Bacteroides acidifaciens sp. nov., isolated from the caecum of mice.

During studies of the bacterial flora in the intestines of mice, we isolated characteristic strains which lowered the pH of peptone-yeast broth containing Fildes' digest. Based on 16S rRNA sequence comparison, these isolates were considered to belong to the Bacteroides cluster in the bacteroides subgroup of the Cytophaga-Flavobacterium-Bacteroides phylum, and were divided into two groups. Their phenotypic characteristics, i.e. growth in 20% bile, aesculin hydrolysis, and glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activity, were the same as those of the 'Bacteroides fragilis group'. The low level of DNA-DNA hybridization with type strains in the Bacteroides cluster confirmed the novel species status of these isolates. It is proposed that these isolates be named Bacteroides acidifaciens, the type strain of which is A40T (= JCM 10556T).