Journal of Antimicrobial Chemotherapy (2002) 49, 917-924
© 2002 The British Society for Antimicrobial Chemotherapy
Molecular characterization of the genes encoding DNA gyrase and topoisomerase IV of Listeria monocytogenes
1Institute of Medical Microbiology and Hygiene, Faculty of Clinical Medicine Mannheim, University of Heidelberg, D-68167 Mannheim, Germany; 2F. Hoffmann-La Roche Ltd, Pharmaceutical Research—New Technologies, CH-4070 Basel, Switzerland
Received 20 August 2001; returned 14 December 2001; revised 7 March 2002; accepted 21 March 2002.
The genes encoding subunits A and B of DNA gyrase and subunits C and E of topoisomerase IV of Listeria monocytogenes, gyrA, gyrB, parC and parE, respectively, were cloned and sequenced. Compared with the sequences of quinolone-susceptible bacteria, such as Escherichia coli and Bacillus subtilis, the quinolone resistance-determining region (QRDR) of DNA gyrase subunit A was altered; the deduced amino acid sequences revealed the substitutions Ser-84
Thr and Asp/Glu-88Phe, two amino acid variations at hot spots, commonly associated with resistance to quinolones. No relevant divergences from QRDR consensus sequences were observed in GyrB or both topoisomerase IV subunits. Thus, it could be argued that the amino acid substitutions in GyrA would explain the intrinsic resistance of L. monocytogenes to nalidixic acid. In order to analyse the actual role of the GyrA alterations, a plasmid-encoded gyrA allele was mutated and transformed into L. monocytogenes. However, these heterodiploid strains were not affected in their resistance to nalidixic acid. The effects of the mutant plasmids on ciprofloxacin and sparfloxacin susceptibility were only modest.
* Correspondence address and present address. Kompetenzzentrum Pathogenomik, Universität Würzburg, Biozentrum, Am Hubland, D-97074 Würzburg, Germany. Tel: +49-931-888-4413; Fax: +49-931-888-4402; E-mail: lampidis{at}biozentrum.uni-wuerzburg.de
Present address. Paul Scherrer Institut, Life Sciences, OSRA/007, CH-5232 Villigen PSI, Switzerland.
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