The human microbiome corresponds to all microorganisms that have colonized the human body and inhabit organs such as the skin, mouth, nose, digestive tract or vagina. The intestinal microbiome is the largest microbiome in the human body, both in terms of weight and composition, and refers to the dense population of bacteria in the gastro-intestinal tract and particularly the colon.
The key role of a healthy intestinal microbiome is everyday more and more ascertained. It contributes to many aspects of human health via the metabolic activities of the several hundred species of which it is composed. Acting as a barrier against many harmful bacteria, a healthy and diverse microbiome plays a crucial role in prevention of life-threatening infections. It also contributes to the digestion of certain foods, the regulation of host metabolism, and increasingly appears as a precious ally to ensure optimal activity of the immune system.
When we take antibiotics orally, part of the dose is not absorbed and reaches the gastro-intestinal tract; similarly, a part of the antibiotic dose taken by injection is recycled through the liver, and excreted into the intestine with the bile. When those antibiotic residues reach the colon, they provoke a serious disruption of the intestinal microbiome: several bacterial populations are decimated whereas others (sometimes pathogenic and resistant to antibiotics) proliferate; this state is called dysbiosis. The intestinal microbiome balance is hence disturbed and may take weeks to months to fully recover, i.e. return to its original equilibrium. Other drugs are also known to disrupt the microbiome such as some anti-cancer chemotherapies.
Similarly to a damaged organ, a disrupted microbiome can no longer fulfil its physiological functions, leading to many adverse consequences including: