Killing of Streptococcus pneumoniae and Haemophilus influenzae Ocular Isolates by Fourth–Generation Fluoroquinolones

Abstract

Purpose: : Haemophilus influenzae and Streptococcus pneumoniae are fastidious encapsulated organisms that are frequently involved in bacterial conjunctivitis and other ocular infections. We examined the rapidity and efficiency of killing by fourth–generation ophthalmic fluoroquinolones, gatifloxacin 0.3% ophthalmic solution containing benzalkonium chloride 0.005% BAK (Zymar), and self–preserved moxifloxacin 0.5% ophthalmic solution (Vigamox) against H. influenzae and S. pneumoniae ocular isolates.

Methods: : S. pneumoniae and H. influenzae ocular isolates were cultured overnight on blood and chocolate agar, respectively. Colonies were suspended in saline, resulting in an OD₆₅₀ of 0.13–0.15. At time 0, bacterial suspensions were diluted to approximately 5 x 10⁵ CFU/mL in saline containing 0.3% gatifloxacin or 0.5% moxifloxacin, followed by incubation at 37 C. Samples were analyzed for bacterial growth at 5, 10, 15, 30, and 60 minutes. Samples were neutralized for 10 minutes and serially diluted in Dey Engley broth supplemented with 5% Mg⁺⁺ and 3.5% Tween 80. Samples were then filtered and the filters plated on either blood or chocolate agar at 37C for 72 hours before counting.

Results: : No viable S. pneumoniae or H. influenzae were recovered after 5 minutes incubation with gatifloxacin 0.3%. After 10 and 15 minutes incubation in moxifloxacin 0.5%, approximately 10⁴ viable CFU/mL of S. pneumoniae were present, while approximately 10³ CFU/mL remained at 30 minutes incubation. No viable S. pneumoniae were found in 60 minute samples. Incubation with moxifloxacin resulted in a decrease from 10⁵ CFU/ml at 5 minutes to 10²–10³ CFU/ml at 60 minutes with most H. influenzae isolates.

Conclusions: : Gatifloxacin 0.3% preserved with BAK 0.005% (Zymar) killed all ocular isolates strains of H influenzae and S. pneumoniae more rapidly than did moxifloxacin 0.5% (Vigamox), suggesting superior efficacy of gatifloxacin 0.3% ophthalmic solution for these fastidious encapsulated organisms.

Keywords: antibiotics/antifungals/antiparasitics • conjunctivitis • keratitis