Effects+of+Agriculture+on+Antimicrobial+Resistance

toc = Introduction =

Ever since their inception, antimicrobials ([|antibiotics]) have been a staple for public health and healthcare worldwide. Lowering global mortality rates significantly and allowing complex therapies and procedures to occur. Resistance to these antimicrobials (AMR) is a naturally occurring phenomenon resulting from selective pressures, but as a result of inappropriate and overuse of these miracle drugs, AMR has spread at an alarming rate and has become one of the biggest threats to public health today. By the year 2050, an estimated 10 million people will die annually as a result of antibiotic-resistant infections ([|Review On Antimicrobial Resistance], 2016).

One factor that significantly contributes to the spread of AMR that is often overlooked is the agriculture sector and the use of antibiotics in food animal production. Antibiotics are commonly used for livestock and food benefits, but recent evidence suggests a relationship between the number of antibiotics used on animals and a rise in human AMR. The transfer of AMR via bacteria includes environmental and commensal microbes as well as foodborne pathogens.

**Antibiotic Use In Livestock**
Whether used to combat common livestock bacterial diseases nonspecifically or to promote growth, antibiotic use in livestock is abundant. While its direct impacts on the animals is positive, it largely contributes to AMR The over and misuse of antibiotics in farm animals has led to an increase of AMR bacteria in animal habitats (Review On Antimicrobial Resistance, 2016; Bartlett, Gilbert, and Spellberg 2013; Holmberg et al. 2010). These AMR reservoirs can be easily spread to humans through several direct or indirect methods (Economou and Gousia 2015).

While there are gaps in global data, about 80% of antibiotics sold in the U.S. are used for livestock (Bartlett, Gilbert, and Spellberg 2013). Often when just a select few animals in the flock develop an infection, the entire flock is treated with antibiotics, a process known as metaphylaxis. In China, the world’s leader in antibiotic consumption(210 million kg per year), 46% of antibiotic use is in livestock (Pruden et al. 2013).

Currently, all major classes of antibiotics that are used in clinical settings are used in food animal production (Silbergeld, Graham, and Price 2008). Some common antibiotics used are [|tetracycline], [|erythromycin], [|penicillin], [|amoxicillin], and 2nd-4th generation [|cephalosporins.] Some of the antibiotics being used are last-line antibiotics used to treat humans with resistant infections. While not every antibiotic used on animals is used for humans, these are still very similar to those that are, often containing many identical features (Thanner, Drissner, and Walsh 2016). Additionally, antibiotics that have yet to be approved for human clinical use are commonly permitted for animal consumption and thus the effectiveness of new clinical drugs upon clinical registration has been shown to be diminishing (Silbergeld, Graham, and Price 2008).

**Antibiotic use in Plant Agriculture**
Springtime antibiotic sprays are essential for the control of plant-based bacterial diseases, namely bacterial spot of peach and fire blight in orchard trees. While the amount of antibiotic used in plant agriculture is minimal compared to animal farming (about 0.12%) it is still worth noting. Because the antibiotics are only active for a few days or weeks, no significant antibiotic residues were found on fruits that were harvested, so little AMR is spread through consumption of plants (Stockwell and Duffy 2012). However, spray antibiotics can get into the soil creating AMR bacteria that have the potential to spread to water systems (Thanner, Drissner, and Walsh 2016). When exposed to antibiotics, most of their bacteria will die, but a few will survive as a result of random mutations. These resistant bacteria will then transfer their genetic material to other bacteria and proliferate making a reservoir of AMR genes. As AMR bacteria develop and grow within the animals, resistance is transmitted to humans both directly and indirectly through food, animal waste, plants, soil, water, and direct contact(Bartlett, Gilbert, and Spellberg 2013).

**AMR Transfer Through Food**
//[|Enterobacteriaceae],// which includes //E.coli//, //Salmonella, Yersinia pestis,// and //Klebsiella//, is a large family of bacteria that is abundant in the guts of mammals and is the most common foodborne pathogen. When exposed to antibiotics, some of these bacteria become resistant(Holmberg et al. 2010). As the meat carcass is handled and processed, the bacteria from the gut may contaminate the meats or surfaces that the meats touch (Hayes et al. 2004). In middle Tennessee, of the 249 meat samples taken, 95.2% of them contained //Enterobacteriaceae,// and of those bacteria, AMR to erythromycin, penicillin, ampicillin, streptomycin were seen in 100, 89, 65.8, and 43.8% of the samples respectively with many bacteria exhibiting multi-drug resistance (MDR) (Kilonzo-Nthenge, Rotich, and Nahashon 2013). If these meats are cooked properly, the pathogens will be killed but this is occasionally not the case. Additionally, meat cartons can leak, raw meat can contact utensils and common household surfaces all of which can then transfer the AMR pathogen to humans.

