Evaluation of Quinolones for detection of acquired quinolone resistance, including the new transmissible resistance mechanisms (qnrA, qnrB, qnrS and aac(6')Ib-cr) in Escherichia coli and Salmonella enterica and determinations of wild type distributions. Journal of clinical microbiology [J Clin Microbiol] Journal article | | Title | Evaluation of Quinolones for detection of acquired quinolone resistance, including the new transmissible resistance mechanisms (qnrA, qnrB, qnrS and aac(6')Ib-cr) in Escherichia coli and Salmonella enterica and determinations of wild type distributions. | | Author(s) | Cavaco LM, Aarestrup FM | | Institution | Research group for Antimicrobial Resistance and Molecular Epidemiology; Department for Microbiology and Risk Assessment; National Food Institute, Technical University of Denmark; Bülowsvej 27; DK-1790 Copenhagen V, Denmark. | | Source | J Clin Microbiol 2009 Jul 1. | | Abstract | Fluoroquinolone resistance in Enterobacteriaceae is mostly due to mutations in the quinolone resistance determining regions (QRDR) of the topoisomerase genes. However, transferable genes encoding quinolone resistance have recently been described. The current methods for susceptibility testing are not adapted to the new resistance determinants which confer low levels of resistance. The aim of this study was to compare the ability of different quinolones in the detection of fluoroquinolone resistance. Sixty-nine Escherichia coli and 62 Salmonella strains including strains fully susceptible to quinolones, nalidixic acid resistant strains, strains with resistance to fluoroquinolones (resistant to nalidixic acid), and strains showing low-level resistance to fluoroquinolones conferred by transferable quinolone resistance genes, including: qnrA, qnrB, qnrS or aac(6')Ib-cr were selected. Disk diffusion assays and MIC determinations by agar dilution method were performed according to CLSI standards for nalidixic acid, flumequine, oxolinic acid, ciprofloxacin, enrofloxacin, marbofloxacin, norfloxacin, ofloxacin and levofloxacin. The MIC of levofloxacin was determined by an E-test. The results showed trimodal distribution of the MIC for both E. coli and Salmonella. The MIC distributions of isolates varied with the tested compounds. Screening for nalidixic acid resistance by MIC testing or disk diffusion was not efficient for the detection of some of the isolates carrying qnr and aac(6')Ib-cr. Transferable resistance genes would be best detected by testing MIC for ciprofloxacin or norfloxacin as the other compounds would fail in the detection of isolates carrying aac(6')Ib-cr, because the enzyme produced is only able to reduce the activity of these two compounds due to their chemical structure. In conclusion, screening with nalidixic acid is efficient for detection of mutants, but for detection of qnr and aac(6')Ib-cr it is not so efficient. Detection would be maximized by screening with either ciprofloxacin or norfloxacin, both in MIC determination or disk diffusion assays. Furthermore, a low concentration of ciprofloxacin (1microg) in the disks seemed to increase the sensitivity of the disk diffusion assay. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 19571019 |
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