The C3H/HeJBir mouse model of intestinal inflammation was used for isolation of a Grampositive, rod-shaped, non-spore-forming bacterium (B7 T) from caecal suspensions. On the basis of partial 16S rRNA gene sequence analysis, strain B7T was a member of the class Actinobacteria, family Coriobacteriaceae, and was related closely to Enterorhabdus mucosicola Mt1B8T (97.6 %). The major fatty acid of strain B7T was C16 : 0 (19.1 %) and the respiratory quinones were mono- and dimethylated. Cells were aerotolerant, but grew only under anoxic conditions. Strain B7T did not convert the isoflavone daidzein and was resistant to cefotaxime. The results of DNA-DNA hybridization experiments and additional physiological and biochemical tests allowed the genotypic and phenotypic differentiation of strain B7T from the type strain of E. mucosicola. Therefore, strain B7T represents a novel species, for which the name Enterorhabdus caecimuris sp. nov. is proposed. The type strain is B7T (=DSM 21839T =CCUG 56815T). © 2010 IUMS.