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Canine Atopic Dermatitis (Eczema) and the Microbiome

Updated: Apr 27, 2023


The gut microbes are a cause of inflammation, including a multifactorial clinical condition called atopic dermatitis (eczema) which affects 10-15% of all dogs. The symptoms are inflamed skin and itching and whilst it isn’t life-threatening the dog may have regular uncomfortable flare-ups as the condition moves on to become a chronic syndrome. Exploring the links between the gut bacteria and skin conditions such as eczema is now possible, but before we can define how the gut microbial community becomes imbalanced to detrimentally affect health and cause disease, it’s worth taking a look at how they live together to benefit the host. If we can learn how to keep the microbial communities balanced, then we can identify and provide therapies/remedies/dietary changes to prevent the onset of man disease states including eczema.

How microbes live together.

Microbes have evolved with their host over hundreds of years, core members of the community are passed on at birth and the gut is largely fully populated during the first year, though percentages of the community will change throughout the life of the dog.

The microbiome is all about relationships and action. Relationships create stability within the biome and the actions (digestion, fermentation, breakdown, manufacturing) provide the host with health benefits in the form of energy or alternatively, disease when the stability of the biome is lost, creating opportunities for inflammation and infection.

Microbes have five different types of relationship

1. Mutualism- The host uses the gut bacteria to digest difficult food items such as bones in the case of dogs, he then receives energy and nutrients from the process and the gut bacteria get a place to live and sometimes even a share in the nutrients.

2. Amensalism- when one species of bacteria is inhibited or destroyed, and another species is unaffected by the interaction. An example would be when a beneficial strain of Lactobacillus interacts with a pathogenic (bad) bacteria called Pseudomonas (Garcia et al., 2017). Lactobacillus suffers no ill harm whilst Pseudomonas is badly disabled/killed off by the lactobiotic acid produced during the encounter. Therefore, having enough pathogen-killing lactobacillus provides protection against the onset of infections.

3. Commensalism- A commensal bacteria consume the food ingested by the host, does no harm to the host, but may send out protective signals to the host immune system in the presence of a high number of pathogenic bacteria. Can also produce antimicrobial substances to prevent the overgrowth of pathogens.

4. Competition – the gut biome is a very competitive place, fighting over resources is necessary for survival and produces genetic persistence. Survival instincts produce symbiotic relationships, prompting a reliance on allies and including ferocious fighting over resources such as nutrients, light or territory. Some species of bacteria can be passively competitive, producing enzymes to hinder or harm opposing species of bacteria.

5. Predation and parasitism- where one species of bacteria gets to benefit from another. A consummate predator and common member of the canine microbiome is Bdellovibrio bacteriovorus. Bdellovibrio kills its prey by punching holes in it, extracting building blocks to help in self- replication, and suffering no ill effect or harm to itself during the process. Because Bdellovibrio has multiple functions the prey is unable to evolve a resistant strategy, making this species a possible and viable replacement for antibiotics.

New technology allows us to expand and explore the microbial communities that reside both inside (in the gut) and outside (skin, ears) of our dogs. PetBiome have used this technology to develop a test that produces a report relating to the microbial relationships described above and provides links to the health benefits of the bacteria such as gut wall integrity and immune response.

The report also contains an array of other important health information relating to the immune system and food allergies, allowing pet owners to manage pet care/health in a proactive and prophylactic way, taking the guesswork out of what to feed and providing important insight into many of today’s complicated chronic syndrome diseases. view report

How do the microbes within the gut connect to the skin?

The dog has a different microbial community residing on the skin and in the ear, urinary and respiratory tracts, the different sites are ecosystems each with a common core membership formed from a mutually beneficial relationship with the host developed over hundreds of years. Microbes are sensitive to change and imbalances called dysbiosis are common, causing infections and inflammation both at site and within the gastrointestinal microbial community.

In other words, diseases of the skin can be linked back to gastric disturbances and imbalances through the skin/gut axis, the gut bacteria communicating through the endocrine, immune, and nervous systems.

The gut microbes are linked to many different types of inflammation including atopic dermatitis (eczema). Science has identified multiple reasons for the onset of eczema in dogs including the breakdown of the skin barrier, poor immune system response, and alterations to the skin microbiome. Human research into the same condition has identified dysbiosis of the gut microbial communities and results from a recent dog trial have found the same is true.

One of the main findings in the 2022 dog preliminary trial (Rosthaher, et al., 2022) was a significantly reduced alpha -diversity score amongst the dogs with atopic dermatitis. Alpha diversity is an ecological term used to describe the total average of all identified species within the gut rather than simply a count of the number of species within the gut, which is termed species richness.

The main cause for a reduction in alpha diversity is thought to be the wide use of medication such as antibiotics which reduce the numbers of predator bacteria that kill pathogenic bacteria linked to disease, such as Escherichia Coli. In the absence of predator bacteria, the pathogenic bacteria multiply and translocate across the gut wall to cause problems in other parts of the body or produce inflammation and reduced immune response.

The Phylotype of Atopic Dermatitis

Using new sequencing technologies and then incorporating the large data into AI and M/L to look for patterns of relationships (Zeng et al., 2021) it has been possible to put together a microbial profile of dysbiosis in dogs with atopic dermatitis. We have our own population data set of dogs, 12% of which have a veterinary diagnosis of atopic dermatitis. The profile developed at Petbiome has found a similar drop in alpha diversity in affected dogs, though the profiles differ slightly from the published paper, the differences possibly reflecting different environments, the database dogs are from the UK.

