Antibiotic Resistance in Livestock and Humans - Essay Example

Antibiotic Resistance in Livestock and Humans For many years, antibiotic drugs have helped turn previously life-threatening bacterial infections to treatable conditions. Further, antibiotics are used to improve livestock yields by preventing infections and stimulating growth in farm animals. However, the unnecessary administration of antibiotics in healthy farm animals and excessive application in fertilizers has led to high residual levels. The major concern is that antibiotic overuse in livestock presents increased risk for the emergence of resistant strains in livestock and humans. Antibiotics are antibacterial agents used in the treatment of bacterial infections. Bacteria are microorganisms present in many water and soil habitats. These microorganisms are diverse in terms of shape, size and ability to cause infections. While many of bacteria species are non-infective, some strains cause infectious diseases including respiratory diseases such as tuberculosis, cholera, anthrax and many others. Antibiotics are increasingly being used in agriculture to prevent and treat bacterial infections in livestock. Antibiotic agents are also being used in livestock feeds and water to prevent and control bacterial infections. This therefore suggests that different types of antibiotics are being given to healthy livestock. These drugs accumulate in the body, creating antibiotic residue that is eventually eliminated from the system if the drugs are discontinued. However, the increased use of antibiotics in livestock has raised concerns about growing bacterial resistance against these drugs. Current efforts in agriculture focus on producing healthier livestock. This trend has led to increased use of antibiotics to promote growth, fight infections and compensate for unsanitary rearing conditions. However, the accumulation of antibiotics in food animals (antibiotic residual) poses significant risk to humans. For instance, antibiotic overuse in livestock as been associated with increased antibiotic drug resistance in humans. This leads to high levels of the drug in the system of these animals. High concentrations of the drugs kill most of the bacterial strains in these animals, especially the strains that are sensitive to the particular drugs or drug combinations. However, the sustained exposure of bacteria to antibiotics leads to the selection of bacterial strains that have the capacity to withstand high drug levels. These bacterial strains develop resistance to the drug and their relative population exceeds that of the sensitive bacterial species. This is especially important given that the number of sensitive strains reduces due to increased drug levels. On the other hand, the antibiotic-resistant strains grow fast despite the accumulation of the drugs. Bacteria have evolved mechanisms for gene transfer, a factor that enables these microorganisms to adapt to new environments such as the threats posed by antibiotic accumulation. Bacteria do not reproduce sexually; rather they undergo asexual cell division which enables vertical gene transfer. While this type of reproduction is expected to limit their ability to survive harsh environments, bacterial species have evolved mechanisms to offset this limitation by exchanging genetic material via horizontal gene transfer. In horizontal gene transfer, different bacterial species exchange genetic information via transformation, conjugation or transduction (Dutta and Pan, 2002). Transformation involves the uptake of genetic information, usually short naked DNA fragments or parts of a chromosome. This is a common method of gene transfer especially for naturally transformable bacteria. Gene transfer via conjugation involves cell-to-cell contacts and may entail exchange of longer DNA fragments (Dutta and Pan, 2002). Conjugation involves conjugal plasmids or transposons and is common among distantly related bacteria. Plasmids are circular self-replicating DNA molecules found in bacteria. These DNA molecules can be transferred to recipient cells or taken up by bacteria species via transformation. Transposons are genetic elements in bacteria with the ability of mediating self transfer from one region is a chromosome to another region on the same chromosome or in a different chromosome. Transposons achieve this function by synthesizing specific substances, transposase enzymes which facilitate genetic recombination. On the other hand, transduction involves the transfer of genetic material by phage, especially in closely related bacterial species (Dutta and Pan, 2002). Bacteriophages are viruses that infect bacterial cells by harnessing the host translation machinery. The phage particles are formed in donor bacterial cells during development and are involved in transduction. Horizontal gene transfer results to the introduction of DNA sequences that share some similarity between the donor and recipient DNA. This similarity is called homology, an important factor in enabling stable incorporation of the donor sequences to the recipient chromosome. The donor sequence in this case refers to genetic materials such as antibiotic resistant genes while the recipient chromosome refers to the genetic material of the antibiotic sensitive strains. The final transfer involves genetic recombination, a process that involves insertion of genetic material from a different bacterial strain (Thomas and Nielsen, 2005). The integrated sequences from antibiotic-resistant bacterial strains contain genes for antibiotic resistance. The horizontal gene transfer results in the increased spread of antibiotic resistance. People become infected with drug-resistant bacteria by consuming products such as meat and diary products from infected livestock (University of Arkansas, Food Safety Consortium, 2008). In addition, people handling food animals and those working in farms and slaughter houses are exposed to antibiotic-resistant bacteria. Farm wastes and runoff from slaughterhouses enter water sources such as ground water, lakes and rivers or are spread on agricultural fields as fertilizer. The antibiotic-resistant bacteria are ingested from vegetables planted in manure-treated soils and or from drinking water contaminated with animal wastes. There is growing concern that meat animals treated with antibiotics are a major source of antibiotic resistance pathogens in people. The usage of antibiotics in food animals such as in poultry, pork and beef is widespread. Many antibiotics are administered to animals to promote growth and increase yields, especially in factory farms. However, the greatest concern is that livestock-associated strains of bacteria have been found in humans. For instance, staphylococcus aureas and salmonella strains have been isolated in man (Adams, 2012). In a 1984 report, it was reported that pathogenic campylobacter similar to that found on poultry products was found in people presenting with enteritis symptoms (Adams, 2012). About 30% of the bacteria isolated from these people were resistant to tetracycline drugs (Adams, 2012). Pathogenic antibiotic-resistant strains of bacteria have also been found in people who work with farm animals. Antibiotic-resistant strains associated with livestock have also been isolated in farm workers. Given the increased risk to human health, it would be fair to consumers and farmers to outlaw antibiotic overuse in livestock. A critical analysis suggests that the spread of antibiotic resistance is partly due to unnecessary use in healthy livestock as an alternative to sanitary measures. The actual danger of antibiotic resistance is even larger considering the escalating cost of healthcare and drug development. Similarly, the potential overuse and unorthodox administration of antibiotics in farm animals could result to the emergence of resistant diseases and eventually lead to poor yields. References Adams, J. (2012, January 09). FDA changing course on antibiotics in livestock. Los Angels Times. Retrieved November 3, 2012 from http://articles.latimes.com/2012/jan/09/health/la-he-antibiotics-agriculture-20120109 Dutta, C. & Pan, A. (2002). Horizontal gene transfer and bacterial diversity. Journal of Bioscience, 27, (1), 27-33. Thomas, C. & Nielsen, K. (2005). Mechanisms of, and barriers to, horizontal gene transfer between bacteria. Nature Reviews Microbiology, 3, 711-721. University of Arkansas, Food Safety Consortium (2008, February 22). Pathogen Resistance To Antibiotics In Animals Could Lead To Resistant Human Pathogens. ScienceDaily. Retrieved November 3, 2012, from www.sciencedaily.com­ /releases/2008/02/080220231456.html Read More