The Gut Flora is a Reservoir of Resistance Bacteria
The Human Intestinal Flora
The human intestinal tract is naturally colonized by a huge bacterial population. The gut contains 10 times more bacteria than there are cells in our body, i.e. 100 trillion bacteria! This microbial population, called intestinal flora or microbiota, contains more than a thousand known bacterial strains. The microbiome (the sum of all the genes coming from the bacterial population within a defined environment) of the gut microbiota can be considered as our "second" genome. It contains indeed more than 3.3 million genes: 150 times more than the number of genes in the human genome!
Understanding the relationship between the gut microbiota and human health is of utmost importance since our health appears to be highly dependent upon the balance within this ecosystem. Indeed, we know that the intestinal flora contributes to the digestion of certain foods, acts on the immune system and is a barrier against certain harmful bacteria.
Intestinal Bacteria May be Reservoir for Resistance
Antibiotics have a huge impact on the gut microbiota balance. When an antibiotic is administered, whether through an oral, intramuscular or intravenous route, a variable part of the dose is not absorbed into the blood but ends up in the intestinal tract. The unabsorbed fraction crosses the ileo-caecal valve and finally reaches the caecum, at the beginning of the large intestine or colon. In the colon, home of the densely population commensal flora, antibiotic residues kill a high number of (beneficial) bacteria, exert a selective pressure and participate to the selection of resistant strains. They interfere heavily with commensal bacteria’s metabolism and disrupt locally the homeostasis of the flora. This phenomenon is particularly strong in the caecum, a region populated by a particularly prolific bacterial population due to a high concentration of nutrients. Locally, the antibiotic residues increase the selective pressure and push the resistant bacteria to thrive and the susceptible ones to die off.
You may find an illustration of this phenomenon in the first part of the DAV132 video.
As a consequence, antibiotics provoke colossal side-effects in the intestinal flora: drastically altering the population equilibrium and selecting for antibiotic resistant traits. Antibiotic resistance is amplified in the colon which becomes a reservoir of resistance: resistance genes and bacteria can spread from the colon and contaminate the environment.
Learn more on the global spread of resistance!