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Dysbiosis, a condition in which the microbiome is altered, can be difficult to diagnose. In his lecture “Dysbiosis in Small Animals – What Do We Know,” Jörg M. Steiner, DrMedVet, PhD, DACVIM (SAIM), DECVIM-CA, AGAF, Regents and Distinguished Professor of Small Animal Internal Medicine and Holder of the Dr. Mark Morris Chair in Small Animal Gastroenterology and Nutrition in the Department of Small Clinical Sciences at Texas A&M University, spoke about the gut microbiome, and the diagnosis and treatment of intestinal dysbiosis.

Presented at the New York Vet Show 2024 in New York, New York, the session began with an explanation of what dysbiosis is.¹ Steiner explained that the umbrella term “gut dysbiosis” encompasses various intestinal conditions in cats and dogs:

• Antibiotic Responsive Diarrhea (ARS): Diarrhea improves with antibiotics like metronidazole
• Tylosin-sensitive diarrhea (TRD): Steiner noted that it is unclear whether TRD is the same DRA, because tylosin is an antibiotic that also has an immunomodulatory function. It is not known whether diarrhea improves because tylosin is an antibiotic or because it is an immunomodulator.
• Small intestinal bacterial overgrowth (SIBO): It is unclear whether SIBO is a real disease because the tools currently used are not sophisticated enough to assess the gut microbiome.

“…we just came up with the term ‘gut dysbiosis,’ because it sort of sums up all (these conditions) without knowing whether all of these things are, in fact, the same thing,” Steiner said during his conference.

Clinical signs

“The clinical signs (of gut dysbiosis) are like those of any other (gastrointestinal) (GI) disease,” Steiner explained. These signs include chronic intermittent diarrhea and, if the illness persists, weight loss. Patients may also experience additional clinical signs caused by the underlying cause of dysbiosis.

Diagnosis

So how is gut dysbiosis diagnosed? According to Steiner, historically, a quantitative culture of duodenal juice was and still is considered the gold standard for assessing the intestinal bacterial ecosystem. However, as Steiner explains, it is now accepted that this method fails to provide a complete picture of the gut microbiota.

Additionally, collection of duodenal juice often presents several challenges and, if collection is successful, the sample must be plated on various media and dilutions to achieve thorough species identification, which is simply not efficient.¹

Fecal cultures

Performing a nonspecific fecal culture was also recommended. However, Steiner warned against this method. “A basic fecal culture will do you absolutely no good, as most bad bacteria are not easy to culture. And so…what you get on the fecal culture (results) are the first, say, 5 or 6 different species, and those could be beneficial bacteria. It could even be potentially pathogenic bacteria, but (it is) unlikely (that the results are) true pathogenic bacteria,” Steiner emphasized.

He explained that if, for example, a bacterial culture is carried out without specific culture for Salmonellait will not be captured in culture because the fecal microbiota is very complex and inaccessible by non-specific culture.

Measurement of serum cobalamin concentration

Many bacterial species utilize and utilize cobalamin, making measuring serum cobalamin concentration a better method for diagnosing gut dysbiosis, Steiner explained. “The problem (with) cobalamin (is)… you can’t differentiate why cobalamin is low. Is it low because the ilium is damaged and you can no longer absorb the cobalamin, or is it because the bacteria are stealing the cobalamin? There’s no way to differentiate that,” Steiner said.

“Cobalamin is very useful for other reasons, because it’s very important to know prognostically what’s going on, but for diagnostic reasons it’s useful for identifying small intestinal disease, but it doesn’t “is not very useful in identifying small intestinal dysbiosis,” he continued.

Dysbiosis Index

According to Steiner, Texas A&M’s GI Lab has developed polymerase chain reaction (PCR) tests that assess fecal levels of 7 bacterial groups in addition to total bacteria counts. These tests use a mathematical algorithm to report changes as a single numerical value, called the dysbiosis index (DI), according to Steiner. He explained that a negative DI suggests normobiosis, while a positive DI indicates dysbiosis.

More specifically, this index is trained to identify dysbiosis linked to chronic enteropathy in cats and dogs. Overall, the Dysbiosis Index is a significantly more effective diagnostic tool for identifying gut dysbiosis than existing methods, according to Steiner.

Reference

1. Steiner J. Dysbiosis in small animals: what do we know. Featured at: 2024 New York Vet Show; November 7 and 8, 2024; New York, New York.