Overexpression ofpatAandpatB, Which Encode ABC Transporters, Is Associated with Fluoroquinolone Resistance in Clinical Isolates ofStreptococcus pneumoniae

Abstract

ABSTRACTFifty-seven clinical isolates ofStreptococcus pneumoniaewere divided into four groups based on their susceptibilities to the fluoroquinolones ciprofloxacin and norfloxacin and the dyes ethidium bromide and acriflavine. Comparative reverse transcription-PCR was used to determine the level of expression of the genespatAandpatB, which encode putative ABC transporters. Overexpression was observed in 14 of the 15 isolates that were resistant to both fluoroquinolones and dyes and in only 3 of 24 of those resistant to fluoroquinolones only. Isolates overexpressingpatAandpatBaccumulated significantly less of the fluorescent dye Hoechst 33342 than wild-type isolates, suggesting that PatA and PatB are involved in efflux. Inactivation ofpatAandpatBbyin vitro marinermutagenesis conferred hypersusceptibility to ethidium bromide and acriflavine in all isolates tested and lowered the MICs of ciprofloxacin in thepatAB-overproducing and/or fluoroquinolone-resistant isolates. These data represent the first observation of overexpression ofpatAandpatBin clinical isolates and show that PatA and PatB play a clinically relevant role in fluoroquinolone resistance.