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 25-28 September, 2018 | Singapore
previously uncultured or rarely isolated microbes have been identified, demonstrating that the skin of dogs
is inhabited by diverse microbial communities. Higher microbial diversity was observed in the haired skin (axilla, groin, periocular, pinna, dorsal nose, interdigital, lumbar) compared to mucosal surfaces or mucocutaneous junctions (lips, nose, ear, and conjunctiva). The nostril and conjunctiva showed the lowest, while the axilla
and dorsal aspect of the nose showed highest microbial diversity. On average, around 300 different bacterial genera were identified on the canine dorsal nose. The most abundant phyla across all surfaces were Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes (Rodrigues Hoffmann 2014).
The Skin Microbiome in Cutaneous Disease
The normal skin microbiota is necessary for optimal
skin function, modulating the innate immune response and preventing colonization with potentially pathogenic microorganisms. In many skin conditions, it remains unclear if changes in the microbiome play a causal role in skin diseases or are rather the result of the disease. In humans with atopic dermatitis (AD) and psoriasis,
the changes in the cutaneous microbiome have been proposed to be the result of an altered epidermal barrier function, Toll-like receptor 2 defects, decreases in antimicrobial peptides, and/or increased expression of extracellular matrix proteins. (de Jongh 2005). These mechanisms are thought to be responsible for an increased abundance of Staphylococcus aureus and susceptibility to staphylococcal infections in AD patients.
Similar to humans, dogs develop AD with hypersensitivity to environmental allergens such as house dust mites and/or food allergens. Recurrent infections with Staphylococcus sp. are very common in AD dogs, and in some dogs bacterial products can also trigger lesions of AD, possibly due to an altered epidermal barrier function.
A marked reduction in microbial diversity is observed in children during AD flares, and it is proposed that these changes precede an increase in the severity of AD. The skin microbiome colonizing the haired skin of dogs with allergic skin disease also demonstrates a lower bacterial diversity when compared to the same skin sites (axilla, groin, and interdigital skin) of healthy dogs (Rodrigues Hoffmann 2014). Significant differences in bacterial taxa have been observed between allergic and healthy dogs, especially higher abundance of Betaproteobacteria in the skin of healthy dogs.
Using culture-based methods, the skin and nasal mucous membranes of atopic human patients and dogs are more often colonized with S. aureus and S. pseudintermedius, respectively, than healthy patients. Based on 16S rRNA pyrosequencing data, S. aureus markedly dominated affected skin regions, more commonly the antecubital and popliteal creases, in children with AD. Likewise,
baseline and post flare samples from children with AD also had more abundance of S. aureus compared to the skin of healthy children. Allergen challenge
in experimentally sensitized atopic dogs leads to bacterial dysbiosis with increased abundance of
S. pseudintermedius at the site of lesion induction (Pierezan 2016).
The skin microbiota of atopic dogs has been longitudinally evaluated with parallel assessment
of skin barrier function at disease flare, during antimicrobial therapy, and post-therapy. Sequencing
of the bacterial 16S ribosomal RNA gene showed decreased bacterial diversity and increased proportions of Staphylococcus (S. pseudintermedius in particular) and Corynebacterium species compared with a cohort of healthy control dogs. Treatment restored bacterial diversity with decreased proportions of Staphylococcus species, concurrent with decreased canine atopic dermatitis severity. Skin barrier function, as measured by corneometry, pH, and transepidermal water loss also normalized with treatment. Bacterial diversity correlated with transepidermal water loss and pH level but not with corneometry results (Bradley 2016).
In cAD there is a predisposition to the development
of coagulase-positive Staphylococcus species colonization and dermatitis as in AD. S. aureus is the primary coagulase-positive Staphylococcus species of human skin and mucosal sites. S. pseudintermedius
is a skin and mucosal commensal in the dog and the most frequent pathogen isolated from dogs with skin
or ear canal infections. Human S. pseudintermedius colonization is rare and primarily restricted to those with regular contact with dogs and cats. S. aureus is infrequently isolated from infection and carriage sites of dogs in clinical practice and in epidemiological surveys, and it is considered a comparatively infrequent canine pathogen. The dog may act as a potential vector of
S. aureus, which raises zoonotic and anthropozoonotic concerns for potential transfer of pathogens, drug resistance, and genetic elements.
Microbiomes are often shared between dogs and humans, with pet owners having a more diverse microbiome than non-pet owners. Dogs that cohabit are also likely to have similar microbiomes. These concepts become very important in the context of antimicrobial resistance, where resistance genes can be spread from one bacteria to another and become established within the commensal population.
What is a biofilm?
A bacterial biofilm is a complex, sessile community of bacteria embedded within a self-produced matrix of carbohydrates, proteins and DNA (extracellular polymeric substance, EPS). Within a biofilm, bacteria

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