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B. Ovodenko, D. C. Ritterband, M. K. Shah, J. A. Seedor, R. S. Koplin; Comparison of in vitro Susceptibility Rates of Moxifloxacin and Azithromycin Against Representative Ocular Isolates From 1997-2007. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5531. doi: https://doi.org/.
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To study the in-vitro susceptibility profiles of moxifloxacin and azithromycin against representative conjunctiva strains of S. aureus, S. epidermidis, S. pneumonae, S. viridans, and H. influenza over the past decade.
66 ocular isolates archived at the New York Eye and Ear Infirmary (NYEEI) from 1997-2007 from cases of bacterial conjunctivitis were tested for in vitro susceptibility against moxifloxacin and azithromycin. Etest® antimicrobial gradient strips were used for the quantitative determination of Minimum Inhibitory Concentration (MIC) for each organism. The MIC90 was calculated and reported below. The MIC90 represents the antibiotic concentration that would inhibit the growth of 90% of the tested bacterial isolates. All data was analyzed according to CLSI criteria based on serum concentrations. The archived organisms were subcultured on 5% sheep blood agar. A bacterial suspension was prepared from the subcultures and this suspension was swabbed on a Mueller-Hinton agar plate and incubated for 18-24 hours at 36°C. To facilitate growth, the streptococcus isolates were inoculated on the Mueller Hinton agar plate with 5% sheep blood. Etest® strips were applied and the MIC was read where the inhibition ellipse intersected the scale on the strip.
Of the 66 organisms tested 7 were resistant to both antibiotics. 59 organisms were sensitive to moxifloxacin and 57 organisms were sensitive to azithromycin. The MIC90 against S. aureus was 0.094 µg/ml for moxifloxacin and >256 µg/ml for azithromycin. The MIC90 against Strep viridans was 0.125 µg/ml for moxifloxacin and 4 µg/ml for azithromycin. The MIC90 against H. Influenzae was 0.47 µg/ml for moxifloxacin and 4 µg/ml for azithromycin. There were too few organisms to calculate MIC90 for Strep pneumoniae.
Despite the preferential use of the fluoroquinolone class of antibiotics in ophthalmology over the past decade, moxifloxacin maintains a superior in vitro susceptibility profile with far lower MIC90 values as compared to azithromycin in representative conjunctival strains of S. aureus, S. epidermidis,, S. viridans, and H. influenza.
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