Feline gut microbiome 101

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The feline gut microbiome, a collective term that refers to the communities of microorganisms residing in the gastrointestinal tract of cats, has become an area of growing interest and research in veterinary medicine. Felines possess several unique gastrointestinal traits distinct from other companion animals. Cats are obligate carnivores and their taste buds are responsive to amino acids, but not sugars.¹ They have a shorter digestive tract relative to their body length and lower food retention time than dogs, as well as a less-developed cecum.² The pH of a cat’s stomach is highly acidic, ranging from 1 to 2, which is important for the breakdown of proteins and the eradication of pathogens.³ Cats also possess higher levels of proteolytic enzymes, such as pepsin, which optimize protein metabolism.⁴ They are notably deficient in amylase, rendering carbohydrate digestion less efficient when compared with canines and other animals with higher amylase activity.5 However, multiple studies have shown that cats are capable of digesting properly processed carbohydrates with over 90% digestibility.^4-7 Further research into the ability of a cat to metabolize different macronutrient compositions has shown that cats, like other mammals, can adapt their nutrient metabolism in response to dietary changes.^8-12

Although they are obligate carnivores, cats still possess a rich gastrointestinal (GI) microbiome capable of fermenting nutrients, such as carbohydrates, in their hindgut. This article will explore the role of some of the different bacterial species of the cat GI microbiome and their role in feline health and disease.

Composition of a Healthy Microbiome

A healthy feline gut microbiome is diverse and balanced. Key bacterial phyla include Firmicutes (36% to 50%), Bacteroidetes (24% to 36%), Actinobacteria (4% to 7%), and Proteobacteria (11% to 12%).¹³ The abundance and function of each of these phyla are influenced by multiple factors, including age, breed, diet, living environment, and other environmental exposures.¹⁴ Below are some specific genera and their functions within the feline gastrointestinal tract:¹³

Firmicutes:

• Lactobacillus: These bacteria are known for their role in fermenting lactose to produce lactic acid, thus helping to lower the pH of the gut, which inhibits harmful bacteria. They also contribute to the overall health of the intestinal lining and support the immune system.
• Clostridium: This genus includes both beneficial and pathogenic species. Beneficial Clostridium species help in fermenting complex carbohydrates and producing short-chain fatty acids (SCFAs), like butyrate, which are crucial for colon health.

Bacteroidetes:

• Bacteroides: Bacteroides species are efficient at breaking down complex molecules like polysaccharides. They produce SCFAs, primarily propionate and acetate, which serve as energy sources for colonocytes and have anti-inflammatory properties.
• Prevotella: Known for their role in carbohydrate metabolism, Prevotella species help break down dietary fibers as well as produce SCFAs.

Actinobacteria:

• Bifidobacterium: These bacteria are essential for the fermentation of dietary fibers, leading to the production of SCFAs like acetate. They also play a pivotal role in modulating the immune system and preventing the colonization of pathogenic bacteria.

Proteobacteria:

• Escherichia (E coli): While often associated with pathogenic strains, nonpathogenic E coli strains are part of the normal gut flora and contribute to vitamin K synthesis and the competitive exclusion of harmful bacteria.

Verrucomicrobia:

• Akkermansia muciniphila: This species degrades mucin, playing a significant role in maintaining the gut barrier and immune modulation.

Role in Feline Diseases

The balance of these bacterial populations is crucial for maintaining gut health. Dysbiosis, or the imbalance of gut microbiota, is linked with various diseases in cats, including:

Chronic inflammatory enteropathies (CIE):

• CIE is a chronic inflammatory condition characterized by persistent GI symptoms. Studies show that cats with CIE often exhibit a reduced diversity of gut microbiota, particularly a decrease in beneficial firmicutes, lactobacilli and bifidobacteria, and an increase in pathogenic genera staphylococci spp, streptococci spp, Escherichia spp, Critobacter spp, Klebsiella spp, Proteus spp, Pseudomonas spp microorganisms, as well as the fungi Candida.¹⁵ The altered microbial composition can contribute to chronic inflammation, diarrhea, and malabsorption.

Diarrhea:

• Acute and chronic diarrhea in cats has been linked to dysbiosis. The overgrowth of opportunistic pathogens like E coli and Clostridium perfringens and a decrease in beneficial bacteria is commonly seen.

Chronic kidney disease (CKD):

• Cats with CKD had a significantly decreased fecal microbial richness and diversity as well as increased uremic toxin production.¹⁶ These disturbances further worsen renal dysfunction and increase systemic inflammation.

Obesity:

• Like in other species, the gut microbiota in obese cats tends to differ from their lean counterparts. Obese cats have a significant reduction in microbial diversity as well as a decreased ratio of firmicutes to bacteroidetes. Pathways related to fatty acid synthesis are significantly more prevalent in the microbiomes of obese cats compared to those of normal-weight cats, which may influence nutrient absorption and fat storage.¹⁷

The GI microbiome of cats, primarily consisting of firmicutes, bacteroidetes, proteobacteria, and actinobacteria, plays a vital role in health and disease. Understanding these microbial populations holds significant promise for treating various feline diseases, particularly those involving chronic GI inflammation and metabolic disorders.

Intended for Veterinary Professionals

References

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