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Dysbiosis and the Use of Pre‐, Pro‐ and Synbiotics

Jan S. Suchodolski, MedVet, Dr Med Vet, PhD, AGAF, DACVM

College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, USA

The Importance of the studies in humans and animals have associated intestinal
Gastrointestinal Microbiota dysbiosis, defined as alterations in intestinal microbiota
composition and/or richness, with various disorders
The intestinal microbiota is the collection of all live such as inflammatory bowel diseases (IBD), granuloma-
microorganisms (bacteria, fungi, protozoa, and viruses) tous colitis, obesity, diabetes mellitus, and allergies. For
that inhabit the gastrointestinal (GI) tract. The word these reasons, the normalization of dysbiosis appears to
microflora is often used in older textbooks, but microbi- be a prudent therapeutic goal.
ota (from bios, Greek: life) is the technically correct term.
The total microbial load in the intestine is estimated to
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represent between 10 and 10 organisms, which is The Gastrointestinal Microbiota
about 10 times the number of cells composing the host in Healthy Dogs and Cats
body. Because the majority of intestinal bacteria cannot
be cultured using commonly used plating techniques, We are just beginning to understand the complexity of
molecular tools (mostly targeting the 16S rRNA gene) are the microbiota and are only at a very early stage in our
now the standard for identification of microbiota, and abilities to properly assess the entire microbiota and its
have improved our understanding of the complex micro- functions. The microbiota varies along the GI tract, and
bial diversity in the intestine. It is estimated that the there are also clear differences between the mucosa‐
intestine harbors several hundred bacterial phylotypes. associated and luminal microbiota. Additionally, we are
The microbiota differs substantially on the species and not yet able to fully assess the interactions between the
strain level in each individual animal yet despite these dif- microbiota and the host immune system. Several recent
ferences, the metabolic end‐products in the intestine are studies have described which bacterial groups reside in
similar between individuals. This new insight into the the GI tract of dogs and cats, and some initial work has
complexity and individuality of the gastrointestinal been done to understand the metabolic interactions
microbiota has increased research efforts to better under- between microbiota and host.
stand the importance of a balanced microbial ecosystem Studies using traditional bacterial culture estimated
for regulation of host immunity in health and disease. that the bacterial load in the small intestine of healthy
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The interactions between intestinal bacteria and the dogs is typically 10 –10 cfu/g of small intestinal content,
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host immune system are mediated through various but can reach as high as 10 cfu/g. In the colon, the num-
mechanisms, either via direct contact between bacteria ber of cultivable bacteria is much higher, with up to
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and the innate immune system (e.g., via Toll‐like recep- 10 cfu/g. Molecular studies using high‐throughput
tors, NOD2 receptors), or through microbial‐derived sequencing are now the standard for microbiota charac-
metabolites. These metabolites can be either directly terization and have identified many novel and important
produced by bacteria (e.g., vitamins, short‐chain fatty bacterial genera that were previously not appreciated in
acids [SCFA]), or may be primary host metabolites that the canine and feline GI tract.
are converted through bacterial enzymes into secondary The predominant phyla in the feces of healthy dogs
metabolites (e.g., conversion of primary to secondary are Bacteroidetes, Firmicutes, Fusobacteria, and
bile acids, tryptophan into indole). Consequently, many Proteobacteria. Lower abundance phyla (less than 1% of

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical