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Tiago M. Yamanaka, Sr., Paulo J. Bispo, Antonio C. Pignatari, Maria C. Yu, Michel E. Farah, Ana L. Hofling-Lima; Selection Of Fluoroquinolone Resistant Coagulase-negative Staphylocccocus After Moxifloxacin Eye Drops Usage. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1493.
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To determine 8-metoxifluoroquinolone (8-FQ) Minimal Inhibitory Concentration (MIC) and mutations within quinolone-resistant determining region (QRDR) of gyrA and parC genes in coagulase-negative Staphylococcus (CNS) isolated from normal conjunctiva and blepharoconjunctivitis cases after topical use of Moxifloxacin (MX) for one week as well as to compare genetic similarity with pretreatment isolates.
Thirty-four CNS isolates (17 for pretreatment culture and 17 for postreatment) were selected from 15 among 117 patients in the study, 97 patients under treatment for blepharoconjunctivitis and 20 patients that underwent photorefractive keratectomy (PRK). Only post-treatment isolates resistant to 8-FQ were included in the study. Species level identification was accomplished by rpoB gene sequencing. MIC was determined for Gatifloxacin (GX) and MX employing the E-test method. 8-FQ resistant isolates were submitted to gyrA and parC sequencing. The genetic similarity between isolates was evaluated by Pulsed Field Gel Electrophoresis (PFGE).
Seventy-nine point four per cent of CNS were identified as S. epidermidis. Among pretreatment CNS isolates, the susceptibility rate was 88.2% for 8-FQ. Two pretreatment isolates were resistant for 8-FQ. Eight isolates showed high level for MX, and 11 for GX resistance (MIC range 2.0 µg/ml to >32.0 µg/ml) and 9 intermediate resistant for MX and 6 for GX (MIC range 1.0 µg/ml to 1.5 µg/ml). The 8-FQ resistant showed at least one mutation in both gyrA and parC genes. Mainly amino acid substitution was Ser84Phe in the gyrA gene, and Ser80Fen in the parC gene. Different PFGE profiles were observed between strains isolated before and after use of MX recovered from the same patient.
For a minor part of patients, the use of MX can select resistant CNS subpopulation with QRDR mutations that confers 8-FQ resistance.
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