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Microbiology Questions

1. How did the theory of biogenesis lead the way for the germ theory of disease?

2. The antibiotic amphotericin B causes leaks in cells by combining with sterols in the plasma membrane. Would you expect to use amphotericin B against a bacterial infection? A fungal infection? Offer a reason why amphotericin B has severe side effects in humans.

3. In a Gram stain, one step could be omitted and still allow differentiation between gram-positive and gram-negative cells. What is that one step and how will the two categories of bacteria appear?

4. Using a good compound light microscope with a resolving power of 0.3 µm, a 10X ocular lens, and a 100X oil immersion lens, would you be able to discern two objects separated by 3 µm? 0.3 µm? 300 nm? Why would, or wouldn't, you be able to do this with the presented microscope?

5. Why can prokaryotic cells be smaller than eukaryotic cells and still carry on all of the functions of life?

6. Distinguish clearly between eukaryotic and prokaryotic cells, giving examples of each type of cell cell (be thorough and organized in your response).

7. In 1861, Louis Pasteur observed that when yeasts grow in a sugar and protein medium, completely free of air, they ferment vigorously; and for every gram of yeast that forms, 60 to 80 grams of sugar disappeared. If the experiment is carried out in the presence of air, for one gram of yeast that forms, only 4 to 10 grams of sugar are removed. The yeasts again ferment if transferred to a sugar-containing medium absent air.
When the experiment is repeated with a protein medium, the yeasts grow only in the presence of oxygen. Pasteur concluded that the yeasts can take oxygen from air, and in the absence of air, the yeasts take oxygen from sugar.
Pasteur applied quantitative methods to his studies of fermentation and was the first to report on organisms that could live and reproduce in the absence of oxygen. His conclusions were, however, incorrect. These different behaviors of yeasts are known today as the Pasteur effect.
1. Explain the three yeast behaviors based on modern concepts of microbial metabolism.
2. What was incorrect about Pasteur's conclusion?

Solution Preview

1. How did the theory of biogenesis lead the way for the germ theory of disease?

Biogenesis is the theory that life originates only from pre-existing life and it says living organisms can be produced only by the development of living germs, while the theory of abiogenesis implies that life may also spring from inorganic matter as such.

The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases. Although highly controversial when first proposed, it is now a cornerstone of modern medicine and clinical microbiology, leading to such important innovations as antibiotics and hygienic practices.

So according to biogenesis theory living organisms can be produced only by the development of living germs.

Experimental proof:
Italian physician Francesco Redi provided proof against spontaneous generation. He devised an experiment where he used three flasks. He placed a meat loaf in each of the three flasks. He had one of the flasks open, another one tightly sealed, and the last one covered with gauze. After a few days, he observed that the meat loaf in the open flask was covered by maggots, and the flask covered with gauze had maggots on the surface of the gauze. However, the tightly sealed flask had no maggots inside or outside it. He also noticed that the maggots were only found on surfaces that were accessible by flies. From this he concluded that abiogenesis is not a plausible theory.
Production of pathogens in the host cell is done by the development of living germs. So if there is infection, then there will be disease, and without infection organism will not get disease. Antibiotics and hygienic practices are developed to prevent and control the disease. Antibiotics are substance produced by a microbe that is used to stop the growth of other microbes. Artificially these antibiotics are taken in as a medicine to control the other microbe which is invaded in the host. Based on the biogenesis theory, germ theory of disease helps to destruct the invaded microbes.
Robert Koch was the first scientist to devise a series of proofs used to verify the Germ Theory of Disease. Koch's Postulates were first used in 1875 to demonstrate anthrax was caused by the bacterium Bacillus anthrasis. These postulates are still used today to help determine if a newly discovered disease is caused by a microorganism. Koch would then be able to hypothesize what may be causing a disease (a living organism) enabling him to conjecture what he should observe in a sick host.
Pasteur's work gave evidence that air itself was not responsible for such phenomena as rotting food and abnormal growths. Inspired by this, Lister took it one step further in that what was responsible could be contained or destroyed. Theorizing that phenol stifled such a cause that resulted in cattle disease, Lister applied this to patients with compound fractures. Although Lister was able to come up with procedures to increase healthy recoveries of such patients, Koch's work was still necessary to actually identify microorganisms which caused disease.

2. The antibiotic amphotericin B causes leaks in cells by combining with sterols in the plasma membrane. Would you expect to use amphotericin B against a bacterial infection? A fungal infection? Offer a reason why amphotericin B has severe side effects in humans.

Amphotericin B is frequently used for the treatment of fungal infections of immunocompromised individuals. It is used to kill fungus that can cause serious or life-threatening infections. Amphotericin B is not effective against bacterial infections or viruses. This medication should only be used for the treatment of potentially life-threatening fungal infections and not to treat less serious fungal infections of the mouth, throat, or vagina in patients with a normal immune system (body's natural protection against infection).

Availability of lipid formulations of amphotericin B has opened up the possibility of treating invasive fungal infections in immunocompromised patients with high doses of this antifungal agent.
Side effects in humans:
Amphotericin B is given intravenously and causes a variety of side effects, including kidney impairment. Most patients experience chills and fever with amphotericin B, but these side effects improve with time and may be reduced by giving other medications before amphotericin B is started. Most patients also develop some kidney impairment, but it is usually mild and resolves after the amphotericin B regimen is stopped. A newer form of amphotericin B, liposomal amphotericin B, is more effective than the older form and better tolerated, causing less fever and kidney impairment. Unfortunately, it is very expensive. Amphotericin B can usually be replaced with itraconazole in one to two weeks after the patient has responded to amphotericin B.
? fever
? chills
? fast breathing
? headache
? changes in heart beat
? dizziness
? fainting
? blurred vision
? nausea
? vomiting
? loss of appetite

The antibiotic amphotericin B causes leaks in cells by combining with sterols in the plasma membrane. Amphotericin B would not work against most bacteria because they lack sterols. Fungi have sterols in their membranes and are generally susceptible to amphotericin B. Humans cells have sterols in their membranes.

3. In a Gram stain, one step could be omitted and still allow differentiation between ...

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