Horizontal Gene Transfer

My research shows the rise in antibiotic resistant pathogens through horizontal gene transfer. Located in the bacteria are plasmids. They are independent, self-duplicating, and allow bacteria to perform new functions/generate new products. Basically plasmids help their hosts to stop the action of antibiotics and become resistant. “Gene transfer must be integral and critical to the overall survival of bacteria, providing a way for them to adapt to difficult conditions” (Levy 2002, 83). Horizontal gene transfer can occur through conjugation, transposition, transduction, and transformation. These forms of horizontal gene transfer have led to several ways for antibiotic resistant genes to be obtained. The acquiring of these resistant genes allow bacteria to stop the function of antibiotics.
Conjugation is a physical bridge between two bacteria that has cell-to-cell contact. The bacterium produces a fine filamentous protein called a “pilus” (Levy 2002, 83). The pilus brings the donor bacterium and the accepting bacterium together. The donor bacterium then makes a duplicate of its resistance plasmid and gives the copy to the accepting bacterium. Conjugation can also occur when small plasmids that do not have the ability to direct their own transfer ride on the backs of larger plasmids in order to enter a new bacterium. Another form of a
mating system is the use of sex pheromones. Pheromones are substances secreted by bacteria that attract two different cells to attach together. Closely attached bacteria can exchange whole plasmids or pieces of plasmids.
Bacteria can exchange resistant genes without having their plasmid remain in the cell they exchanged with. This is transposition; small segments of DNA called transposons can jump from one piece of DNA to another. Transposons do not rely on any sort of host cell in order to survive and multiply. Professor Ruth Hall from Australia was first to discover integrin, a new kind of transposon. An integrin “acts like a Venus-flytrap it attracts resistance genes to it and then captures them one at time into a single site in the chromosome or plasmid” (Levy 2002, 87).
Transduction is way in which bacteria can transfer a gene to another bacteria through bacterial viruses called bacteriophages. Bacteriophages commonly known as phages can infect only bacteria that have a specific membrane site to attach to. What the phage does is inject its DNA into the bacterium. This transferred DNA can either multiply and kill/explode the cell or find a place on the chromosome. If the phage enters a second host it not only delivers itself but the pieces of DNA it carried along with it from the previous cell. Gene exchange occurs when the phage and the DNA pieces combine into the second host’s chromosome. If a phage happened to pick up a transposon it will also deliver this transposon into the new cell when its DNA is injected.
The last form of horizontal gene transfer is when a bacteria releases pieces of bacterial DNA and is picked up by another bacteria. This gene transfer is called transformation. Once this DNA is picked up by a bacterium it combines and forms part of its DNA. The way this works is that DNA is cut up into pieces and released into the environment for other cells to pick up. According to Stuart B. Levy transformation is principally responsible for the emergence of penicillin-resistant pneumococci (Levy2002, 88).
In 2010 the World Health Organization documented 290,000 cases of MDR TB globally (tbfacts.org). This is just for TB there are many more pathogens out there that are becoming resistant due to horizontal gene transfer. Antibiotics only work if they are able to penetrate the cell and because of horizontal gene transfer many pathogens can use an enzyme that cuts the drug into an inactive form, use a pump to spit out the antibiotic, or alter its microbe so the drug can no longer activate its target (Groopman 2008, 6). There does not seem to be a way to prevent horizontal gene transfer from happening but it can be decreased. This is possible if there are more susceptible bacteria than antibiotic resistant bacteria. If more susceptible bacteria were present this would be the only DNA being transferred during horizontal gene transfer.
Antibiotics “ typically retard bacterial proliferation by entering the microbes and interfering with the production of components needed to form new bacterial cells” (Levy 1998, 47).
I believe a way to decrease horizontal gene transfer in the rise of antibiotic resistance pathogens would be to use the right type and amount of antibiotic needed to kill a susceptible bacteria. If a susceptible bacterium is killed it no longer exists and cannot become resistant. Creating new antibiotics by chemically altering them is beneficial since you will be introducing new drugs never used before to kill both susceptible and resistant
bacteria.
The only way antibiotics will work in our favor is if we use them correctly. “The problem is that we have created the perfect environment in which to bread super bugs that are antibiotic-resistant” (Groopman 2008, 5). Doctors and farmers should only distribute antibiotics when it is a pathogenic disease and should not distribute it constantly in order to prevent future illnesses. Consumers should comply with the doctor and use it as prescribed that way no pieces of bacteria are left that can multiply. Patients should also avoid stocking up on antibiotics or use them after their expiration date because their body may be resistant to the antibiotic already or the antibiotic may be ineffective.
Thank you again for allowing me to present my research before you today. I will gladly answer any questions you may have.