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Journal of Clinical Microbiology, February 2008, p. 527-532, Vol. 46, No. 2
0095-1137/08/$08.00+0     doi:10.1128/JCM.01741-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

High-Level Fluoroquinolone Resistance in Ophthalmic Clinical Isolates Belonging to the Species Corynebacterium macginleyi

Department of Ophthalmology and Visual Neuroscience,¹ Department of Molecular Bacteriology, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan,² Frontier Science Research Center, University of Miyazaki, 5200 Kiyotake, Miyazaki 889-1692, Japan³

Received 31 August 2007/ Returned for modification 17 October 2007/ Accepted 21 November 2007

The clinical importance of nondiphtherial Corynebacterium, a ubiquitous member of the normal human microflora of the skin and mucous membrane, for ocular surface infections has been recognized recently. We performed an antimicrobial susceptibility test with Etest strips for three fluoroquinolones (ciprofloxacin, norfloxacin, and levofloxacin) and a taxonomic analysis on 21 isolates of Corynebacterium from ophthalmic samples. Of these, 16 isolates were identified as C. macginleyi at the species level on the basis of 16S rRNA gene sequence comparisons. The remaining five isolates were determined to be C. mastitidis (four) or C. accolens (one). Eleven of the C. macginleyi isolates showed high levels of resistance to all of the fluoroquinolones tested, and one isolate was resistant to norfloxacin alone. An analysis of the amplified quinolone-resistance-determining regions of the gyrA genes revealed that a single amino acid substitution in position 83 of the gyrA product was sufficient to generate the norfloxacin resistance phenotype, and double mutations leading to amino acid changes in positions 83 and 87 were necessary for high-level resistance against the other fluoroquinolones. We conducted the first example of multilocus sequence typing (MLST) analysis on C. macginleyi. The MLST analysis grouped the majority of C. macginleyi isolates into a single lineage, and another molecular strain typing by random amplified polymorphic DNA fragment patterns supported the finding, indicating that a particular lineage of C. macginleyi is dominant on the human ocular surface. This type of population might be particularly adaptable to the milieu on the human ocular surface.

Published ahead of print on 12 December 2007.