Quinolone resistance mechanisms among extended-spectrum beta-lactamase (ESBL) producing Escherichia coii isolated from rivers and lakes in Switzerland

• Published in: PloS one Vol. 9; no. 4
• Main Authors: Zurfluh, Katrin, Abgottspon, Helga, Hachler, Herbert, Nuesch-Inderbinen, Magdalena, Stephan, Roger
• Format: Journal Article
• Language: English
• Published: Public Library of Science 01.04.2014
• Subjects: Analysis; Beta lactamases; Gene mutations; Quinolone antibacterial agents; Quinolones
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0095864

Sixty extended-spectrum b-lactamase (ESBL)-producing Escherichia coli isolated from rivers and lakes in Switzerland were screened for individual strains additionally exhibiting a reduced quinolone susceptibility phenotype. Totally, 42 such isolates were found and further characterized for their molecular (fluoro)quinolone resistance mechanisms. PCR and sequence analysis were performed to identify chromosomal mutations in the quinolone resistance-determining regions (QRDR) of gyrA, gyrB, parC and parE and to describe the occurrence of the following plasmid-mediated quinolone resistance genes: qepA, aac-6'-Ib-cr, qnrA, qnrB, qnrC, qnrD and qnrS. The contribution of efflux pumps to the resistance phenotype of selected strains was further determined by the broth microdilution method in the presence and absence of the efflux pump inhibitor phe-arg-[beta]-naphthylamide (PAbN). Almost all strains, except two isolates, showed at least one mutation in the QRDR of gyrA. Ten strains showed only one mutation in gyrA, whereas thirty isolates exhibited up to four mutations in the QRDR of gyrA, parC and/or parE. No mutations were detected in gyrB. Most frequently the amino-acid substitution Ser83RLeu was detected in GyrA followed by Asp87 [right arrow] Asn in GyrA, Ser80 [right arrow] Ile in ParC, Glu84 [right arrow] Val in ParC and Ser458 [right arrow] Ala in ParE. Plasmid-mediated quinolone resistance mechanisms were found in twenty isolates bearing QnrS1 (4/20), AAC-6'-Ib-cr (15/20) and QepA (1/20) determinants, respectively. No qnrA, qnrB, qnrC and qnrD were found. In the presence of PA[beta]N, the MICs of nalidixic acid were decreased 4- to 32-fold. (Fluoro) quinolone resistance is due to various mechanisms frequently associated with ESBL-production in E. coli from surface waters in Switzerland.