A mutation in QRDR in the ParC subunit of topoisomerase IV was responsiblefor fluoroquinolone resistance in clinical isolates of Streptococcus pneumoniae

Forty-one strains of Streptococcus pneumoniae were isolated at Seoul Nation al University Children's Hospital from 1991 to 1997. Isolates were divided into six groups based on MICs of three quinolones, ciprofloxacin, ofloxacin and norfloxacin. Sequencing showed that the isolates which were intermedia tely resistant to three quinolones or resistant to at least one kind of qui nolone had one missense mutation, Lys137 --> Asn (AAG --> AAT) substitution in the ParC subunit of topoisomerase IV without additional mutation in QRD R of the GyrA subunit of DNA gyrase. In conclusion, the ParC subunit of DNA topoisomerase IV is the primary target site for fluoroquinolone in S. pneu moniae and Lys137 --> Asn substitution renders the quinolone resistance in S. pneumoniae..