Abstract
Background: Prevalence of fluoroquinolone-resistant Klebsiella oxytoca has been reported worldwide. Methods: We recovered ten clinical K. oxytoca isolates from patients with acute cystitis, asymptomatic bacteriuria or acute bacillary diarrhea in Japan. Out of ten isolates, one fluoroquinolone-susceptible isolate was included as a control. Fluoroquinolone resistance was characterized genetically by PCR and DNA sequencing methods. Outer membrane protein (OMP) profiles were determined by SDS-PAGE. Results: In nine clinical isolates of levofloxacin-resistant K. oxytoca, nucleotide sequences in the quinolone-resistance-determining regions showed amino acid mutations such as Thr83Ile and Asp87Gly in GyrA and Ser80Ile in ParC. Combined effects of reduced 36-kDa OMP production and amino acid mutations in GyrA and ParC were shown by two K. oxytoca isolates exhibiting higher minimum inhibitory concentrations for fluoroquinolones than other fluoroquinolone-resistant isolates. Conclusions: In clinical K. oxytoca isolates, the various mechanisms of fluoroquinolone resistance may include reduced 36-kDa OMP production as well as GyrA and ParC mutations.
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