The strict tropism of many pathogens for man hampers the development of animal models that recapitulate important microbehost interactions. We developed a rhesus macaque model for studying Neisseria-host interactions using Neisseria species indigenous to the animal. We report that Neisseria are common inhabitants of the rhesus macaque. Neisseria isolated from the rhesus macaque recolonize animals after laboratory passage, persist in the animals for at least 72 d, and are transmitted between animals. Neisseria are naturally competent and acquire genetic markers from each other in vivo, in the absence of selection, within 44 d after colonization. Neisseria macacae encodes orthologs of known or presumed virulence factors of human-adapted Neisseria, as well as current or candidate vaccine antigens. We conclude that the rhesus macaque model will allow studies of the molecular mechanisms of Neisseria colonization, transmission, persistence, and horizontal gene transfer. The model can potentially be developed further for preclinical testing of vaccine candidates.commensal Neisseria | nonhuman primate model | type IV pili M icrobe-host interactions are often refractory to investigation because of the exquisite tropism of many bacteria for the human host. Host-restriction has prevented the development of animal models that recapitulate colonization, transmission, and persistence; hampered studies of horizontal gene transfer (HGT); and prevented preclinical testing of vaccine candidates. One means to circumvent host restrictions is to develop an animal model of infection using a related species indigenous to that animal. For example, infections by human pathogens, such as Bordetella pertussis and Chlamydia trachomatis, have been effectively modeled in animals with Bordetella bronchiseptica and Chlamydia muridarum, respectively (1, 2).The genus Neisseria and the rhesus macaque provide us with this opportunity. Neisseria are Gram-negative, diplococcal β-Proteobacteria. This genus includes >10 human-adapted species, two of which are pathogens, and an unknown number of species that naturally colonize animals. These species are highly related: >40% of the genes in pathogenic species are also present in commensals, and many of these encode virulence genes and antibiotic resistance alleles. The species are naturally competent and transfer genetic information to each other in vitro (3, 4). HGT is widely assumed to play an important role in the spread of antibiotic resistance among pathogenic Neisseria; however, there is little information on the extent to which HGT occurs in vivo.Pathogens Neisseria meningitidis and Neisseria gonorrhoeae have an exquisite tropism for man. These pathogens do not naturally infect animals; inoculated into nonhuman hosts, the pathogens will colonize only for brief periods (5, 6). Neisseria species have been isolated from a number of animals (7-10), suggesting it may be possible to develop a model for studying Neisseria-host interactions in which there are no host-restriction barriers to overcome.The ...