Long before humans started to mass-produce antibiotics to prevent and treat human infectious diseases, bacteria were evolving the ability to tolerate them. Antimicrobial resistance (AMR) is a global health challenge. Pathogens acquire new resistance factors from other species, and thus this reduces our ability to prevent and treat bacterial infections.
Antibiotic resistance can come from mutations in a genome of a bacterium and from uptake of foreign DNA. All antibiotic classes (natural, semi-synthetic, or synthetic) have been met by resistance. The horizontal transfer of a large range of antibiotic resistance genes (ARGs) to many bacterial species, particularly to those causing disease. The first step is the ARG movement within the genome. Secondly, there is a relocation of the gene to an element that can move between cells, third step is horizontal transfer of a resistance gene, and the fourth step is the physical transfer of the bacterium carrying the ARG to the human or domestic animal microbiota, a term called ‘ecological connectivity’. For the majority of ARG’s, their origin is not known, possibly because they originate from environmental species that have not yet been sequenced.
Antibiotics find their way into the environment via excretions from humans/animals, via improper disposal, from direct environmental contamination and via waste streams from antibiotic production. The introduction of antibiotics as clinical agents changed the preconditions for the evolution and spread of resistance by providing selection pressures, especially on members of the microbiota of humans and domestic animals, but also in environments heavily polluted with antibiotics.
Are we beginning to understand the connections between the human, animal and environmental microbiota? One Heath is defined as defined as a ‘collaborative, transdisciplinary approach at the local, regional, national, and global levels with the goal of achieving optimal health outcomes recognizing the interconnection between people, animals, plants, and their shared environment.’ Global efforts are underway to understand AMR and the impacts it can have on future generations to come.
Reference
Larsson, D.G.J., Flach, CF. Antibiotic resistance in the environment. Nat Rev Microbiol 20, 257–269 (2022). Link.