Journal Article

Molecular investigation of genetic elements contributing to metronidazole resistance in <i>Bacteroides</i> strains

József Sóki, Micaela Gal, Jon S. Brazier, Vincent O. Rotimi, Edit Urbán, Elisabeth Nagy and Brian I. Duerden

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 57, issue 2, pages 212-220
Published in print February 2006 | ISSN: 0305-7453
Published online December 2005 | e-ISSN: 1460-2091 | DOI:
Molecular investigation of genetic elements contributing to metronidazole resistance in Bacteroides strains

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Objectives: The aim of this study was to investigate the constitution of nim gene types, their activating insertion sequence (IS) element, their localization (plasmid or chromosome) and cfiA gene status in metronidazole-resistant Bacteroides strains (n = 26) in order to examine their interchangeability.

Methods: Southern hybridization and conjugative plasmid transfer were used to localize the nimA–E genes and plasmid functions. PCR was used to detect the IS elements and the cfiA genes. PCR-mapping was applied to detect the nim gene-associated IS elements. PCR-mapping products and a nimE gene-containing plasmid fragment were sequenced.

Results: Nine of the nimA genes (12) were activated by IS1168 and nine were carried on plasmids, four of which were pIP417-like. The five nimB genes were chromosomal, and two of them were associated with IS1168 and one with IS612. Of the three nimC genes, two were activated by IS1170, and one was carried on a pIP419-like plasmid. The only nimD gene was chromosomal. The five nimE strains harboured the resistance genes on plasmids: one plasmid, pBF388c, 8.3 kb, was characterized, and a novel IS-like element was demonstrated upstream of all the nimE genes. The insertion events of some of these IS elements were restricted to certain nim gene-specific positions. The 11 chromosomal nim genes displayed a positive association with the cfiA gene-specific background.

Conclusions: Fourteen strains harboured the well-known genetic elements: pIP417- and pIP419-like plasmids, chromosomal nimB genes and a common nimE plasmid. However, a rate of interchangeability was also demonstrated, mostly due to combinations of nim genes and their associated IS elements harboured on different replicons.

Keywords: nim genes; insertion sequence (IS) elements; cfiA; plasmid functions

Journal Article.  5778 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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