Isolation and characterization of atypical Riemerella columbina strains from pigeons and their differentiation from Riemerella anatipestifer

Riemerella columbina (RC) and Riemerella anatipestifer (RA) belong to the genus Riemerella within the family Flavobacteriaceae. While RA is a well-described pathogen of waterfowl and other avian species, only little is known about RC. Previous work reporting the isolation of RC from internal organs of clinically diseased pigeons suggested a potential pathogenic role in this avian species. In this study we examined pharyngeal swabs collected from pigeons and found RC to be widely distributed also among healthy birds. Further characterization of 81 RC-isolates revealed several atypical strains, which differed from all previously described RC-isolates by the lack of aesculin-hydrolysis activity (17 isolates) or by expression of yellow or orange pigmentation (6 isolates). Sequence analysis of the 16S rRNA and outer membrane protein A (ompA) gene supported the affiliation of these strains to the species RC. Aesculin-hydrolysis negative isolates were found to be biochemically indistinguishable from RA. We demonstrated that bacterial fingerprinting using matrix assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS) analysis is useful for the identification and differentiation of RC and RA.