Bauman Chapter 10 Answers to Critical Thinking Questions
p. 288
Why aren’t antibiotics effective against the common cold?
In common parlance, aAntibiotics are only effective againstanti bacterial or antifungal drugs, whereas colds are caused by viruses.
p. 295
It would be impractical and expensive for every American to take amantadine during the entire flu season to prevent influenza infections. For what group of people might amantadine prophylaxis be cost effective?
Elderly individuals, immunocompromised persons or people with respiratory disease who cannot tolerate the vaccine (e.g. allergic to egg white protein) are good candidates for amantadine prophylaxis.
p. 298
Sometimes it is not possible to conduct a Kirby-Bauer or other susceptibility test, either because of a lack of time or an inability to access the bacteria (in an inner ear infection, for instance). How could a physician select an appropriate therapeutic agent in such cases?
The physician first makes the best possible identification of the infecting bacterium by what ever means are available, then selects the broad spectrum antibiotic most effective against the suspected pathogen and its close relatives.
p. 302
Enterococcus faecium (en ‘ter--kok’ s f-s-um) is frequently resistant to vancomycin. Why might this be of concern in a hospital setting in terms of developing resistant strains of other genera of bacteria?
Bacteria are capable of horizontal transfer between cells and even genera of bacteria. Because of the constant exposure to antimicrobial agents in a hospital setting, the bacteria in a hospital are frequently resistant to a variety of antimicrobial agents. The most serious example of this is MRSA (methicillin resistant Staphylococcus aureus) which is resistant to virtually all antibiotics except vancomycin. If MRSA and vancomycin resistant Enterococcus faecium end up in the same environment, the S. aureus could pick up genetic material from E. faecium, resulting in a bacterium resistant to all available antibiotics. While MRSA is the most seriousof great concern, transfer of vancomycin resistance to any pathogens is a serious issue, since vancomycin is currently the ultimate weapon in our antibiotic armory.
p. 312
1. AIDS is often treated with a “cocktail” of several antiviral agents at once. Why is the cocktail more effective than a single agent? What is a physician trying to prevent by prescribing several drugs at once?
The HIV virus rapidly develops resistance to single antiviral agents, and single agent treatments are only effective on the virus for a short time. The “cocktail” of antiviral agents targets several functions at once so that even viruses resistant to one agent are going towill be inhibited by the other agents. By subjecting the virus to several antivirals at once, theThe odds of a virus being able to develop resistance to all of themthe agents simultaneously are extremely remote.
2. How does Penicillium escape the effects of the penicillin it secretes?
Penicillium is a fungus, the penicillin it secretes acts on the peptidoglycan cells walls of bacteria. Fungi have no chemically comparable structures for penicillin to affect.
3. How might a colony of Bacillus licheniformis escape the effects of its own bacitracin?
Since bacitracin is a secreted product, and must enter the cell cytoplasm to have effect, Bacillus licheniformis can escape the effects of bacitracin by altering its cell membrane to prevent entry of the chemical.
4. Fewer than 1% of known antibiotics have any practical value in treatment of disease. Why is this so?
Many antibiotics act on bacteria that are not pathogenic, some are not suitable for standard routes of delivery (ingestion, injection into the blood stream in a water soluble form, etc.) and many of them have such serious side-effects that they can be nearly as dangerous as a bacterial infection. Others are so expensive to prepare their cost is prohibitive.
5. In the summer issue of News of the Lepidopterist’s Society in 2000, a recommendation was made to moth and butterfly collectors to use antibiotics to combat disease in the young of these insects. What are the possible ramifications for human health of such usage of antibiotics?
The use of antibiotics to reduce disease in immature moths and butterflies will result in bacteria that cause lepidopteran disease developing resistance to antibiotics, but the antibiotic resistance will become widespread among other bacteria sharing the environment, and ultimately lead to even greater antibiotic resistance in bacteria pathogenic to humans.
6. Even though aminoglycosides such as gentamicin can cause deafness, there are still times when they are the best choice for treating some infections. What laboratory test would a clinical scientist use to show that gentamicin is the best choice to treat a particular Pseudomonas infection?
A Kirby-Bauer antibiotic sensitivity test of the Pseudomonas strain isolated from the patient will indicate which antibiotic is appropriate for treatment of the infection.
7. Your pregnant neighbor has a sore throat and tells you that she is taking some tetracycline she had left over from a previous infection. Give two reasons why her decision is a poor one.
One reason it is unwise to use “left-over” antibiotics is that the antibiotic may have lost potency and the remaining dose may not be a full course of treatment, in which case the self medication will increase the chance of the bacteria developing antibiotic resistance. (It is also a bad idea to not complete a course of antibiotics as prescribed, for the same reason.) The second major reason that the neighbors’ decision is a poor one is that tetracycline can cause damage to the developing bones and teeth of the fetus.
8. Acyclovir has replaced adenine arabinoside as treatment for herpes infections. Compare the ways these drugs are activated (see Table 10.3). Why is acyclovir a better choice?
Adenosine arabinoside is activated by cellular enzymes and is therefore potentially activated in all cells, infected or not, and may cause damage to the DNA of rapidly dividing cells. Acyclovir is activated by virus-encoded enzymes, and therefore is only activated in herpesvirus infected cells, greatly reducing the chance of incidental damage to the cellular DNA.
9. Why might amphotericin B affect the kidneys more than other human organs?
Amphotericin B damages cells by damaging the cell membrane, which results in disruption the ion balance of the cell. Ion gradients are critical to kidney function, thus drugs that interfere with cellular ion balances result in kidney function decline.
10. Clostridium difficile is an obligate anaerobic opportunistic pathogen. It can cause serious, life-threatening pseudomembranous colitis in patients undergoing long-term antimicrobial therapy. Why might aminoglycosides be used to treat this disease more often that tetracyclines?
Robert. Is there an error in this question? According to the information in Table 10.2, anaerobic bacteria like Clostridium difficile are naturally resistant to aminoglycosides, due to an oxygen-dependent uptake mechanism.
Barbara: This question is mistyped. Fixing it will require a major overhaul. Can we delete it? There is no way to answer the question, hso do we handle its “answer” on the web site?
Robert
I suggest simply stating “This question contains an error, there is no correct answer.”
Nichol