Characterization of a Moraxella species that causes epistaxis in macaques

Bacteria of the genus Moraxella have been isolated from a variety of mammalian hosts. In a prior survey of bacteria that colonize the rhesus macaque nasopharynx, performed at the Tulane National Primate Research Center, organisms of the Moraxella genus were isolated from animals with epistaxis, or "bloody nose syndrome." They were biochemically identified as Moraxella catarrhalis, and cryopreserved. Another isolate was obtained from an epistatic cynomolgus macaque at the U.S. Army Medical Research Institute of Infectious Diseases. Based on differences in colony and cell morphologies between rhesus and human M. catarrhalis isolates, we hypothesized that the nonhuman primate Moraxella might instead be a different species. Despite morphological differences, the rhesus isolates, by several biochemical tests, were indistinguishable from M. catarrhalis. Analysis of the cynomolgus isolate by Vitek 2 Compact indicated that it belonged to a Moraxella group, but could not differentiate among species. However, sequencing of the 16S ribosomal RNA gene from four representative rhesus isolates and the cynomolgus isolate showed closest homology to Moraxella lincolnii, a human respiratory tract inhabitant, with 90.16% identity. To examine rhesus macaques as potential hosts for M. catarrhalis, eight animals were inoculated with human M. catarrhalis isolates. Only one of the animals was colonized and showed disease, whereas four of four macaques became epistatic after inoculation with the rhesus Moraxella isolate. The nasopharyngeal isolates in this study appear uniquely adapted to a macaque host and, though they share many of the phenotypic characteristics of M. catarrhalis, appear to form a genotypically distinct species.