essay questions

2) Edwald’s hypothesis that pathogens in general evolve towards reduced virulence is untrue for several reasons. First of all it has been shown throughout history that pathogens harm their host. One example is the Plague or “Black Death” which claimed millions of people’s lives. The invasive gram negative bacteria responsible for this harm is Yersinia pestis which is a found in blood and lymph nodes. Yersinia pestis has several qualities or virulence qualities which harm its host. First of all it produces protein that induces apoptosis in immune cells. Yersinia pestis is a plasminogen activator NO, plasminogen activator is one of the GENES Y. pestis HAS, NOT what Y. pestis IS. This means that it impairs formation of blood clots, preventing immune cells from going to were bacteria are. Symptoms caused by this bacteria include swollen lymph nodes, fever, chills, and exhaustion. These symptoms caused by the virulence factor lead to death in most all cases. This shows that the pathogen is not interested in the well being of its host. Another example is Streptococcus pyogenes, a gram negative POSITIVE bacteria can cause strep throat and scarlet fever. Both of these are harmful to the host cell (S. pyogenes isn't living inside a host cell, but inside a host organism). In the case of scarlet a patchy rash, high fever, strawberry tongue, blindness, heart problems, or even death result. The negative results to the host cell from Streptococcus pyogenes even further disproves Edwald’s hypothesis. Furthermore there are very few symbiotic relationships between host and pathogens that are symbiotic or that don’t cause harm to the host. Really? What about all the time we spent talking about normal flora? There are way more normal flora bacteria that help us than there are pathogens that hurt us. This harm does not have to be death It can be any symptoms which the pathogen causes. The devastating effects of pathogens are less evident today due to the use of antibiotics. These allow us to reduce the ability of a pathogen to harm its host and the only way this can be done is by killing the pathogen. The comparison of pre-antibiotic effects of pathogens to post antibiotic shows large differences. This means that today with antibiotics less people are dying, but before antibiotics millions of people were. This is because the pathogen was allowed to cause negative effects on its host.

—let me know what you think,

Bri

An analogy: Adolph Hitler killed millions of people. Hitler was a human being. Hitler wasn't the only human being who killed millions of people, either. Other examples include Joseph Stalin, Chairman Mao, and Pol Pot. Thus, human beings are, in general, genocidal maniacs. Human beings who aren't genocidal maniacs are so rare that they can be ignored in any discussion of the goodness or badness of human beings.

3) Gene expression:
Here is what I wrote for the answer to the essay question on Exam 3:
If a high concentration of acylated homoserine lactone was added to a broth culture of JP2, quorum sensing would result. The JP2 bacteria continuously express the autoinducer (AI) gene. Thus, JP2 bacteria are always producing AI receptors. When the high concentratin of AI, acylated homoserine lactone, is added to the JP2 broth, the AI binds to the AI receptor. Then a chain of events occur that produce new sigma factors that lead to the translation, expression of the rhamnolipid and pyocyanin genes, the quorum sensing genes of P. aeruginosa, and the production of biofilms. Quorum sensing is when bacteria in high population density express a gene not normally expressed otherwise. In P. aeruginosa, the genes for both the AI and the AI receptor are continuously expressed. In high density population, the AI binds to the AI receptor resulting in a chain of events that produce new sigma factors which lead to quorum sensing, the expression of the rhamnolipid and pyocyanin genes and the production of biofilms.
~Sam Emerick

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