Research Roundup 13 - Good Bacteria

Good Bacteria, Your Pet and You

 Nancy Scanlan, DVM

There are so many bacteria in your intestine that their genes outnumber yours, 100 to 1. The beneficial bacteria in healthy human intestines are similar in type and proportions to the beneficial bacteria in dog and cat intestines. So studies in dogs (and the few that have been done in cats) can help us understand benefits and problems in humans. But even more important, to my way of thinking, all the human studies can give us insight into the best way to keep dog intestines healthy, too.

 Researchers have found 4 main families of bacteria in the gut: Firmicutes (with both the good Lactobacillus acidophilus bacteria, as well as the botulism bacteria), Bacteroidetes (Firmicutes:Bacteroidetes ratio is important in human disease), Proteobacteria (E. coli, both good strains and bad strains, are in this family) and Actinobacteria (with Bifidobacterium bifidus, found in yogurt and the large intestine, as one family member). Abnormal numbers (increased or decreased) and abnormal ratios with each other can cause or influence problems including obesity, allergies, kidney disease, chronic diarrhea, type II diabetes, autoimmune disease, IBD, fatty liver, digestive problems including malnutrition, and intestinal cancer.

 Studies have shown that the normal types and numbers of bacteria in each family are drastically changed in any animal with chronic diarrhea. This is influenced by inheritance: for example, Boxer dogs have a natural mutation that keeps them from being able to fight off certain diarrhea-causing germs. But even in a normal dog, the longer they have diarrhea, the more the pattern changes, causing damage to intestinal cells, a decrease in healthy bacteria, and an increase in unhealthy bacteria. For humans, there is a test to measure the ratio between 2 different species of bacteria which can keep track of how well treatment is working for inflammatory bowel disease.

 In humans and rats, it has been shown that bacterial strains are different for obese subjects than for thin ones. This was one explanation of why in some identical twins, one is thin and one is obese. By adding one type of bacteria from an obese mouse to other bacteria from thin mice, scientists were able to cause obesity in formerly thin mice. The longer a pet is overweight, the more their intestinal bacteria change, and the harder it is for them to get thin and stay thin.


Once a bacterial population has changed, it is hard to change it back. Bacteria that were changed to a more healthy type for a month tended to rebound to their old unhealthy population soon after treatment was stopped, even if they had been changed for as long as 4 weeks. So any special diet that is meant to change the bacteria in the intestine needs to be looked at as a permanent new diet, not something to give up as soon as your dog or cat is better. The best way to change bacterial populations is to supplement with good bacteria, supply the prebiotics that will let the good bacteria multiply, and to modify the diet to also help beneficial bacteria. For humans, one benefit of this research has been to add prebiotics to infant formulas, to make their composition closer to human breast milk.

 Current research is looking at which prebiotics benefit the good bacteria, and at fecal transplants to restore normal bacteria when other methods fail. It turns out that different bacteria are benefitted by different prebiotics, and for the best effect you may need to mix them. They are finding that you might want to increase one primary bacteria type, but for best effects a secondary type may also need to be fed with a different prebiotic. For example inulin can increase Bifidobacteria. Bifidobacter populations are important in the prevention and treatment of a number of diseases. (For more examples of how food and probiotics can help restore normal bacteria, see the next Research Roundup.)

 (To see the references, and to see how large of a knife a dog can swallow, see our HOPE newsletter.)