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How Environmental Factors Influence Antibiotic Resistance Guyin (Cice) CHEN
How How Environmental Environmental Factors Infl uence Factors Infl uence Antibiotic Antibiotic Resistance Resistance
Written By Guyin (Cice) Chen Written By Guyin (Cice) Chen Designed By Bianca Vama Designed By Bianca Vama
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Due to the abuse of antibiotics during this century, increased antibiotic resistance from bacteria has become a serious global problem; each year, more than 700,000 people are killed by antibioticresistant bacteria, and according to the World Health Organization (WHO), the fi gure is likely to reach ten million in 2050.1 The environment, being the largest reservoir for bacteria and microbes, plays a signifi cant role in manipulating antibiotic resistant bacteria; specifi cally, soil, animals, and wastewater infl uence the spread of antibiotic resistance. Potential solutions for policymakers include creating global surveillance systems, regulating the use of antibiotics, and controlling the release of wastes and sewage into the environment.
The fi rst antibiotic, penicillin, was discovered by Alexander Fleming in 1928. Penicillin and other antibiotics developed since then directly kill or inhibit the growth of bacteria by interfering with the bacterial cell walls and protein synthesis. They also supplement the immune system when there is an excessive amount of pathogens detected. Although antibiotics kill most bacteria, strains that are resistant to the antibiotics survive and reproduce via natural selection. Over time, the amount of antibiotic resistant strains increases, making it more diffi cult to eliminate them. These resistant strains can also increase in number through Horizontal Gene Transfer (HGT) in which bacteria transfer their resistant genes to neighboring bacteria, causing resistance to spread quickly and effectively.2
However, bacterial infection has progressively worsened due to increases in antibiotic resistance. From 1998 to the present, the widespread dependency on antibiotics in various fi elds, including human health, animal husbandry, and veterinary medicine, have led to the spread of resistant bacteria and viruses. Antibiotic resistance has become an international issue, with WHO declaring it as one of the top ten global public health threats.3
The environment facilitates the spread of antibiotic resistance in several ways, including through the soil, interaction with animals, and intake of contaminated food and water.4
Soil: Largest Storage of Resistant Genes
Soil acts as one of the most important reservoirs for resistant genes. Through manure, sewage sludge, and fertilizers, the soil receives a large amount of excreted antibiotics. This includes improper disposal or handling of drug wastes, contamination of aquaculture and plants, and wastewater streams of some factories. Due to the close proximity of bacteria in the soil, when one strain develops resistance towards a certain antibiotic, the resistant genes can be easily transferred in the colony utilizing genetic exchange mechanisms such as HGT. Bacteria from the soil can be transferred to humans by opportunistic pathogens, which receive resistant genes from human-associated pathogens and then transfer the genes back to humans.4
In a study in China, a total of 36 samples were collected in 2010 from three Chinese provinces in typical large-scale swine farms. Based on quantitative PCR arrays, there were more than 149 unique resistance genes among the samples, with 63 genes being enriched from 192 to 28,000 fold compared to antibiotic free manure and soil.7 Based on the study, there was an increased concentration of antibiotics in both manure and soil in the farm, and the number of resistant genes tripled from the control manure and soil due to resistant gene transfer. It was estimated that resistant genes could be found in one out of two bacteria in the fi eld.1
Animals: Resistant Genes Transporters
Animals can serve as intermediate hosts for resistance genes which then transfer those genes to humans either directly or indirectly.4 Since many farms and companies regularly feed antibiotics to animals to boost their weight and health, a large amount of antibiotics accumulate inside animals’ bodies.
Resistant bacteria then spread from animals to humans via direct consumption. For example, urinary tract infection caused by E. coli is usually transmitted from the food chain.5 Wild birds and animals can also harbor bacteria that carry resistant genes from the environment, including soil, which is
Figure 1: e exchange of antibiotic resistant genes between humans and environmental factors, including air, livestock, crops, antibiotics, feces.
spread through their migration and fl ight patterns. When they encounter humans, the genes can be transferred through consumption or interaction.4
Nutrient-rich animal manure is also often used as fertilizer for crops. Since animal wastes do not undergo secondary treatments, such as disinfection, like human wastes do, resistant genes inside animals’ bodies can enter crop fi elds and farms through their wastes.5
Food and Water Contamination
Contaminated food and water can also play a role in the development and spread of antibiotic resistance. Drinking water from surface water sources can contain antibiotic-resistant organisms.5 Exposure to water that is contaminated by fecal residues can lead to infections. Untreated hospital wastewater fosters the growth of multi-resistant E. coli under various situations. Inadequate infrastructure also
Potential Solutions
Although there are many environmental mechanisms which increase the spread of antibiotic resistant bacteria, there is strong global concern for stopping and reducing the effects of antibiotic resistance.
Policymakers can enact and enforce regulations to reduce antibiotic resistance. For example, global surveillance can be implemented to regulate the exchange of antibiotic resistance across the globe. Currently, Global Antimicrobial Resistance and Use Surveillance System, established by WHO in 2015, works on incorporating data from surveillance of antibiotic resistance in humans, food chains, medicines, and environments. It sets standards for collecting, analyzing and interpreting data between countries.6
Moreover, public health regulation for waste and manure could be implemented and enforced by veterinary and offi cials. Standards for mixed farming and animal manure usage to crops can be developed as well.6 Important policies include use of exactly prescribed amounts of antibiotics and safe disposal of used antibiotics.8 With each mass-scale farm, limited use of antibiotics could be applied for treating poultry, and the waste from the farms can be treated with secondary disinfection before being released into the environment.4 Also, pharmaceutical company employers could help limit the discharge of antibiotic production wastes into the environment through disinfection.6 Policymakers can plan policies accordingly to minimize the threat of antibiotic resistance globally.
Advanced technologies also allow us to reduce the spread of antibiotic resistance. For example, researchers can increase the concentration of antibiotics through potentiation, which manipulates another part of the bacteria to make the organism more sensitive to the antibiotics. Moreover, vaccines can also act as preventative methods to counter antibiotic resistance through preventing infections and decrease the use of antibiotics. More effective vaccines can be developed through manipulating the bacteria’s outer membrane vesicles to make recombinant viruslike particles to eliminate infections. Glycoconjugate vaccines, which use protein carriers to improve immune response to polysaccharide antigens, can also allow the development of vaccines of infl uenzae type B and other targets.10 With the enhanced understanding of antibiotic resistance and rapid development in technology, we could potentially combat this worldwide problem.
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