6 Introduction of new resistance combinations from environmental reservoirs

There is an enormous diversity of bacteria in the environment. Mechanisms to resist environmental bacteriocides (compounds naturally produced by microorganisms to give them a competitive advantage) were already present in bacteria long before humans evolved. Therefore, environmental bacteria represent a reservoir for mechanisms of antibiotic resistance (Martínez, 2008). Environmental bacteria can possess genes that encode resistance to antibiotics on their chromosomes. Because most bacteria are not pathogenic, this does not in itself represent a direct risk to humans; however, through horizontal gene transfer – see the course Introducing antimicrobial resistance [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] for more details – these resistance mechanisms can be transferred between different bacterial species, including into animal and/or human pathogens.

This process is much more frequent if the resistance mechanisms are located within a mobile genetic element (also explored in detail in Introducing antimicrobial resistance). A single animal or human carrying a resistant bacterium or ARG can rapidly spread the resistance within their own environmental compartment.

Understanding the processes and pathways of AMR in the environment highlights the critical need for environmental AMR surveillance to monitor, detect and mitigate emerging resistance. In the next section you’ll take a close look at environmental AMR surveillance.