Diagnosis of intestinal dysbiosis

Photo: Mary Swift/Adobe Stock

Dysbiosis, a condition in which the microbiome changes, can be difficult to diagnose. Jörg M. Steiner, DrMedVet, PhD, DACVIM (SAIM), DECVIM-CA, AGAF, “Dysbiosis in Small Animals – What Do We Know?” lecture, regents and the university’s distinguished professor of small animal internal medicine, Dr. Mark Morris chair of Texas A&M University’s Department of Clinical Sciences Small Animal Gastroenterology and Nutrition spoke about the gut microbiome and the diagnosis and treatment of gut dysbiosis.

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

• Antibiotic-sensitive diarrhea (ARD): Diarrhea improves with antibiotics such as metronidazole
• Tylosin-sensitive diarrhea (TRD): Steiner noted that it is unknown whether TRD is the same ARD 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 condition because the current tools used are not sophisticated enough to assess the gut microbiome.

“…we came up with the term ‘gut dysbiosis’ because it kind of sums up all of (these conditions) without knowing whether they’re actually all the same thing,” Steiner said during his lecture.

Clinical symptoms

“The clinical manifestations (of intestinal dysbiosis) are the same as other (gastrointestinal) (GI) diseases,” Steiner explained. These symptoms include chronic intermittent diarrhea and, if the condition persists, weight loss. Patients may also have additional clinical symptoms caused by the underlying cause of dysbiosis.

Diagnosis

So how is gut dysbiosis diagnosed? Historically, quantitative culture of duodenal fluid was and still is considered the gold standard for assessing the intestinal bacterial ecosystem, according to Steiner. But as Steiner explains, it is now clear that this method fails to provide a comprehensive picture of the gut microbiota.

In addition, duodenal juice collection often poses several challenges and, if collected successfully, the sample must be plated on various media and dilutions must be made to ensure comprehensive identification of the species, which is not efficient.¹

stool cultures

Performing a nonspecific stool culture has also been recommended. However, Steiner warned against this method. “A basic stool culture won’t mean anything to you because most bad bacteria can’t be easily cultured. And so…the first thing you get on the stool culture (results) is, let’s say 5 or 6 different species, and those might be beneficial bacteria. These could even be potentially pathogenic bacteria, but (the results) are unlikely to be your actual pathogenic bacteria,” Steiner emphasized.

For example, if a bacterial culture is done without specifically culturing it, he explained. Salmonellawill not be cultured because the microbiota of fecal matter is too complex and inaccessible to nonspecific culture.

Measuring serum cobalamin concentration

Steiner explained that many bacterial species use and consume cobalamin, making measurement of serum cobalamin concentration a better method for diagnosing gut dysbiosis. “The problem with cobalamin is… you can’t discern why cobalamin is low. Is it low because the ilium is damaged and you can no longer absorb cobalamin, or is it because bacteria steal the cobalamin? There is no way to distinguish this,” Steiner said.

“Cobalamin is very useful for other reasons because it’s very important to know what’s going on prognostically, but for diagnostic reasons it’s useful to identify small bowel disease, but it’s not as useful to identify small bowel dysbiosis,” he continued.

Dysbiosis index

According to Steiner, the GI Laboratory at Texas A&M has developed polymerase chain reaction (PCR) assays that evaluate fecal levels of 7 bacterial groups in addition to the total bacterial count. According to Steiner, these analyzes use a mathematical algorithm to report changes as a single numerical value called the dysbiosis index (DI). He explained that a negative DI indicates normobiosis, while a positive DI indicates dysbiosis.

Specifically, this index has been trained to identify dysbiosis due to chronic enteropathy in cats and dogs. Overall, the dysbiosis index is a significantly more effective diagnostic tool for identifying gut dysbiosis than current methods, according to Steiner.

Reference

1. SteinerJ. Dysbiosis in Small Animals—What Do We Know?. Presentation Location: 2024 New York Vet Show; 7-8 November 2024; New York, NY.