Abstract

Background:Anaerotruncus colihomonis is a newly described bacterial genus and species isolated from the stool specimens of children. Its clinical significance, however, is unknown.

Aims: To describe a case of A colihominis bacteraemia identified by 16S ribosomal RNA (rRNA) gene sequencing and provide an emended description of the species.

Methods: An unidentified anaerobic bacillus (strain HKU19) that stains Gram negative was subjected to characterisation by 16S rRNA gene sequencing, G+C content determination and electron microscopy.

Results: Strain HKU19 was isolated from the blood culture of a 78-year-old woman with nosocomial bacteraemia. It was found to be an anaerobic, non-motile, pleomorphic, thin bacillus that stains Gram negative. It produces Indole and utilises glucose and mannose. Identifying the strain to the species level was not possible by conventional phenotypic tests and commercial identification systems. The G+C content of strain HKU19 was found to be 53.43 mol%. A similarity of 99.3% nucleotide identities was found between the 16S rRNA gene sequence of strain HKU19 and that of A colihominis WAL 14 565^T, which was isolated from a human faecal specimen. In contrast with the original description of A colihominis, HKU19 was found to produce occasional oval, terminal spores, although the other phenotypic characteristics matched. Spores were also occasionally observed when the two previously reported strains were re-examined.

Conclusions: Although the source of the bacteraemia in the patient cannot be determined, this report suggests that A colihominis is of clinical significance. Spore formation is proposed as an emended description of A colihominis.