacin versus levofloxacin in MRSA.
• To investigate the impact of serial passage on the minimum inhibitory concentrations (MICs) of these antibiotics against MRSA.

Main Methods:

• Seventeen unique MRSA strains were used to determine single-step resistance rates to ciprofloxacin and levofloxacin.
• Strains were serially passaged in vitro to assess the development of resistance and changes in MICs.
• Resistance rates and MIC changes were statistically analyzed.

Main Results:

• The mean single-step resistance rate to ciprofloxacin was significantly higher than to levofloxacin (1.05 x 10(-5) vs. 4.03 x 10(-6), P < 0.05).
• Serial passage led to a greater mean increase in ciprofloxacin MIC (3.0-fold) compared to levofloxacin MIC (1.8-fold) (P < 0.05).
• More strains developed resistance to ciprofloxacin (eight) than to levofloxacin (four) during serial passage (P < 0.05).

Conclusions:

• Ciprofloxacin selects for resistant MRSA more frequently than levofloxacin.
• These findings suggest a higher propensity for resistance development with ciprofloxacin, impacting treatment strategies for MRSA infections.