Antibiotic Resistance in Livestock

Antibiotic Resistance in Livestock

Abstract

          For the past 70 years, antibiotics have been used in the feed of commercially farmed animals. This was done to prevent diseases and infections from spreading between the animals. The use of antibiotics on livestock also promotes growth, and this all helps meat prices stay affordable. The problem with using antibiotics is that their overuse has led to antibiotic-resistant bacteria that are extremely difficult to treat and can be deadly. Antibiotic-resistant bacteria are easily spread throughout the environment when animal waste is used as fertilizer. People can also contract antibiotic-resistant bacteria from eating contaminated meats. In this review, the reasons why antibiotics are used in livestock will be discussed. This review will also discuss the dangers of antibiotic-resistant bacteria and possible methods on how antibiotic resistance will be reduced.     

Introduction

      Without the use of antibiotics farms, there would be an increase in the number of animal deaths, and the growth rate would slow down. The agriculture industry has become dependent on antibiotics to keep up with the demand for food. But this does not justify the overuse of antibiotics. Antibiotic resistance is one of the most pressing issues that global health organizations are facing. The overuse of antibiotics in the livestock industry has contributed a great deal to this problem. Every passing year resistant strains grow stronger, and infections that used to be easily treated with simple antibiotics have become deadly and untreatable. The struggle to control this pandemic has been going on for decades with little to no results. This paper will discuss how and why antibiotics are used in animal feed. This will also discuss how the overuse of antibiotics has led to the increase of antibiotic resistant bacteria, and the dangers that it possess to people.

Why Antibiotics Are Used for Raising Livestock

         Antibiotics have been used in livestock since the 1950s. Commercial farm animals are usually kept in crowded, stressful environments that make them susceptible to contract numerous diseases and infections that could lead to the loss of many animals [1]. Typically, antibiotics are used in livestock feed to prevent diseases and infections that would lead to death in the live stocks. Another reason antibiotics are used for raising livestock is that it promotes growth in the animals that are treated [2]. It has also increased the feed conversion ratio because some medicines can illuminate certain types of bacteria in the intestinal tract. This allows the animals to produce more muscle and fat quicker than untreated livestock. For example, the addition of antibiotics in pig feed has increased the average weight gain 3.3-8.8% [3]. With a growing world population, farmers have to resort to methods such as using antibiotics to meet the ever-growing demand. Since medicines improve the survival, and growth rate of livestock allows meats and animal products to be more affordable to consumers. Without the addition of antibiotics to livestock feed, there would be a higher percentage of food animals that would die from diseases and infections. For example, since Europe has banned the use of antibiotics in livestock feed, Denmark which is the world leading exporter of pork has seen the numbers of farmed pig’s death increase by 25 percent. They have also seen an increase in the number of newborn pigs dying from illnesses with 21% out of the 32 million piglets not making it [3]. 

Antibiotic Resistance dangers

     More than 70% of all the antibiotics produced in the U.S. is used for livestock. This overuse has led to bacteria becoming more resistant to antibiotics [4]. This overuse is a result of natural selection, random mutations, horizontal transfer of immune genes, and the inheritance of genes.  A chronic undertreatment in food animal farming has promoted the emergence of immune genes. This is a consequence of low levels of antibiotics added to the feed of livestock. Animals are also given more antibiotics when they show signs of illness. For example, dairy cows are usually given penicillin if they show symptoms of mastitis. Pigs and poultry are given tetracycline when they show symptoms of raspatory diseases. Fish farms and orchards use various forms of tetracyclines and other antibiotics when there is a suspected fungal or bacterial outbreak present [5]. As the antibiotics kill off the bacteria that are sensitive, a few resistant cells remain. These cells then reproduce and horizontally transfer immune genes to surrounding bacteria. As a result, antibiotic resistance has increased due to the overuse in farms along with the overuse in people.  

Antibiotic-resistant bacteria have the potential to be one of the most dangerous infections. The number of patients that have been hospitalized in the U.S. with infections from antibiotic-resistant bacteria has increased 359% from 1997 to 2006 with, 37,005 cases in 1997, and 169,985 in 2006 [6].

