There is a growing danger as big as, but lesser known than, the looming threat of climate change: antimicrobial resistance (AMR). Defined by the Food and Agricultural Organisation of the United Nations (FAO) as “micro-organisms—bacteria, fungi, viruses, and parasites—[evolving] resistance to antimicrobial substances, like antibiotics”, AMR adversely affects food safety and security by rendering medicines much less effective or useless when it comes to treating infections. While it is difficult to quantify the full economic and health impact of AMR, the FAO estimates that global GDP will decrease by 2 to 3.5%, equivalent to USD100 trillion, by 2050, with up to 10 million human lives lost each year.
Generally, antimicrobials in agriculture are used by farmers in the livestock production and fish farming industries to treat sick animals, to prevent future disease from spreading amongst livestock, and to stimulate growth, usually via the feed and water provided to the animals. In plant agriculture, antibiotics are usually sprayed onto plants as a fine mist, although direct antibiotic application on crops is much more modest compared to its use in livestock (McManus et al., 2002); however, it should be kept in mind that indirect applications could still happen via the use of manure and wastewater already contaminated (Zhang et al., 2017).
The amount of animal consumption of antibiotics is rather eye-opening—in the United States throughout 2012 alone, 72.5% of the use of medically important antibiotics were found to have been for animals, with only 27.5% used by humans; in absolute figures, animal consumption of antibiotics was 8.9 million kg compared to human consumption of 3.4 million kg (FDA, 2012; IMS Health, 2012).
“When we have a flock and there’s a lot of sick chickens in that flock, the quickest way to get an antibiotic in them is to put it in the water. We do that through a system that proportions that water out uniformly through all of these water lines so that every drink, every drop has the correct amount of antibiotics.”
The same practices were later adopted in aquaculture, the difference being that antibiotic doses may be proportionally higher than doses in livestock (O’Neill, 2015). Residue from antimicrobials as well as undigested food and faeces containing unabsobed antimicrobials usually remain in the water and the surrounding sediments for an extended amount of time, with some studies further suggesting that 70 to 80% of antibiotics administered to fish are excreted into the water (Cabello et al., 2013; Burridge et al., 2010).
Pathways of AMR genes from closed and open aquaculture systems into the water and its surrounding environment (Watts et al., 2017).
In comparison, the antibiotic use for crops is relatively low, comprising only 0.36% of total agricultural antibiotic consumption (Smalla and Tiedje, 2014). While this resulted in much less attention given to antibiotic use in plants, the potentially extensive use of fungicide may be a source of concern since fungal diseases presents significant threat to crops (O’Neill, 2015).
It is quite undeniable that the issue of AMR is an increasingly alarming one. With news of bacteria developing new resistance to antibiotics and increasing resistance in animals such as dolphins, it is clear that, quoting author and journalist Maryn McKenna in her book Big Chicken, AMR is becoming “an overwhelming threat, created over decades by millions of individual decisions and reinforced by the actions of industries.” It would be interesting to see further developments in this area.
This is the first article of a multi-part series on the topic of antimicrobial use in the agri-food sector by Khor Reports.