AMR is the ability of microbes (such as bacteria, viruses, fungi) to counteract the effectiveness of antimicrobial drugs (such as antibiotics, antivirals, antifungals) against them. Even when antimicrobials are used appropriately, microbes can develop resistance. However, the development of resistance is accelerated by their misuse and overuse in human, animal, and plant health along with the pollution of the environment with antimicrobials and antimicrobial resistance genes.
Drug-resistant infections already claim at least 700,000 lives a year, including 230,000 deaths from drug-resistant tuberculosis (WHO, 2019). By 2050 resistant infections could kill 10 million people annually and lead to an economic slowdown comparable to the global financial crisis of 2008. As life-saving antibiotics stop being effective, AMR could end our capacity to combat infections.
Antibiotics in Animal Husbandry
Antibiotic usage in animals is an imperative factor contributing to the wider range of resistance, particularly with intensive animal production. The spread of resistant bacterial populations can be transmitted from animals to humans via direct contact between the two, or through the food chain and the environment. WHO recommends an overall reduction in antibiotics usage within food-producing animals to help preserve their effectiveness for human medicine (WHO, 2017).
Antimicrobials are critical for animal health, welfare, and food security when used to treat infections in agriculture and aquaculture. However, infection treatment is not always the leading reason for antimicrobial use; globally, antimicrobials are used most often to prevent infections, compensate for poor husbandry practices, and/or to promote growth (AMR Review, 2016; Landers et al., 2012). Although data on the exact amounts of antimicrobials used in global food production is deficient or completely absent in certain areas, the data we do have paints a serious picture. In the US for example, more than 70% of antibiotics considered to be medically critical for human health are used in livestock (AMR Review, 2015). Research predicts that this high level of antibiotics in agriculture will only increase without intervention; globally, consumption is expected to increase by 67% from 2010 to 2030 while consumption in BRICS countries (Brazil, Russia, India, China, and South Africa) specifically is predicted to rise by 99% over the same 20 years (Van Boeckel et al., 2015).
When an infection has not responded to other drugs, last resort antibiotics may come into play; the frequent use of these last resort drugs in livestock can rapidly increase the threat of AMR and impact our ability to continue to use them effectively in human medicine when they are routinely absorbed in low levels through the food chain. Colistin is used very sparingly in humans as it can cause kidney failure; however, when no other antibiotics have been effective, colistin is an important last resort (AMR Review, 2016). Widespread use of Colistin in animals has led to resistance in animal pathogens, which has concerning implications for human health. A recent study in China has shown the discovery of transferable colistin resistance in bacteria in both humans and animals (Yi-Yun Liu et al., 2016).
Animal husbandry presents a multitude of problematic antibiotic use practices ranging from growth promotion to both metaphylactic and prophylactic use. Metaphylactic use attempts to prevent infections spreading from sick animals to healthy ones. However, in practice this only aids in the development of antibiotic resistance by adding large, unnecessary quantities of antibiotics to animals and the environment. (AMR Review, 2015). Despite using antibiotics to attempt to reduce disease spread, it is often difficult to avoid due to cramped conditions which expounds the problem. Growth promotion is seen as the most egregious non-therapeutic use of antibiotics, as such the practice was banned in the EU in 2006 (REGULATION (EC) No 1831/2003); however, it is still allowed in the US and other countries around the world.
Animal-based products are not the only food sources that may be contaminated with antimicrobial resistant bacteria and/or antimicrobial resistance genes; ingredients added during food processing can also be vehicles for resistance spread. These ingredients can include starter cultures, probiotics, and bio-conserving microorganisms. When raw food is mixed with other ingredients cross contamination can occur and increase the likelihood that bacteria will spread. While cooking can often kill resistant bacteria, consumption of raw food products creates a substantial risk of transferring antimicrobial resistance to humans (Verraes et al., 2013).