Ability of ciprofloxacin 1g discs and British Society for Antimicrobial Chemotherapy (BSAC) zone diameter breakpoints to detect plasmid-mediated quinolone resistance determinants in urinary enterobacterial isolates

Abstract number: P586

Objectives: Plasmid-mediated quinolone resistance (PMQR) genes have been increasingly reported amongst members of the Enterobacteriaceae worldwide. In London we recently reported an incidence of 53% in a set of ciprofloxacin resistant urinary isolates collected at our centre. As PMQR genes confer only low-level resistance it has been suggested that modification of screening procedures and breakpoints may be required in order to optimize their detection (Cavaco & Aarustrup, JCM 2009). The aim of this study was therefore to determine any correlation between carriage of PMQR genes and zone of inhibition to 1mg ciprofloxacin discs using BSAC susceptibility testing methodology and breakpoints.

Methods: Consecutive non-duplicate enterobacterial isolates obtained from nosocomial and community-acquired urinary tract infections were screened for PMQR genes using primers specific for qnrA,B and S, qepA, and aac(6')-Ib-cr and oqxA,B genes. Antimicrobial susceptibility testing was performed for using the BSAC method with a zone size of leqslant R: less-than-or-eq, slant16 mm considered resistant.

Results: 167 isolates were included, of which 76.0% were identified as Escherichia coli. PMQR genes were found in 37.1% of isolates. qnrS was present in 13.2% of isolates, qnrA in 0.6%, qepA in 2.4%, and aac(6')-Ib-cr in 32.9%. The oqxAB genes were detected in 18 isolates, all of which were identified as K. pneumoniae, in which these genes are located chromosomally Of the isolates harbouring PMQR genes, 98.4% had a zone diameter of leqslant R: less-than-or-eq, slant16 mm to 1mg ciprofloxacin discs.

Conclusions: These results suggest that the BSAC zone diameter breakpoint for 1mg ciprofloxacin discs is adequate to detect isolates with PMQR genes, although a very small proportion of such isolates may be missed.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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