OH-STAR, the One Health Selection and Transmission of Antimicrobial Resistance project

Without antimicrobial drugs, the risk of bacterial infection would render many common medical procedures too dangerous to contemplate because of the risk of infections caused by opportunistic bacteria. These bacteria can live on a patient's skin or in their intestines, causing infection when bacteria get into parts of the body that are normally sterile. A perfect example is urinary tract infection (UTI) which is most often caused by faecal bacteria.

E. coli is particularly abundant in human faeces so is perfectly placed to cause opportunistic infections. It is one of the most common causes of healthcare pneumonia, surgical site infection, bloodstream infection and UTI in the UK. In order to prevent and treat opportunistic infections, patients are often given antimicrobials. Almost all antimicrobials are antibiotics, derived from natural chemicals produced by microbes found in the environment.

Natural antibiotics have been present in the environment for millions of years, and so bacteria living in their presence have had time to evolve mechanisms that can resist their actions, encoded by resistance genes. Opportunistic bacteria like E. coli can randomly acquire these pre-evolved resistance genes and in a single step, they become insusceptible to a particular antimicrobial. If that insusceptible E. coli colonises a person and then causes an opportunistic infection, the infection will not be treatable with that particular antimicrobial. These antimicrobial resistant (AMR) bacteria don't just resist clinical antimicrobial therapy, they beat it.

Animals also carry an abundance of E. coli in their intestines and are frequently treated with antibiotics. This can select for AMR E. coli which can then be passed on to other animals either directly or via contamination of the environment with faeces. Theoretically, the AMR E. coli could also be passed on to people, and there is much debate about whether such zoonotic transmission happens to any significant degree.

This is an important question because it has led to calls from some to dramatically reduce the amount of antimicrobials that are given to animals with the view that it will reduce the level of AMR in animals, and so the possibility of zoonotic transmission to people. But the potential impact on welfare and food production means this should only be done if there is evidence that it will work.