Selection of a gyrA Mutation and Treatment Failure with Gatifloxacin in a Patient with Streptococcus pneumoniae with a Preexisting parC Mutation

Authors


Michael B. Kays, Pharm.D., Department of Pharmacy Practice, Purdue University School of Pharmacy and Pharmaceutical Sciences, W7555 Myers Building, WHS, 1001 West Tenth Street, Indianapolis, IN 46202–2879; e-mail: mkays@iupui.edu.

Abstract

An 81-year-old woman had pneumonia caused by Streptococcus pneumoniae (levofloxacin Etest minimum inhibitory concentration [MIC] 1.5 μg/ml) and was treated with intravenous gatifloxacin 200 mg/day. After 3 days of therapy, repeat sputum cultures were positive for S. pneumoniae, which was resistant to levofloxacin (Etest MIC > 32 μg/ml). The isolate obtained before therapy showed a preexisting parC mutation of aspartic acid-83 to asparagine (Asp83→Asn), and the isolate obtained during therapy showed an acquired gyrA mutation from serine-81 to phenylalanine (Ser81→Phe) and a second parC mutation from lysine-137 to Asn (Lys137→Asn). Both isolates were the same strain, as determined with pulsed-field gel electrophoresis. This case demonstrates the potential for resistance to emerge during 8-methoxy fluoroquinolone therapy for fluoroquinolone-susceptible S. pneumoniae with a preexisting parC mutation. Additional clinical failures with a fluoroquinolone may occur unless these first-step parC mutants can be identified to assist clinicians in selecting appropriate antimicrobial therapy.

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