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What are the main causes of antimicrobial resistance?

The rampant misuse and overuse of antimicrobials in human, animal, and plant health has exponentially accelerated growing resistance. On top of these factors, ongoing pollution of the environment is contributing to the widespread presence of antimicrobials and antimicrobial resistance genes in the population.

Every year millions of antibiotic prescriptions are written inappropriately (National Institute for Health and Care Excellence (NICE), 2015). Because of incorrect or lacking information, some doctors may end up prescribing antibiotics for infections already resistant to this treatment or even for viral infections which are in no way treated by antibiotics. In other cases, second- or third- line antibiotics that are reserved for last-resort scenarios may be prescribed in situations where the first line antibiotic would have been able to treat the infection.

Antimicrobials, particularly antibiotics, are a critical part of food security which has made agriculture and aquaculture breeding grounds for resistance via improper usage. Antibiotics are used to treat infections in animals and plants; however, a more worrying usage is the practice of using antimicrobials to compensate for poor hygiene conditions and/or to promote growth (AMR Review, 2016).

As more and more antibiotics are becoming ineffective against resistant infections, last-resort antibiotics may be used more frequently. When used in livestock, the risk of AMR increases as low-level consumption of antibiotics in the food chain has the consequent effect of reducing antibiotic efficacy in humans (Allen HK, 2014). Globally, it is not uncommon for more antimicrobials to be used on animals than for human health. In the U.S., for example, over 70% of antibiotics deemed medically important for humans are used in animal husbandry (The Review on Antimicrobial Resistance, 2015).

In the environment there are many so-called “hot-spots” where antimicrobial resistance is more likely to develop due to inappropriate and polluting disposal of antimicrobials. Studies have shown pronounced spikes in resistance around pharmaceutical manufacturing sites, aquaculture, and agriculture runoffs. In household environments, resistance is likely to emerge in areas where knowledge of proper antibiotic disposal is low, and people get rid of old or unused drugs through their toilets, sinks, or general household garbage. (Larsson DG, et al., 2007)  (J Hazard Mater, et al., 2017) (Berendonk, et al., 2015); (Bengtsson-Palme J, et al., 2014),  (Flach, et al., 2015) (Pruden A, Larsson DGJ, Amézquita A et al. (2013) (AMR Review, 2016) (Landers, 2012,)

For plant diseases, some antimicrobials such as streptomycin, kasugamycin, oxytetracycline, and oxolinic acid are important for treatment and control. However, the use of these antimicrobials contaminates the soil which contributes to the development of antimicrobial-resistant bacteria and antimicrobial resistance genes (Stockwell and Duffy, 2012) (Sundin and Wang, 2018)