Laribacter hongkongensis: a potential cause of infectious diarrhea

In this study, we describe the isolation of Laribacter hongkongensis, a recently described genus and species of bacterium, in pure culture on charcoal cefoperazone deoxycholate agar from the stool of six patients with diarrhea. Three patients were residents of Hong Kong, and three of Switzerland. In none of the stool samples obtained from these six patients was Salmonella, Shigella, enterohemorrhagic Escherichia coli, Vibrio, Aeromonas, Plesiomonas, or Campylobacter recovered. Rotavirus antigen detection, electron microscopic examination for viruses, and microscopic examinations for ova and cysts were all negative for the stool samples obtained from the three patients in Hong Kong. Enterotoxigenic E. coli was recovered from one of the patients in Hong Kong. Unlike L. hongkongensis type strain HKU1, all the six strains were motile with bipolar flagellae. Sequencing of the 16S ribosomal RNA genes of the six strains showed that they all had sequences with only 0-2 base differences to that of the type strain. Pulsed field gel electrophoresis of the SpeI digested genomic DNA of the six isolates and that of the type strain revealed that the seven isolates were genotypically unrelated strains. More extensive epidemiologic studies should be carried out to ascertain the causative association between L. hongkongensis and diarrhea and to define the reservoir and modes of transmission of L. hongkongensis.