Figure 1. Methods of Contamination. This diagram produced by the CDC show how antibiotic resistant bacteria can spread and infect people and animals [7].

                    The latest reports conclude that every year in the U.S. there are over 2 million people who contract antibiotic-resistant bacteria with 23,000 deaths on average [8]. There are many ways to contract an antibiotic-resistant bacterium. A common way is by consuming undercooked animal meats that are contaminated with animal waste. Since most of the resistant microbes live in the intestines when the animals defecate, they are essentially infecting their surroundings. For example, cow feces contain millions of microorganisms including antibiotic-resistant bacteria that have the potential to affect humans and other species when used in fertilizers. Researchers from Yale where able to extract 80 genes from bacteria from within the cow’s intestines that are responsible for making the bacteria antibiotic resistant. This concluded that cow manure used for fertilization is spreading antibiotic resistant gene through the environment that will eventually infect soil, crops, and groundwater before making its way to humans. Figure 1. Illustrates how antibiotic resistant bacteria spreads throughout the environment through people and animals [9]. Antibiotic resistant bacteria spread fast just like any other bacteria. For example once one animal in a commercial farm gets infected with a antibiotics resistant microbes it can spell disaster for all the surrounding animals costing farmers millions every year.

           Salmonella and Campylobacter are the two most common bacteria that people tend to contract, and resistant strains for both have been on the rise. For example, Newport 9+ is an antibiotic-resistant strain of Salmonella that has been increasing in frequency. This strain is called Newport 9+ because it is resistant to nine antibiotics including ceftriaxone which is known to kill most bacteria. The Newport 9+ strain originated from Salmonella typhimurium which is found in livestock. Treatment is difficult for antibiotic-resistant bacteria due to the lack of pharmaceutical companies producing new medications to help combat the growing problem of antibiotic-resistant microbes [4].  

 Efforts to Reduce the Impact of Antibiotic-Resistant Microbes

            Efforts have been made in the past to attempt to battle the rising numbers of antibiotic-resistant bacteria. The first attempt was formed in 1978 The FDA tried to ban the use of antibiotics in some agriculture practices, and the pharmaceutical companies resisted these regulations claiming there wasn’t sufficient evidence that the use of antibiotics in livestock is causing antibiotic-resistant bacteria. Since then the evidence and knowledge of bacterial resistance have grown. In 2000 the FDA, CDC, and USDA sighed a draft to coordinate an 11-step federal response to the growing issues of antibiotic resistance [5]. In 2016 the O’Neil commission published a list of recommendations to reduce the use of antibiotics worldwide. The goal was to put in place a global organization that would educate the public about the dangers of antibiotic-resistant bacteria [10]. Its purpose was to also reduce the unnecessary use of antibiotics in livestock farming in hopes of reducing the number of resistant bacteria that make it out into the environment.  

              CRISPR-Cas9 is a genome-editing tool that has massive potential for reducing the impact of antibiotic-resistant bacteria. CRISPR-Cas9 can be used as an artificial immune system designed to protect bacteria from foreign nucleic acids that would cause the bacteria cell to become resistant to antibiotics. CRISPR-Cas9 is also capable of removing specific genes that allow bacteria cells to be resistant to antibiotics. This is possible because two important molecules which are Cas9, and guide RNA (gRNA). The Cas9 enzyme performs like a pair of scissors and cuts the two strands of DNA at the desired position where the genome with be taken out or placed. The guide RNA is responsible for finding the target sequence location and binding the Cas9 enzyme. Even though there is a lot of potential for CRISPR-Cas9 to battle antibiotic resistance in bacteria, CRISPR-Cas9 still needs to be studied more intensively. This is because CRISPR-Cas9 has only been used on cloned E. coli cells, and in the real-world application, it would be much more difficult to carry out. 

Conclusion

            Despite advancements in understanding of antibiotic resistance it will be an issue that will be dealt with for a while. This review has gone over the reasons why antibiotics are used, and the dangers it brings to the public. Many organizations are raising awareness to the issue. Maybe one day CRISPER-Cas9 can help reverse the resistance in microbes but until then educating people and farmers on how to responsibly use antibiotics will be the most effective step in battling antibiotic resistance.

Works Cited

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