17 Jan 2023
Zoë Gratwick
Job Title
Antimicrobial resistance (AMR) is already a clinical problem in equine practice1. Drawing on available information, steps can be taken to minimise its rate of development. Our actions can make significant contributions to this global and local issue.
When considering antimicrobial-resistant bacteria, we may think of the direct spread of pathogens (for example, the zoonotic spread of MRSA), but the spread of resistance genes themselves is also important.
These genes can be passed into different species of bacteria, meaning bacteria once sensitive to a specific antimicrobial become resistant. This adds to the pool of antimicrobial-resistant bacteria in animals, people and the environment.
Some of the most relevant antimicrobial-resistant pathogens in equine practice include MRSA, extended-spectrum beta-lactamase (ESBL)-producing bacteria and multidrug-resistant bacteria. ESBLs are enzymes that inactivate extended spectrum beta-lactam antimicrobials such as ceftiofur.
The exact definition of multidrug resistance is different for different bacterial species, but it tends to mean that bacteria are resistant to at least one drug in three or more antimicrobial classes.
Antimicrobial-resistant infections in horses are concerning for a variety of reasons relating to equine patient health and care (Figures 1 and 2).
Antimicrobial-resistant equine infections are also important in the context of human health, because of the following reasons:
Some isolates from animals can cause immediate clinical disease in people. Alternatively, they may colonise people without causing symptoms, then act opportunistically when a subsequent surgical procedure or trauma occurs. This puts those who are colonised at increased risk of antimicrobial-resistant infections and the consequences of this.
It is recognised that MRSA infection is around four times more likely to develop in people who carry it in their nose2. This is a particular concern for vets, with multiple studies demonstrating a higher prevalence of nasal carriage in these professionals compared with non-vets.
Zoonotic transmission or contamination of the environment with bacteria carrying genes encoding AMR could lead to an increase in morbidity and mortality for affected people. Furthermore, exposure to antimicrobials leads to an increase in carriage of bacteria carrying resistance genes, which have the potential to be transferred to other bacteria.
Every time we use antimicrobials, we contribute to this situation (author’s emphasis). This is of particular importance when it comes to multidrug resistance to antimicrobials that are critically important for human health. A direct positive impact has been demonstrated between decreased antimicrobial usage in food-producing animals and decreased AMR in human pathogens3.
Three key areas for focus exist when considering practical measures against AMR in equine practice:
By considering these and other ways to slow the rate of development of AMR in equine practice, we can work together to limit the effect of this challenge on our patients and those who care for them.
