DISTRIBUTION OF ANTIBIOTIC RESISTANCE GENES IN THE ENVIRONMENT
Combining geology, surface geochemistry and microbiology
ARg linked to an AFM tip: Force spectroscopy can provide data for understanding the interactions at a bond level. (AFM: atomic force microscope)
Combining recent research across disciplines, we find evidence that minerals hold a high and unrecognized potential for enhancing the distribution of the ARg in the environment. Adsorption of ARg to minerals significantly increases the ARg’s lifetime and facilitates their distribution by sedimentary transport processes. In addition, minerals also serve as a) sites for horizontal gene transfer (HGT), b) platforms for microbial growth and, hence 3) act as hot spots for propagation of adsorbed ARg to other microbes. However, some minerals and ARg are bound more strongly than others and various bacteria have different affinities toward various minerals. Those variations in affinity are poorly quantified but vital for predicting the distribution of ARg in the environment.
Bacterial colony formation.
By Lisselotte Jauffred (NBI collaborator)
The spread of antibiotic resistance genes (ARg) is a worldwide health risk1 and is no longer only a clinical issue. Vast reservoirs of ARg are found in natural environments2–4 such as soils, sediments and oceans. The emergence and release of ARg to the environment is in particular caused by extended use of antibiotics in farming, e.g. where the genes dissipate from the manure.5
Once in the environment, the ARg are surprisingly rapidly propagated. It is well known that the ARg are distributed to neighbor bacteria through processes of both cell sharing or through horizontal gene transfer (HGT) where one species acquirer resistance from another.6,7 Most HGT responsible for the spread of ARg are assumed to be through direct microbe-microbe contact.
However, I think the outcome of non-contact transfer is grossly underestimated. In the HGT mechanism called “Transformation”, free ARg in suspension or adsorbed to a mineral can be picked up and incorporated into non-related organisms. Considering that free DNA only can survive for a few weeks in sea- and freshwater environments,8–10 any HGT from free DNA can rightly be assumed to be local, but if the DNA gets adsorbed to a mineral, it can survive for up to 2 million years (Meet our mastodon).11–14 If this also holds for ARg, then minerals offer a potent mechanism for distributing ARg through our environments my means of sedimentary processes.