The examination of qnr and aac(6')- I b-cr genes of clinical isolates resistant to ciprofloxacin in Enterobacteriaceae
Objective To investigate the distribution of qnr and aac(6')- Ⅰ b-cr genes of clinical isolates resistant to ciprofloxacin in Enterobacteriaceae in Wenzhou. Methods From August 2005 to April 2008 a total of 461 clinical isolates resistant to ciprofloxacin in Enterobacteriaceae (370 isolates of Escherichia coli, 39 isolates of Enterobacter cloacae and 52 isolates of Klebsiella) were collected from the First Affiliated Hospital of Wenzhou Medical College. qnr and aac(6')- Ⅰ b genes were detected by PCR for all the clinical isolates, DNA sequencing was used for qnr and aac(6')-Ⅰ b-cr identification and conjugation experiment was proved to find ways of transmission of antimicrobial resistance. Results Fifteen qnr-positive isolates were detected among 461 Enterobacteriaceae isolates, including 5 qnrA-positive isolates (4 Enterobacter cloacae isolates and 1 Klebsiella ornithinolytica isolate), 4 qnrB-positive isolates( 2 Klebsiclla paeunoniae isolates and 2 Escherichia coli isolates), 6 qnrS-positive isolates(2 Klebsiella pneunoniae isolates and 4 Escherichia coli isolates). Fifty-two among 461 Enterobacteriaceae isolates harbored aac(6')- Ⅰ b-cr gene, including 42 Escherichia coil isolates, 4 Enterobacter cloacae isolates and 6 Klebsiella isolates. DNA sequencing for 15 qnr-positive isolates found they harbored aac(6')- Ⅰ b-cr gene simultaneously. Fifteen qnr-positive isolates were susceptible to imipenem but resistant to some other drugs. Conjugation experiments were successfully carried out in 7 of 15 isolates harbored qnr and aac(6')-Ⅰ b-cr genes, and their resistance to quinolones and aminoglycosides was partly transmitted to the recipient isolates. Conclusion The qnr genes are few in clinical isolates resistant to ciprofloxaein in Enterubacteriaceae in Wenzhou, however the aac(6')- Ⅰ b-cr gene is popular. 
 
Key words: 
Enterubacteriaceae;  Plasmid;  qnr gene;  aac(6')- Ⅰ b-cr gene