Page 676 - Veterinary Immunology, 10th Edition

VetBooks.ir Dysbiosis

It is clear from the above discussion that the gut microbiota exerts a
significant influence on the systemic immune response. If this

microbiota becomes unstable or imbalanced, dysbiosis occurs.
Dysbiosis is a cause of equine laminitis and ruminal acidosis, and
has been implicated in the development of several immune-
mediated diseases such as canine chronic enteropathy and
inflammatory bowel diseases. Antibiotic treatment is an important

cause of dysbiosis. This can radically alter the composition of the
intestinal microbiota and increase the risk of developing infections
with organisms such as Clostridium difficile or overgrowth with

other unwanted pathogens. Antibiotics alter the composition of the
microbiota resulting in an increased risk of obesity. (Obese
individuals have more Firmicutes and fewer Bacteroides than lean
ones.) However, much remains to be learned about this very
complex subject. Perhaps the most significant dysbiosis is that

which leads to the development of allergies.
The role of the intestinal microbiota also extends to inflammatory
diseases. For example, antibiotic-induced intestinal dysbiosis in

mice affected circulating cytokine levels as well as the severity of
ischemia/reperfusion injury on the heart. Oral vancomycin
decreased circulating leptin levels, resulted in smaller myocardial
infarcts, and improved functional recovery as compared to
untreated controls. Modification of the gut microbiota by the

probiotic Lactobacillus plantarum had a similar effect. Even oral
antifungal drugs can disrupt the intestinal fungal microbiota in
mice and increase the severity of airway allergic disease.

In critically ill animals, breakdown of the intestinal epithelium
and mucosal barriers may permit leakage of bacterial components
into the body. Conversely, depletion of the gut microbiota,
especially as a result of antibiotic treatment, can make the mucosal
defenses vulnerable and perhaps reduce the priming of the

systemic immune responses. It may therefore be advantageous to
modulate the composition of the gut microbiota in some critically ill
animals by the judicious use of probiotics (Box 21.2).

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