Although the gut microbiome has to date garnered the majority of attention, numerous microbiomes exist on and within the body.1
Microbiomes are present anywhere in the body where microbes reside, including the oral cavity, conjunctiva, external ear, skin, upper and lower respiratory tract, reproductive tract and urinary tract. Body sites differ dramatically in their microbial composition based on the physical and chemical properties of the site, including pH, topography and moisture level.2
Microbiome research in humans is rapidly expanding as investigation into non-gut microbiomes accelerates.
Investigation of non-gut microbiomes in dogs and cats lags behind those of humans, presenting additional opportunities to influence host health.
Despite its physical and functional connection to the gut, the oral microbiome of dogs and cats is a unique microbiome with about 50-100 million bacteria representing approximately 200 species.2-4 Studies to date have shown the oral microbiome of dogs and cats to be comprised of the same dominant phyla, but in different abundances between the species.3,5,6,7 In addition, the microbial population varies with location within the oral cavity.8
The oral microbiome appears to be highly conserved across dogs, with no significant differences between dog breeds.3 In contrast, significant differences in diversity and relative abundance of the oral microbiome were observed between several cat breeds as well as between cats with outdoor exposure and indoor-only cats.9
Alterations in the oral microbiome have been reported associated with birth method (c-section vs vaginal);5 diet format (wet vs dry, as well as changing diet from nursing to commercial food) in cats;5,10 feeding plaque-reducing dental chews to dogs;11 the administration of oral probiotics;12 dental prophylaxis;13 and oral disease (e.g., periodontitis, gingivitis, gingivostomatitis).14-18 However, whether the microbiome alterations precede and predispose to disease, or whether the alterations represent microbial population shifts in response to an altered environment, requires further investigation.3,19,20
Despite documented alterations, the oral microbiome is resilient.3,13
The skin microbiome
The skin microbiomes of dogs and cats are dominated by similar bacterial phyla, but are more diverse than the human skin microbiome.21 As observed in the oral microbiome, the skin microbiome of dogs and cats share the same predominant phyla but in different abundance.21 In both species, haired sites showed a higher number of microbes (richness) than mucosal and mucocutaneous junctions.21 The overall role of the skin microbiome in health and disease is poorly understood,22 but the skin’s role as a primary barrier and its close association with the immune system suggest it is a key player in host health.
The majority of research on the canine and feline skin microbiome has focused on the comparison of healthy and allergic or atopic dogs and cats.
Not surprisingly, research has documented significant differences in the skin microbiome of healthy and allergic cats as well as healthy and allergic or atopic dogs, with reduced diversity and richness associated with allergic and atopic disorders.21,23-26