Term Paper: Efficiency of Antibiotic Resistance Gene

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[. . .] What is Known about Tetracycline?

Tetracyclines and its derivatives are antibiotics which inhibit the bacterial growth by stopping protein synthesis in the bacteria. Bacteria must synthesis proteins into energy in order to survive, mush in the same way we synthesize fats, carbohydrates, and proteins into energy that can be used in our body's various systems. Teetracycline compounds have been widely used for the past forty years as therapeutic agent in medicine. The emergence of bacterial resistances to these antibiotics has n limited their use in recent times. Three different specific mechanisms of tetracycline resistance have been identified: tetracycline efflux, ribosome protection and tetracycline modification [23].These are common mechanisms found in other situations and will be discussed in detail.

Tetracycline efflux is acccomplished through thhe use of an export protein from the major facilitator family [23]. The export protein functions as an electroneutral antiport system that promoted and enables the exchange of a tetracycline cation complex for a proton [26]. The difference between the mechanisms in Gram-negative and Gram-positive bacteria is in the chemical used to achieve thiis effect. In Gram-negative bacteria the export protein contains transmembrane fragments (12 TMS), whereas in Gram-positive bacteria it displays another transmembrane fragmetn (14 TMS). Ribosome protection is mediated by a soluble protein which shares homolgy with the GTPases participating in protein synthesis [22]. The third mechanism involves a cytoplasmic protein that chemically changes tetracycline. This reaction takes only place in very specific environemtnal conditions and does not function in the natural host [28].

Several tetracycline resistance markers are currently being used in molecular biology. This feature has also been exploited to construct tightly regulated expression systems by using the regulatory elements of the Tn10 tetracycline operon. The tetM gene from Tn916 which can be expressed both in Gram-positive and Gram-negative bacteria is also frequently used [23]. These genes provide a measurement system and tools for the measurement of genetic material transfer between bacteria.

Many studies have been conducted that concluded that the environment of the bacteria may help influence the ultimate host range of specific tet genes. If the trend is reversed towards the development of inreasingly antibiotic-resistant bacteria, it would lead us to consider the need to change how antibiotics are used in both human and animal health as well as food production [22].

This is the general opinion, that has been held by many scientists who are in support of lessened usage of antibacterial compounds. However there are those who disagree and consider them to be a valuable asset to society. These persons continue to promote their use. Some feel that the effects have not been studied extensively enough to make a conclusion that their use leads to genetic mutations making the bacteria resistant antibiotics [31]. Yet these same persons still express that we should limit the use of antibacterial agents until more studies have been conducted.

The Reason for all the Media Hype

Levy [11,12,13,14,15,16] attributes the increased occurrence of resistant strains of bacteria to the overusee of antibiotics by physicians and the public at large. Levy has been a key promoter of the movement to limit the use of antibiotics an antibiotic agents. He feels that there are many factors, not attributable to science that have led to this phenomenon. Levy feels that these reasons are [11,12,16] that the fear of litigation and the perception of patient expectations are a contributing factor to antibiotic misuse and, therefore, bacterial resistance. The increased consumer demand for and stockpiling of antibiotics plays a larger role in promoting the use of products that increase bacterial resistance. Travel has increased spread of resistant bacteria.

Levy also blames some advances in medical science for the spread of resistant bacteria including advances in treatment of such conditions as cancer and transplant procedures that leave patients vulnerable to infections with bacteria bearing intrinsic antibiotic resistance. Often immunosuppreseants are used in these procedures.

Levy states that there have been many new strains of bacteria appear that were previously not clinically significant in the past. Some previously benign bacteria have mutated to become harmful. In addition, some harmful strains are becoming more difficult to treat with conventional antibiotics. This means that as bacteria become more resistant, we will have to develop new compounds to combat them and they will continue to change. This will lead to a constant race between scientists and bacteria in order to have effective treatments. This is essentially the basis behind the "superbacteris" phenomenon that has been the subject of the media hype in recent years. The works of Levy are primarily responsible for this publicity.

