We have tiny visitors that have taken advantage of their evolutionary squatting rights throughout our bodies; these microbes make up our microbiome. Nobel Laureate Joshua Lederberg best defined the human microbiome as “the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space”.
This means we have 3 distinct types of microorganisms sharing our bodies with us:
1) The Commensals: Commensalism is relationship between two organisms where one benefits without affecting the other, derived from the English work commensal meaning “eating at the same table”.
2) The Symbionts: This is a clear mutualistic relationship, both parties are benefiting, both parties are happiest. We provide love to our microbiome, they provide love back to us (and by love I mean nutrients and protection from harm).
3) The Pathogens: These are the microbes that cause disease. The main distinguishing factor of a pathogen vs. a commensal is that a pathogen causes harm to the host.
Maintaining the perfect balance of all 3 of these microbe-types is essential for the equilibrium of the microbiome. An altered microbiome has been linked to depression, obesity, diabetes, anxiety, autism, cancer, rheumatoid arthritis, muscular dystrophy, multiple sclerosis, fibromyalgia and many other negative aspects of being human that we have yet to link.
We know one sure-fire way to disrupt the gut microbiome is to treat a human with oral antibiotics. Yes, the cure for most bacterial infection is to wipe out your entire ecological masterpiece you’ve worked on for decades in your gut.
Essentially, your commensals and symbionts work together to protect you from the potential harm that can be caused by the pathogens. We don’t understand fully how the protection works, but we do know that the presence of commensals and symbionts are essential for keeping the pathogens at bay.
One hypothesis is that your commensals and symbionts are creating a literal barrier between you and the pathogens, and if you wipe out this barrier with antibiotics that is when the scary pathogens take over.
In fact, oral antibiotic use is one of the leading risk factors for the disease associated with Salmonella ssp. and Clostridium difficile (C diff).
In most cases, Salmonella spp. causes salmonellosis (or food poisoning) and typhoid fever, whereas C. difficile causes antibiotic-associated diarrhea (AAD). In more severe cases Salmonella spp. can cause sepsis and C. difficile can cause “pseudomembranous colitis”, a severe inflammation of the colon.
But back to our story! The key is to keep these pathogens quiet and happy, and if oral treatment with antibiotics disrupts the microbiome barrier that leads to these pathogens causing disease and harm…
What is it about the disruption of the microbiome by antibiotics that benefits the proliferation of the pathogens?
Turns out, sugar availability is at an all-time high for these pathogens when the microbiome is disturbed, specifically an increase in sialic acid (yum!) and fucose (yummier!).
The mammalian host is nutrient diverse and rich, allowing for microbial populations to snuggle up and settle in – however the intestinal microbial community (or the microbiota) is composed of trillions of bacterial cells, making nutrient availability a little more stringent for those invaders that try to squat in the gut.
Alteration of the microbiome leads to an alteration of the carbohydrate availability in your gut – and the pathogens that are now rattled by the disruption of the microbiome now have unlimited food.