We are what we eat but are microbes also indicative of where we’ve been?
Probiotic considerations for petfood
It’s no secret that bacteria have a bad rap. With constant marketing of hand gels, soaps, wipes and other personal antibacterial products, it’s not surprising that most of the non-scientific public fears bacteria. Of course some bacteria should be feared. Pathogenic bacteria cause disease and exposure to these is an unpleasant experience. However, maintenance of the proper microbes in the intestinal tract allows animals to gain nutrients from their food that they cannot absorb from their own digestion. In fact, with over 1 billion bacteria in our intestine, the bacteria out-number our own cells 10 to 1.
After birth, mammalian intestinal development is driven by exposure to commensal, or normal resident, bacteria. Epithelial cell development – the process of blood vessel formation (angiogenesis) – and immune cell development are initiated by exposure to bacterial intestinal residents. The “hygiene hypothesis” is a popular theory that states that the increased rate of allergies and asthma in modern society can be attributed to a decrease in exposure to bacteria in the environment. The theory is that exposure to bacteria in the environment gives the immune system a proper perspective on what to attack and what to ignore. If the immune system is not stimulated, then the body will attack. With the high rate of skin allergies in dogs, is this true for man’s best friend as well?
Bacteria present in dogs and humans are similar, which is not surprising given our similar predispositions for eating what is available at any given time. The cat’s microbiome is still being determined. The microbial community of any animal is a dynamic population. Just like any other population, territorial disputes happen and if a bacterial species is displaced from the environment, it will undoubtedly be replaced with another more suited to the available nutrients and will get along with neighboring bacteria.
The genetic profiling of the microbiome, or the population of microbes present in the intestine, has revealed that each individual has a unique population of microbes. There are many factors that determine this mix of microbes. A few common ones include:
Age and gender
Animals transition from a liquid to a solid diet when they are being weaned from their mothers. The bacteria required to metabolize an all-milk diet is different from those that can utilize more complex feed substrates. Again when the animal becomes an advanced age, nutritional requirements change because older animals are not as able to digest foodstuffs. Hormonal differences between male and female animals can also alter bacteria flora between genders.
We are what we eat but are microbes also indicative of where we’ve been? In some ways, they are. Family members tend to have similar bacteria species, but there are individual variations within the numbers of these species (Turnbaugh, 2009). Animals that are raised exclusively indoors have different bacteria present in their intestines than those raised with exposure to an outdoor environment (Mulder, 2009). Dogs that run outside frequently could have a different variety of bacteria present in their intestine than more sedentary indoor animals.
The bacterial population will shift to better use the increase in available substrate when in the overfed or obese state. In a 2009 study, Turnbaugh and colleagues showed that there are differences in bacterial populations between obese and lean humans. It has been known for some time that germ-free mice (those raised without exposure to bacteria) do not become overweight even when overfed. However, when bacteria from obese mice were transferred to germ-free mice, they did become obese. This indicates that an intestinal microbiome that is efficient at using food will make another animal more efficient and could lead to a change in body condition. In addition, the systemic inflammation resulting from the obese, and in some cases insulin resistant, state can alter how the metabolism of the animal works. This translates into a change in microbial population.
The amount of diet provided is important but the dietary constituents also have a direct effect on the bacterial population. Bacteria must thrive on what they are given or they will no longer be in the population. The gaseous side effects of excess fiber are well known. But the benefits of short chain fatty acid metabolism by both microbe and host that can result in prebiotic fermentation are positive benefits to the host.
In the lab, the growth curve of bacteria may be easily manipulated by changing the media provided for nutrition. Simple sugars are used quickly and when they are used up the bacteria dies. More complex prebiotic fibers may give the desired beneficial bacteria a prolonged growth curve. In the animal, this gives the desired commensal bacteria an advantage for survival. Products that contain specific prebiotics that target the probiotic are known as synbiotics such as Subactil™ MOS.
Infection and Immune Status
When young, the immune system is not primed to deal with infectious agents. Then when elderly, it undergoes a process called immunosenescence. This essentially means that our immune systems go to sleep and become less able to respond to threats. Exposure to invading pathogenic bacteria by itself can displace the resident bacteria in the intestine by the use of toxins that cause diarrhea as well as the resulting immune response. In addition, the chemotherapeutic agents used to treat bacterial infections in the body can also kill off the commensal inhabitants of the intestine. New, opportunistic bacteria can move in and cause further disruptions in the population when the resident flora is affected. Probiotics may be used therapeutically to replace the normal flora to stabilize this population.
Probiotics, which are live bacterial products, have become popular for their proposed benefits to humans. This popularity has now spread to our pets as well. There are many things to consider when deciding how to choose the bacterial species included in a supplement or pet food diet such as:
When fed, live bacteria elicit a different immune response than when they are dead. In a 2009 study, Van Baarlen and colleagues investigated the differences in immune response when a probiotic strain of Lactobacillus was fed to mice when the culture was live and harvested when actively growing (mid-log growth phase) vs. a killed preparation of the same bacteria. They found that while the live bacteria stimulated intestinal cell proliferation, the dead bacteria stimulated the immune system of the mouse causing an inflammatory response characterized by TNFα cytokine excretion.
Similar results were found in a study conducted by Kemin Nutrisurance with the probiotic Subactil™. When fed to mice, at live doses from 107 to 1010 the Bacillus organism did not elicit an inflammatory response but a killed dose of the bacteria increased circulating levels of pro-inflammatory cytokines.
With only one layer of cells between the microbial population in the intestine and the rest of the body, it is important to have a friendly relationship with our intestinal bacteria. When searching for that probiotic to maintain that relationship for your pet, there are multiple considerations to contemplate including the lifestyle of that animal and the nutritional challenges it faces.
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