JAC Advance Access originally published online on December 7, 2005
Journal of Antimicrobial Chemotherapy 2006 57(2):212-220; doi:10.1093/jac/dki443
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Molecular investigation of genetic elements contributing to metronidazole resistance in Bacteroides strains
1 Instutute of Clinical Microbiology, University of Szeged, H-6725 Szeged, Somogyi Béla tér 1, Hungary; 2 Anaerobe Reference Laboratory, Department of Medical Microbiology, University Hospital of Wales, Cardiff, UK; 3 Department of Microbiology, Faculty of Medicine, University of Kuwait, Kuwait
Received 20 July 2005; returned 9 September 2005; revised 2 November 2005; accepted 8 November 2005
* Corresponding author. Tel/Fax: +36-62-545712; E-mail: soki{at}mlab.szote.u-szeged.hu
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
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