Antibiotic Residues in the Food Chain

Written by Tonya Mukherjee and Edited by Josephine Chan

With the global population expected to reach 9 billion by 2050, the need for agricultural products is growing. To keep up with the growing need of agricultural products, the agricultural industry commonly utilizes antibiotics in livestock to allow the animals to better process cheaper feeds, as well as to keep them healthy. However, the overuse of antibiotics poses a global health risk to both the environment and humans. 

Antibiotics are a type of medicine that is used to slow the growth of and eliminate microorganisms such as bacteria. Antibiotics are used in the livestock and aquaculture industries for two main reasons. Firstly, antibiotics have been found to deliver higher levels of livestock nutrient uptake in comparison to low-quality feed [1]. Secondly, they are used to prevent bacterial infections [2]. However, there are concerns about antibiotic residue in livestock products, including an increasing number of antibiotic-resistant bacteria in livestock, crops, and even wild animals, potential allergic reactions, and disruption of human microbiota [1] [2]. 

Recent studies have found that both livestock and wild animals possess unique antibiotic-resistant genes (ARGs), leading scientists to speculate that ARGs are somehow dispersing from agricultural farms to their surrounding environments. For example, earthworms live in soils and promote the growth of plants through the cycling of nutrients. However, earthworms are also known to facilitate the transfer of bacteria between crops through exposure [2] [3]. Studies show that ARGs can indeed be transferred through earthworms; it has been found that earthworms exposed to ARGs in animal manure often possess the same ARGs within their guts because the worms consume them through the manure[2] [3]. This is likely due to the overuse of antibiotics in livestock creating more ARG residues in their waste. ARGs have also been found to disperse through storm run-off and sewage waste near farms and agricultural factories [4].

To determine its impact in humans, antibiotic residues can be measured in human urine. Several studies in countries such as China have found both human antibiotic (HA) and veterinarian antibiotic (VA) residues in many human participants. HAs are used to treat infections, so there was a strong association between medical antibiotic usage and urine HA residue. Furthermore, VAs are frequently used in livestock. Studies in China found that the increased consumption of animals and animal-derived foods corresponded with a larger amount of VA residues in participant urine samples [5] [6]. 

Globally, millions of infections are reported yearly and cannot be treated with simple single‐antibiotic regimens. Also, due to antibiotics and their effects on human microbiota, studies have indicated that the exposure can result in adverse effects, such as immune and metabolic diseases [6]. One way to prevent ARGs is to compost manure to remove antibiotic residues. A study found that earthworms exposed to composted manure possessed fewer ARGs in their guts compared to those exposed to regular manure [2]. Interestingly, studies in China found a negative correlation between participants’ water drinking habits and VA residues in their urine [6]. Seemingly, consuming more drinking water may dilute VA presence in the body, a potential means that can be further researched to see its effect of reducing the levels of antibiotic residues in the body. 

References

1. Aslam, N., Sahibzada, S.,Wynn, P. (2019) Hormones and antibiotics in animal production: should they be used? EH Graham Centre for Agricultural Innovation. 
2. Zhou, S., Zhu, D., Giles, M., Daniell, T., Neilson, R., Yang, X. (2020) Does reduced usage of antibiotics in livestock production mitigate the spread of antibiotic resistance in soil, earthworm guts, and the phyllosphere? Environment International. 136: 105359.  
3. Ding, J., Zhu, D., Hong, B., Wang, T. H., Li, G., Ma., B. Y., Tang, T. Y., Chen, L. Q. (2019) Long-term application of organic fertilization causes the accumulation of antibiotic resistome in earthworm gut microbiota. Environmental International. 124: 145-152. 
4. Jacobs, K., Wind, L., Krometis, L., Hession, C. W., Pruden, A. (2019) Fecal Indicator Bacteria and Antibiotic Resistance Genes in Storm Runoff from Dairy Manure and Compost-Amended Vegetable Plots. Journal of Environmental Quality. 48; 4: 1038-1046. 
5. Wang, H., Wang, B., Zhao, Q., Zhao, Y., N., Su, M., Tang, C., Jiang, Y., Zhou, Y., Chen, Y., Jiang, Q. (2015) Antibiotic Body Burden of Chinese School Children: A Multisite Biomonitoring based Study. Environmental Science and Technology. 48; 8: 5070-5079. 
6. Wang, H., Tang, C., Yang, J., Wang, N., Jiang, F., Xia, Q., He, G., Chen, Y., Jiang, Q. (2018) Predictors of urinary antibiotics in children of Shanghai and health risk assessment. Environment International. 121: 507-514.