Emergence and acquisition of fluoroquinolone-resistant gram-negative bacilli in the intestinal tracts of mice treated with fluoroquinolone antimicrobial agents.

After mice received orogastric administration of a fluoroquinolone-resistant Klebsiella pneumoniae strain, subcutaneous treatment with ciprofloxacin, levofloxacin, and moxifloxacin promoted persistent low-density colonization in 10% to 40% of the mice, whereas treatment with clindamycin consistently promoted high-density colonization. No emergence of fluoroquinolone-resistant gram-negative bacilli was detected in the mice during or after treatment with the fluoroquinolone antimicrobial agents.