Efficiency of Antibiotic Resistance Gene Transfer Mechanisms Term Paper

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Efficiency of Antibiotic Resistance Gene Transfer Mechanisms Upon Exposure to Triclosan

Triclosan has become the latest buzz word in the grocery store. It is being hailed as the ultimate biocide and finds its way into many everyday products such as toothpaste and hand soap. Mass media produced a great amount of hype and convinced the general public that this was necessary to protect them from potentially harmful or even fatal bacteria. Now the use of antibacterial products is being widely questioned by the medical community as it is now known that bacteria can develop resistance to antibacterial agents and that we may be producing a type of super-bacteria. The proposed research will explore the efficiency of antibiotic gene transfer mechanisms upon exposure to triclosan. It is expected that the research will empirically demonstrate that exposure to triclosan significantly increases rate and efficiency of antibiotic gene transfer mechanisms.

Efficiency Of Antibiotic Resistance Gene Transfer Mechanisms Upon Exposure To Triclosan


Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) is a broad-spectrum antibacterial agent which targets the cytoplasmic membrane of both Gram-negative and Gram-positive microorganisms. Tricloson has found its way into many common products on the grocery store shelf. For many years, mass media promoted the use of antibacterial products in everything from toothpaste to toilet bowl cleaners. Now the use of these products has sparked one of the hottest controversies in the scientific world in many years [3] We know that bacteria have evolved to adjust to environmental changes, just as any other living organism that has managed to survive on earth. The ability to adapt to change is the key to the survival of a species. Bacteria are particularly good at this adaptation process. They have evolved to adapt to antibacterials in the environment [3]. This ability to adapt has caused many to fear the by the excessive use of antibacterial products we are promoting the evolution of increasingly resistant bacteria and that this will lead to the evolution of "superbacteria" that could cause an epidemic in the human population.

Rationale for Study

Humans live in constant contact with microbes, the vast majority of which do not cause disease. Pathogenic commensal bacteria have frequent contact with bacteria from many sources found in nature. These commensal bacteria, which often provide a benefit to the host, can serve as reservoirs for resistance genes. Collecting them and holding them for future transmission of other organisms [19]. Ultimately, one of the recipients for this genetic largesse can be a disease causing bacterium.

Bacteria in every environment are constantly evolving, aided in part by the exchange of genetic material. Evidence is growing that extensive horizontal transfer of antibiotic resistance genes occur in nature between clinical and nonclinical bacteria [23]. Hence the commensal reservoir bacteria may be important players in the spread of antibiotic resistant genes. Methods of DNA transfer between organisms include transformation by naked DNA, viral transduction, and bacterial conjugation.

All mechanisms of DNA transfer involve the cell membrane. Since triclosan disrupts the microbial cell membrane, it is important to examine whether triclosan affects the acquisition of antibiotic resistance genes. Experiments would measure the efficiency of gene transfer between different classes of bacteria upon exposure of triclosan.

In the proposed experiment. plasmids carrying marker genes such as those coding for tetracycline and kanamycin resistance will be introduced into several hosts including the bacterium, Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, and Pseudomonas aeruginosa. The efficiency of transformation by naked DNA and gene transfer between bacteria vial bacterial conjugation can be examined upon exposure to various levels of triclosan. Likewise the ability of triclosan to inhibit bacteriophage infection, another common method of gene transfer will be analysed. Our focus on the alterations in the efficiencies of gene transfer mechanisms upon exposure to triclosan may elucidate novel physiological effects.

Significance of Study

In light of the recent media hype concerning the " overuse of anitbacterial agents" including triclosan and the overuse of antibiotics by the medical profession. The question of whether tricloson actually improves the antibiotic resistance abilities of bacteria could have an significant economic and health impact on the general public. If studies show that triclosan actually helps to promote the development of super bacteria, then the companies who have spent so much to promote its use in their products could stand to lose billions of dollars.

In addition, if triclosan does indeed prove to improve the efficiency of the antibiotic resistance capabilities of bacteria, it could have serious health implications for the general public. This research is expected to mirror and confirm previous studies on the subject, which conclude the triclosan does cause bacteria to become antibiotoc resistant.
The confirmation of these studies could lead to a policy change regarding the use and promotion of triclosan as an antibacterial agent.

The results of studies on the effects of triclosan and other agents like it could have a major impact on the production and use of antibacterial agents in common household products. Companies will have to re-develop their formulas and some may have to drop product lines altogether. This could have major impacts on some very large companies. It will also cause a change in the way the public thinks about antibacterial products and their use in the home.

Literature Review

The mechanism of how bacteria work and infect the body have been common knowledge for many years, so have the effects of antibodies in the ability to limit the ability of the bacteria to do harm and cause disease in the human body. Recent media attention to the question of whether antibacterial agents, including triclosan, limited the effectiveness of antibiotics in curing disease, has led to a rash of experiments to test these ideas. The jury is still out and there are no sweeping conclusive results. However, there is sufficient evident to provide background on which to base this research that will be the subject of this study.

The Mechanism of Triclosan

Triclosan works by inhibiting an enzyme that is important to the growth of bacteria. This would seem harmless, except that it trips another genetic switch called the multiple antibiotoc resistance (mar) operon. When this switch is turned on, a pump mechanism in the cell wall expels a wide variety of unwanted chemicals including antibiotics[3] Triclosan essentially allows a bacteria to spit out antibiotics. Sometimes these pumps do not turn off, and when the bacteria replicates, we then have a bacteria that is resistant to antibiotics. This pump mechanism is referred to as the efflux receptor [3].

Triclosan is widely used an advertised, however, there are some who question its efficacy in controlling bacteria. In an experiment by Gilbert, [7], four-day non-brushing studies were used to demonstrate the short-term plaque efficacy of toothpaste containing triclosan, This study showed that there was a statistically significance in the ability of triclosan containing toothpaste in the ability to limit bacterial action in the sample subjects [7]. Other studies confirm these results [1,21]. These results would seem reproducible under the circumstances, but there were many confounding variables that neither were nor identified in all three of these studies. For instance, baselines were not measures to determine the natural level of bacteria in the sample subjects. In addition, nothing is known about the subjects prior to the study as far as dental hygiene and the presence of disease prior to the study.

Mechanism For The Development Of Resistant Bacteria

Natural genetic transformation is believed to be the primary and most commmon mechanism for the acquisition of genetic adaptability bacteria. During bacterial evolution, the ability of Bacteria to adapt to new environments often results from the acquisition of new genes through horizontal transfer, rather than by the alteration of gene functions through numerous naturally occuring processes call point mutations [18]. Horizontal gene transfer is the movement of genetic material between bacteria, other than by descent in which information travels through the generations as the cell divides. Horizontal gene transfer differxs from inherited characteristics of genes as it is commonly described [5]. It is most often considered to be a sexual process in that that requires transfer of chromosomal DNA among two bacterial cells[19].

One of the most common methods for bacteria to adapt to different environmental conditions is through the acquisition of mosaic genes through contact with other bacteria. A mosaic gene is an acquired allele that is obtained through the transformation and combination with the original allele. The result is the formation of a new species of bacteria, that has the characteristics of both parents. It has characteristics of both of the parents, but also some characteristics that are uniquely its own [20].

Often this new bacteria contains a genetic marker that can be selected, such as that used for the antibiotic resistance to tetracycline and kanamycin, or another such marker. In this way horizontal exchange through transformation permits the movement of alleles in bacterial generations. There are many examples of horizontal genetic exchange through both transformation and conjugation in bacteria species that have enabled them to better adapt to their environment [19]. This….....

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