All affected dogs had significantly raised levels of Conchiformibius from the family Neisseraceae, Catenibacterium, Ruminococcus, and Megamonas, all have been previously studied in dogs and linked to weight loss, parvovirus infections, and prebiotic use.

Reduced levels of bifidobacteria and lactobacillus in humans with atopic disease, are both recognised as components of eczema; however, the 3 affected dogs used in the 2022 study did not have lower levels.

Bifidobacteria is widely recognised as being an important member of the human microbiome but low levels in dogs seem to be more common as evidenced in a 2017 trial (Masuoka et al.,2017) and as per our own database, where 70% of all dogs had low bifidobacteria. The same trial found lactobacillus to be more important to dog health than bifidobacteria and using findings from our own database we can concur there are more links to disease in dogs with lower levels of lactobacillus.

Using the Phylotype pattern produced from our database and identified by the study it is then possible to develop effective management/dietary therapies to help restore the balance to the microbial community which in turn supports the normal functioning of the skin and immune system.

The Phylotype Diet

A medium to large dog will consume 2 tons of food in his lifetime (imperial tons, 20kg dog, 15-year lifespan) and the gastrointestinal tract is the interface where the food/environment interacts with the host. The microbes in the gut sort, manage, breakdown, and signal the host based on the food consumed and the environment the animal resides in, hence knowledge of the interaction between food and gut microbe interaction is crucial.

The microbiome manages and shapes the immune system, it protects against pathogens and biofilm formation, and produces secondary chemicals and maintains the gut wall barrier ensuring health to its host.

The microbiome is a finely balanced ecosystem and is sensitive to changes of diet, environment, and food contamination, it is especially sensitive to medication. Antibiotics are antimicrobial in action and will kill off the good and bad bacteria indiscriminately, reducing the nutrients available to the host and creating an imbalance (dysbiosis) favouring the formation of biofilm/pathogen bacteria that reduce immune system response and cause inflammation.

There are 2 clear goals for managing the health of gut microbial communities

  • Increase diversity

  • Reduce the bad pathogenic bacteria and those that create biofilms.

Dietary Changes.

  • To increase diversity dietary changes would include an increase in food items that are unprocessed and varied, including some plant materials that are high in polyphenols. Variety creates a stable microbiome, unprocessed food (especially fibre) provides the gut bacteria with rapidly digested carbohydrates but does not provide the specialist bacteria and fungi with the hard-to-digest type of fibre they need. Allowing the dog access to outside activities such as digging holes in the garden and burying bones is a sure way to repopulate the gut with friendly microbes. view PetBiome Prebiotic

  • Medicinal plants can be highly effective at reducing the number of pathogenic gut bacteria without harming the good bacteria (Castronovo et al., 2021). Plants contain hundreds of secondary metabolite compounds, often called antioxidants, with antimicrobial properties. A good example is tannin, a phytochemical able to pass through the bacterial cell wall, and interfere with the metabolism, resulting in the death of the bacteria. There is extensive research supporting the use and benefit of phytonutrients to help rebalance the microbiome, more posts to come. View PetBiome Biotic Boost

How to use the PetBiome analysis to support diet/health management.

We know how complex and inter-relational the microbes in the biome are and how sensitive the community is to change and how having a prior medication history may have caused a loss of biodiversity and instability. Identifying the population, especially in relation to improving the diversity score through an increase in the numbers of good gut bacteria will be a huge benefit to deciding how to feed for optimum gut health.

Each dog is an individual and their microbiome differs according to diet, breed and age it’s important to consider these differences within the microbial population before deciding how to manage the health of your pet. For instance, a dog on a raw diet will have a different microbiome from a dog on a kibble diet, though the goals are the same ie. to improve diversity and reduce the bad bacteria, the approach and therapies will differ.

There is a section within the report that generates your pet’s Phenoprofile in relation to the bacteria identified in the microbiome of dogs with atopic dermatitis, together with other sections on diet will help you to reduce the number of pathogenic bacteria that are signalling through the skin/gut pathway.

Rostaher, A., Morsy, Y., Favrot, C., Unterer, S., Schnyder, M., Scharl, M., & Fischer, N. M. (2022). Comparison of the Gut Microbiome between Atopic and Healthy Dogs—Preliminary Data. Animals, 12(18), 2377.

Masuoka, H., Shimada, K., Kiyosue-Yasuda, T., Kiyosue, M., Oishi, Y., Kimura, S., ... & Hirayama, K. (2017). Transition of the intestinal microbiota of dogs with age. Bioscience of microbiota, food and health, 36(1), 27-31.

García, C., Rendueles, M., & Díaz, M. (2017). Microbial amensalism in Lactobacillus casei and Pseudomonas taetrolens mixed culture. Bioprocess and biosystems engineering, 40(7), 1111-1122.

Zeng, T., Yu, X., & Chen, Z. (2021). Applying artificial intelligence in the microbiome for gastrointestinal diseases: a review. Journal of Gastroenterology and Hepatology, 36(4), 832-840.

Castronovo, L. M., Vassallo, A., Mengoni, A., Miceli, E., Bogani, P., Firenzuoli, F., ... & Maggini, V. (2021). Medicinal plants and their bacterial microbiota: A review on antimicrobial compounds production for plant and human health. Pathogens, 10(2), 106.

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