Prevalence of nim-genes in Bacteroides fragilis group in Belgium

Abstract number: P2039

Wybo I., Soetens O., Van Doorslaer K., Piérard D., Lauwers S.

Objectives: Metronidazole resistance among anaerobic Gram-negative bacilli remains low and below 1 percent in species of the B. fragilis group [1] in Belgium. This resistance has been shown to be associated with nitroimidazole (nim) resistance genes. The presence of a nim gene does not necessarily confer metronidazole resistance as nim genes have been detected in B. fragilis group isolates that have a MIC below 16 mg/L and are therefore considered susceptible. High level metronidazole resistance can however be induced in nim-gene-carrying B. fragilis group strains. The purpose of this study was to determine the prevalence of nim genes in isolates belonging to the B. fragilis group isolated in Belgium.

Methods: From October 2003 to February 2005 238 B. fragilis group strains were collected in 9 Belgian hospitals [1]. Metronidazole susceptibility was determined by Etest®. The strains were screened for nim genes by PCR with specific primers. When positive, sequencing of the PCR product was performed.

Results: Nim genes were detected in 5/135 (3.7%) of B. fragilis strains and 1/103 (0.97%) of other B. fragilis group strains. They were not found in isolates with a MIC less than 2 mg/L. Of isolates with MIC higher than 1 mg/L 62.5% (5/8) B. fragilis strains and 20% (1/5) other B. fragilis group strains were nim gene positive. The only metronidazole resistant B. fragilis isolate (MIC=32 mg/L) carried the nimA gene. All other nim-gene carrying B. fragilis isolates (2 nimD, 1 nimB and 1 nimE) were susceptible, but with relatively high MIC values (3 with MIC=4 mg/L and 1 with MIC=2 mg/L). In the other B. fragilis group strains one B. vulgatus isolate carried the nimD gene and had a MIC of 4 mg/L. The only metronidazole resistant strain (MIC=32 mg/L) in this group was a nim gene negative B. thetaiotaomicron isolate. This either suggests the presence of another resistance mechanism in this strain or the presence of a nim gene, that was not detected with the PCR assay used.

Conclusion: Nitroimidazole (nim) resistance genes were present in 2.5%B. fragilis group clinical isolates in Belgium and associated with higher MIC values (range: 2–32 mg/L). The prevalence of nim-genes in B. fragilis group clinical isolates in Belgium is comparable with the prevalence other European countries.


1. Wybo. I. et al. Third Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria. Journal of Antimicrobial Chemotherapy 2007; 59: 132–9.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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