Antimicrobial drug resistance in Corynebacterium diphtheriae mitis

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From: Emerging Infectious Diseases(Vol. 17, Issue 11)
Publisher: U.S. National Center for Infectious Diseases
Document Type: Letter to the editor
Length: 1,243 words
Lexile Measure: 1260L

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To the Editor: Corynebacterium diphtheriae is the agent of pharyngeal and cutaneous diphtheria. We did a retrospective analysis of the antimicrobial drug susceptibilities of 46 C. diphtheriae isolates sent during 1993 through 2010 to the French National Reference Centre of Toxigenic Corynebacteria. The isolates came from metropolitan France and French overseas departments and territories. Only 1 isolate, C. diphtheriae biovar mitis, FRC24, expressed the following anti-microbial drug susceptibility profile: susceptible to penicillin, amoxicillin, ciprofloxacin, clindamycin, erythromycin, gentamicin, imipenem, kanamycin, rifampin, tetracycline, and vancomycin and resistant at an uncommonly high level to trimethoprim, sulfamethoxazole, and co-trimoxazole with Etest (bioMerieux, Marcy l'Etoile, France) MICs of >32, >1,024, and >32 mg/L, respectively.

This FRC24 isolate was isolated in 2008 from a cutaneous wound on a vaccinated 11-month-old child in Mayotte, an overseas department located in the Indian Ocean. Cutaneous carriage of C. diphtheriae is frequent in tropical countries where cutaneous diphtheria is endemic; cutaneous carriage represents a common mode of transmission of the bacterium. FRC24 was identified by using the API Coryne strip (bioMerieux). FRC24 is a toxigenic isolate; toxigenicity was confirmed by both tox gene detection and Elek test (1). Multilocus sequence typing was performed, and the sequence type (ST) of the isolate is ST91. This ST contains only this isolate and is part of lineage II, as are all mitis and gravis biovars (2).

To date, resistance to trimethoprim, sulfamethoxazole, or co-trimoxazole seems to be rare among the C. diphtheriae species, but few data are available (3). As trimethoprim resistance is often encoded by integron-driven dfr determinants, we looked for integrons. Integrons are bacterial genetic elements able to capture and express antimicrobial drug resistance gene cassettes (GCs) (4). GC movements are catalyzed by an integron-encoded integrase IntI. GCs, mainly promoterless, are usually expressed through a common Pc promoter (5). Only rare GCs contain their own promoter (cmlA, qac, ereA1). Three main...

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Gale Document Number: GALE|A272807246