**Animal Waste**
Stool excreted from an animal contains an incredible number of bacteria from their gut. As previously mentioned, it is possible for food animals to develop AMR bacteria within their gut. If this occurs, the resistant bacteria will be excreted with the waste as manure. Additionally, upwards of 90% of antibiotics administered to animals are excreted via urine or stool (Bartlett, Gilbert, and Spellberg 2013). These excreted antibiotics, and resistant bacteria are then dispersed throughout microbial-rich environments that facilitate both the horizontal transfer of resistant genes from host bacteria to environmental bacteria and the development of new resistant species by exposure of environmental bacteria to antibiotics (Economou and Gousia 2015). Also, manure from farm animals is commonly used as a fertiliser, if it still contains resistant bacteria and antibiotics, it will be dispersed in the soil.

**Water**
One common way in which antibiotics and AMR bacteria get into water sources is surface water and runoff. Water with faecal matter from farming environments (food-producing units) leads to the natural dispersal into the environment (Review On Antimicrobial Resistance, 2016). Wastewater from farming communities is rich with AMR bacteria and is the principal source for release of AMR bacteria and genes into the environment via irrigation and water supply (Baquero, Martínez, and Cantón 2008). Agriculture is a sector that needs and uses extraordinary amounts of water, the water used on plants will reach the soil where AMR bacteria likely resides and can then be transferred into groundwater sources and distributed to humans(Wellington et al. 2013).

**Plants and Soil**
On the planet, there are approximately 5x10^30 bacteria (mostly non-pathogenic), one gram of soil contains anywhere from 10^7-10^9 bacteria comprised of thousands of species (Wright 2010). Soils near farming communities and soils used for plant agriculture commonly include animal waste in the form of fertiliser and slurry (Wellington et al. 2013). When exposed to soil with such a high density of bacteria, transfer of resistant genes is inevitable. Although many of the bacteria in the ground are non-pathogenic, the majority of resistant factors seen in clinical settings have been recruited from these bacteria (Pruden et al. 2013). Additionally, it has been observed for soil to hold antibiotics and AMR gene carrying integrons particularly well allowing them to be preserved upwards of 10 months within natural and aqueous environments, exposing them to diverse bacteria (Baquero, Martínez, and Cantón 2008; Byrne-Bailey et al. 2011).

**AMR Transfer Through Direct Contact**
People who have direct contact with animals can also acquire AMR within their bacterial flora. Unsanitary conditions, contact with animal waste, and inhalation of dust containing bacteria provides the means of spreading. While this may not appear to be a serious threat, these people can then spread AMR to health communities and other people within their community through traditional human to human transmission. Numerous studies show that slaughterhouse and Farmworkers, veterinarians, people around food producing animals are at risk and have shown higher cases of AMR (Marshall and Levy 2011). In Maryland and Virginia, poultry workers had 32 times greater chances of carrying an antibiotic resistant strand of //E. coli// than people in the community (Price et al. 2007).

=**Conclusion**=

Due to its increasing threat to human health, the scientific community has recently performed a substantial amount of research on AMR including its many causes and strategies to combat it. From this, a relationship between the spread of AMR and agriculture has been established. We have determined just how prevalent antibiotic use is in the agricultural sector and the effects it can have on the spread of AMR. As antibiotics are freely given to food-producing animals, AMR develops within their bacterial flora. This spreads to humans through direct contact, food, or as excreted waste which quickly spreads into the environment through water, manure, and soil. While much of the research and knowledge regarding AMR is focused on human causes, the agricultural sector is often overlooked as a primary contributor. As a result, there are still knowledge gaps in regards to agriculture. Much of the knowledge gap revolves around a lack of surveillance data which up until recently was focused on clinical settings. Not only is surveillance data lacking, but knowledge deficiencies in regards to manure storage and treatment, antibiotic and AMR bacterial uptake in plants, wastewater treatment efficiency regarding AMR gene elimination, the spread of AMR through water, and molecular mechanisms of AMR spread need to be further investigated. Furthermore, most of the current literature examines large-scale agriculture settings in developed countries.

=Sources Cited=


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