JAC Advance Access published online on September 30, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn406
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Original research |
Prevalence and distribution of plasmid-mediated quinolone resistance genes in clinical isolates of Escherichia coli lacking extended-spectrum β-lactamases
1 Department of Microbiology, Shrewsbury and Telford NHS Trust, Mytton Oak Road, Shrewsbury SY3 8XQ, UK 2 Department of Medical Microbiology, School of Medicine, University of Manchester, Clinical Sciences Building 1, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK
Received 30 May 2008; returned 7 July 2008; revised 2 September 2008; accepted 3 September 2008
* Correspondence address. Department of Microbiology, Royal Shrewsbury Hospital, Shrewsbury SY3 8XQ, UK. Tel: +44-1743-261161; Fax: +44-1743-261165; E-mail: rod.warren{at}sath.nhs.uk
Objectives: The aac(6')-Ib-cr gene has been described in plasmids from CTX-M-15-producing Escherichia coli in the worldwide ST131 lineage, but has not been systematically sought in other quinolone-resistant strains in the UK. A rise in quinolone resistance in bacteraemia isolates in the UK preceded the increased prevalence of CTX-M-producing strains. This study aimed to describe the presence of plasmid-encoded quinolone resistance genes in historical and current strains of E. coli not producing extended-spectrum β-lactamases (ESBLs).
Methods: Ciprofloxacin-resistant, non-ESBL-producing E. coli isolates included nationally distributed isolates from the BSAC UK bacteraemia surveillance programme between 2001 and 2005, urinary isolates from a regional project in 2000 and local strains in 2006. The aac(6')-Ib-cr gene was detected using PCR followed by restriction fragment length polymorphism analysis. Multiplex PCR was used to detect qnr genes. Isolates with aac(6')-Ib-cr were assessed for aminoglycoside susceptibilities and were serotyped.
Results: The prevalence of the aac(6')-Ib-cr gene was 3% and 9% in current local urinary and historic national bacteraemia quinolone-resistant non-ESBL-producing E. coli, respectively. Of 521 regional urinary E. coli isolates from 2000, 14 were norfloxacin-resistant, none of which carried the aac(6')-Ib-cr gene. National positive bacteraemia isolates from 2001/2 were type O102-ST405 and, in 2004/5, types O1-ST645 and O25-ST131. Positive local urinary isolates from 2006 included serotypes O1 and O25.
Conclusions: In the UK, aac(6')-Ib-cr occurs in E. coli in the absence of CTX-M-15, but with a restricted serotype distribution. Its presence in widespread bacteraemia isolates of a single type from 2001 to 2002, prior to the spread of CTX-M-15 in Britain, might suggest a lineage from which plasmid recombination occurred in man or other species.
Key Words: qnr , aac(6')-Ib , ESBLs