Bacteria have developed the resistance to multiple antibiotic compounds and these bacteria have become an increasing problem in hospitals[25]. An intersting phenomenon has been found in farm workers that use subtherapeutic levels of drug given to animals to promote growth. The workers and animals all contain multidrug-resistant strains of Escherichia coli, a bacteria that could have significant clinical results in the workers [15].

Throughout his many published works, in both popular and peer-reviewed magazines and journal, Levy draws several generalizations about the use of antibiotics and antibacterial agents by the general public and the health professions. The first is that the numbers of outpatient antibiotic prescriptions and over-the-counter availability of antibiotics in developing countries promots drug resistant strains. This availability to the public creates a situation where even if healthcare professionals see a need to limit their use, they are not in a position to have an impact. The public would have to be convinced, and presently there is a massive media campaign by the manufacturers to promote their use. This exaggerated use of antibiotics and antibacterials in the home will increase the incidence of resistant bacteria in other members of the household[16].

Levy points to other problems in the continued overuse of these products. The disposal and excretion of antibiotics into the environment can change the microbiology of a region [15]. This could result in localized epidemics of resistant bacterial strains that could then begin to spread to other regions. When triclosan, is added to antibacterial cleaning products for the home, leaves residues and remains in sewers and on household surfaces, allowing resistant bacteria to emerge [15]. One incidence of a bacteria where this has happened in that the occurrence of multidrug-resistant Staphylococcus aureus is increasing worldwide, in the community as well as the hospital. Antibacterial products in homes may contribute to the problem [15]. This is the bacteria responsible for the widely publicized flesh-eating skin disease that had been sensationalized by the media.

Levy also explores teht duration of the resistance to antibiotics. He concluded that resistance may be transient with short courses of antibiotics. However, long courses of therapy encourage the development of permanently resistant strains [30]. Once resistance to a drug appears, it cannot be eradicated. However, measures can be taken to minimize the spread of resistant bacteria and promote repopulation with susceptible bacteria [24,27,29].

Some bacteria are inherently resistant to antibiotics, whereas others accumulate genetic resistance in addition to their intrinsic resistance. Changes in bacterial phenotypes are relatively simple to make, since these organisms have only one chromosome [4]. In addition, plasmids replicate independently of the chromosome but transfer resistance through the genes they carry. Bacteriophages can infect cells and introduce resistance genes. Plasmids can also move from one baterial species to another for example from Salmonella to Escherichia coli [6,9, 17].

The wide spread use of compound that promote antibiotic resistant bacteria is staggering, emphasizing the urgency in making a determination of results and recommendations for usage. Hooten makes the following statements regarding the severity of this overuse

Plant and animal farming may account for twice as much antibiotic use as in humans in the U.S. Other data indicate that 35 to 50 million pounds of antibiotics are produced annually in the United States. Hundreds of thousands of pounds are sprayed onto fruit trees each year, causing a large geographic spread of drugs and therefore drug-resistant bacteria. In animals, as much as 80% of antibiotics is given to promote growth. Mash made from carcasses containing bacteria that produce tetracycline for human use was accidentally discovered to promote growth through traces of tetracyclines left after extraction. After this finding, companies began to add tetracycline and penicillin to feed intentionally. The levels of drug given are subtherapuetic but sufficiently high to select for resistance. As a result, in the 1970s, farm workers and animals were found to harbor multidrug-resistant E. coli. Levels of resistance were once thought to correlate directly with dose, but this has been disproved, since for many antibiotics, resistance is mediated by genes conferring high levels of resistance" [8, p. 1089-1090].

The concern over this problem stems from the occurrence of multi-drug resistant bacteria in the community at large. They used to be confined to certain situations and locations, such as in hospitals and on farms [3,11, 16]. This has been especially common regarding… [END OF PREVIEW]

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Efficiency of Antibiotic Resistance Gene.  (2002, November 28).  Retrieved June 19, 2019, from https://www.essaytown.com/subjects/paper/efficiency-antibiotic-resistance-gene/8172759

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