Efficacy of Fourth–Generation Fluoroquinolones Against Pediatric Clinical Isolates of Haemophilus influenzae

Abstract

Purpose: : Haemophilus influenzae is the most common etiologic agent found in pediatric acute conjunctivitis. We investigated the antimicrobial efficacy of fourth–generation fluoroquinolones, gatifloxacin and moxifloxacin, and other antibiotics commonly used to treat pediatric acute conjunctivitis, against pediatric clinical isolates of H. influenzae.

Methods: : 1 x 10⁵colony–forming units (CFU) /mL of pediatric clinical isolates of H. influenzae (isolates B11.2.1.825.3, B11.2.1.209.6, and 11.2.1.5.8) were applied to Mueller Hinton agar. E–test strips containing dilutions in 2–fold increments of gatifloxacin, moxifloxacin, gentamicin, tobramicin, or polymixin B were added, followed by incubation at 37°C in 5% CO₂ for 24 hours. For each drug, the lowest concentration that prevented H. influenzae growth was recorded as the minimal inhibitory concentration (MIC).

Results: : For H. influenzae isolates B11.2.1.825.3 and B11.2.1.209.6, MICs were 0.02 to 0.05 µg/mL for gatifloxacin, 0.1 to 0.2 µg/mL for moxifloxacin, 0.4 to 3.0 µg/mL for polymixin B, 3.0 to 4.0 µg/mL for gentamicin, and 5.0 to 12.0 µg/mL for tobramicin. For H. influenzae isolate 11.2.1.5.8, MICs were 0.08 µg/mL for polymixin B, 0.13 µg/mL for gatifloxacin, 0.19 µg/mL for moxifloxacin, 4.0 µg/mL for tobramicin, and 12.0 µg/mL for gentamicin.

Conclusions: : Gatifloxacin was the most effective antibiotic against 2 of the 3 pediatric H. influenzae isolates tested, showing 4– to 50–fold greater antimicrobial activity than moxifloxacin. The antimicrobial activity of gatifloxacin against the third isolate exceeded that of moxifloxacin by 1.5–fold and was nearly as great as polymixin B. These results suggest that fourth–generation fluoroquinolones, especially gatifloxacin, provide more complete coverage and greater antimicrobial efficacy against clinical H. influenzae strains of pediatric origin than other antibiotics that have traditionally been used to treat pediatric acute conjunctivitis.

Keywords: antibiotics/antifungals/antiparasitics • conjunctivitis • keratitis