| Summary: | Background: Polar bears (Ursus maritimus) are major predators in the Arctic marine ecosystem, feeding mainly on seals, and living closely associated with sea ice. Little is known of their gut microbial ecology and the main purpose of this study was to investigate the microbial diversity in faeces of polar bears in Svalbard, Norway (74-81° N, 10-33°E). In addition the level of blaTEM alleles, encoding ampicillin resistance (amp r) were determined. In total, ten samples were collected from ten individual bears, rectum swabs from five individuals in 2004 and faeces samples from five individuals in 2006. Results: A 16S rRNA gene clone library was constructed, and all sequences obtained from 161 clones showed affiliation with the phylum Firmicutes, with 160 sequences identified as Clostridiales and one sequence identified as unclassified Firmicutes. The majority of the sequences (70%) were affiliated with the genus Clostridium. Aerobic heterotrophic cell counts on chocolate agar ranged between 5.0 × 10 4 to 1.6 × 10 6 colony forming units (cfu)/ml for the rectum swabs and 4.0 × 10 3 to 1.0 × 10 5 cfu/g for the faeces samples. The proportion of amp r bacteria ranged from 0 % to 44%. All of 144 randomly selected amp r isolates tested positive for enzymatic b-lactamase activity. Three % of the amp r isolates from the rectal samples yielded positive results when screened for the presence of blaTEM genes by PCR. BlaTEM alleles were also detected by PCR in two out of three total faecal DNA
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