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H. Sueke, S. Kaye, C. Parry, S. Tuft, Microbiology Ophthalmic Group; Standard and Novel Topical Antimicrobials for the Treatment of Microbial Keratitis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5946.
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To investigate the minimum inhibitory concentrations (MIC) and synergies of novel and standard antimicrobials on isolates from microbial keratitis.
808 cases of microbial keratitis were included. Bacterial isolates were incubated overnight on media. Single colonies were suspended in sterile water with cotton buds used to streak the inoculum onto agar. E-Tests were applied and plates were incubated. MICs were determined for: ciprofloxacin, chloramphenicol, penicillin, cefuroxime, gentamycin, amikacin, teicoplanin, ofloxacin, levofloxacin, moxifloxacin, linezolid, tigecycline, daptomycin and meropenem.
Results of the MICs that have been collected so far are summarised in the table.Of the S.Aureous group moxifloxacin had the lowest MIC90 (0.063 µg/mL). followed by levofloxacin (0.038 µg/mL) ciprofloxacin and ofloxacin (32µg/mL). This compared well to tigecylcine (0.064µg/mL), linezolid (0.75 µg/mL), penicillin and teicoplanin (1.5µg/mL).Of the P.Aeruginosa isolates: ciprofloxacin, meropenem and levofloxacin had the lowest range and equivalent MIC90 of 0.5µg/mL, which were lower than that of moxifloxacin (1 µg/mL) gentamycin (2 µg/mL) and ofloxacin (1.5 µg/mL). Antibiotics which were resistant with MIC50 >512µg/mL, included linezolid, daptomycin, penicillin, teicoplanin, cefuroxime and chloramphenicol.
Of the S.Aureous isolates, all of the novel antibiotics were susceptible using systemic breakpoint data. Overall Tigecycline had the lowest MICs. In the P.Aeruginosa group, linezolid and daptomycin are completely resistant as they act predominantly against Gram positive organisms. Ciprofloxacin, levofloxacin and meropenem had the lowest MIC50 and MIC90. According to our data the most efficacious antibiotics in treating microbial keratitis according to causative microorganism are: tigecycline for S.Aureous andlevofloxacin, ciprofloxacin or meropenam for P.Aeruginosa.We intend to complete calculating MICs for all 808 isolates and then to assess if any advantage would be gained in using the antibiotics simultaneously in vitro.
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