A new plasmid-mediated gene for quinolone resistance, qnrC

Abstract number: O207

Wang M.H., Xu X., Wu S., Zhu D., Wang M.G.

Objectives: Since the discovery of qnrA in 1998 two additional qnr genes, qnrB and qnrS, have been described. These 3 plasmid-mediated genes contribute to quinolone resistance in Gram-negative pathogens worldwide. A new gene, qnrC, was cloned from a transferable plasmid pHS9.

Methods: Plasmid pHS9 came from a clinical strain of Proteus mirabilis, which transferred low-level quinolone resistance but was negative by PCR for the known qnr genes. Plasmid pHS9 was transferred to azide-resistant E. coli J53 by conjugation. The plasmid was digested by HindIII and a fragment containing the new gene was cloned into plasmid puc18 and sequenced. The ciprofloxacin MICs for clinical and transconjugant strains were determined by Etest.

Results: The strain of P. mirabilis was isolated from an outpatient with a urinary tract infection. It was susceptible to most antimicrobials, but resistant to ampicillin and trimethoprim-sulfamethoxazole. Ciprofloxacin MICs for the clinical strain, J53 R-, and a J53 pHS9 transconjugant were 0.25, 0.008, and 0.125 mg/ml, respectively. A 4.49-kb HindIII fragment of pHS9 was cloned into puc18, and recombinants were transformed into E. coli DH5alpha. Sequencing showed that the responsible 537-bp gene, designated qnrC, encoded a 178 amino acid protein. QnrC shared 67.6%, 48.0% and 63.1% amino acid identity with QnrA1, Qnr B1 and Qnr S1, respectively. An integrase-like gene and an amidase gene were found upstream and downstream from qnrC.

Conclusion: A new quinolone resistance gene, qnrC, was characterised from plasmid pHS9 carried by a clinical isolate of P. mirabilis.