An In Vitro Comparison of Tobramycin and Gentamicin to Moxifloxacin and Gatifloxacin Using Bacterial Keratitis Isolates

Abstract

Abstract: : Purpose: The 4^th generation fluoroquinolones will soon be commercially available. We previously compared 4^th and earlier generation fluoroquinolone activity against bacterial keratitis isolates. To date, no published in vitro comparison of keratitis isolate susceptibility to commonly used aminoglycosides and 4^th generation fluoroquinolones exists. In this study, we compared the susceptibility of clinical bacterial keratitis isolates to tobramycin (Tob), gentamicin (Gent), moxifloxacin (MX), and gatifloxacin (Gat). Methods: The MICs (µg/ml) and susceptibilities of 177 bacterial keratitis isolates were determined for tobramycin, gentamicin, moxifloxacin, and gatifloxacin using Etests and the NCCLS serum standards. The Staphylococcus species and Pseudomonas aeruginosa were subgrouped according to disk diffusion susceptibility to ciprofloxacin and ofloxacin (Qr – fluoroquinolone resistant, Qs – fluoroquinolone susceptible). The bacterial susceptibilities were compared statistically (Chi-square) with significance at p< 0.05. Results: S. aureus Qs (N=25), CoagNeg Staph Qs (25), P. aeruginosa Qs (25), Serratia marcescens (25), Haemophilus spp (10), and Moraxella spp (10) demonstrated equivalent susceptibility to all four antibiotics. The table lists remaining isolate susceptibilities and MICs. Conclusions: The Streptococcus species demonstrated increased susceptibility to MX and Gat over Gent and Tob. S. aureus Qr was more susceptible to MX and Gent than Tob and Gat. Coagulase negative Staphylococci were equivalently susceptible to all four antibiotics, and P. aeruginosa Qr was most susceptible to Tob. No single antibiotic had complete coverage. Clinical studies are needed to confirm our in vitro results. Isolate Susceptibilities and MICs [Percent Susceptible - Median MIC (ug/ml)]  

Keywords: keratitis • bacterial disease • cornea: clinical science