How does AMR develop and how is it disseminated?
Antimicrobial resistance occurs when a microbe develops a mechanism to counteract the effect of a drug. There are four ways that this occurs: 1) Reducing the amount of drug that enters the cell; 2) Modifying receptors to essentially appear “invisible” to the drug; 3) Rendering the drug inactive; 4) Pumping the drug outside of the bacteria (NCBI, 2018). These mechanisms are developed through the evolution of bacteria as those with the most favourable characteristics to resist antibiotics survive and spread these adaptations through the population.
There are several ways by which these resistance mechanisms can then be spread to other bacteria. By overusing and oversaturating the environment with antibiotics we are contributing to the pressured and rapid evolution of bacteria. In other words, if one microbe develops a mechanism to resist the antimicrobial drug, it can survive exposure to the drug and pass on its adaptation, creating a stronger, more resistant microbial population. Another way for the resistance to spread is through a process called Horizontal Gene Transfer. This is a method by which bacteria can share their traits via genes to a neighbouring bacterium (not a direct descendant). Effectively, one bacterium could give its resistance traits directly to its neighbour (ScienceDirect, 2013).
Often times we assume resistance is spread only when antibiotics are present and give bacteria with resistance genes an advantage over non-resistant bacteria; however researchers have found that resistance genes continue to spread among bacteria populations even in the absence of antibiotics (Bakkeren, et al., 2019). Resistant bacteria known as “persisters” reduce their metabolism and fall into a dormant state in the presence of antibiotics in order to outlast the treatment. These bacteria can remain dormant for months and reawaken to cause the infection to flare up once again and spread resistance genes to other bacteria even long after antibiotics have left the environment.
Dissemination pathways for resistant bacteria:
- Human to human contact
- Direct contact with animals
- Processing, transport, or handling of food animals and food
- The environment (e.g. contamination of water and soil via manure or waste water discharge from plants manufacturing antibiotics)