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Microbiology Study Questions

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1. Clostridium and Streptococcus are both catalase-negative. Streptococcus grows by fermentation. Why is Clostridium killed by oxygen, whereas Streptococcus is not?

2. Assume that after washing your hands, you leave ten bacteria cells on a new bar of soap. You then decide to do a plate count of the soap after it was left in the soap dish for 24 hours. You dilute 1g of the soap 1:106 and plate it on standard plate count agar. After 24 hours of incubation, there are 168 colonies. How many bacteria were on the soap? How did they get there?

3. Why is each of the following bacteria often resistant to disinfectants?
1. Mycobacterium
2. Pseudomonas
3. Bacillus

4. Explain why gram-negative bacteria are more resistant to biocides than gram-positive bacteria. Be specific and descriptive in your response. A description of the differences between gram-negative and gram-positive bacteria should be included, along with an explanation of why any of those differences would have anything to do with the actions of biocides.

5. Ciprofloxacin, erythromycin, and acyclovir are used to treat microbial infections. Ciprofloxacin inhibits DNA gyrase. Erythromycin binds in front of the A site on the 50S subunit of a ribosome. Acyclovir is a guanine analog.
1. What steps in protein synthesis are inhibited by each drug?
2. Which drug is more effective against bacteria? Why?
3. Which drug is more effective against viruses? Why?
4. Which drugs will have effects on the host's cells? Why?
5. Use the index to identify the disease for which acyclovir is used. Why is it more effective than erythromycin for treating this disease?

6. Design an experiment using the vaccinia virus to make a vaccine against AIDS virus (HIV).

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Solution Summary

Clostridium and Streptococcus are both bacteria. The are important microorganisms due to their medical aspect. They cause disease in humans and are quite pathogenic.

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Clostridium and Streptococcus are both bacteria. The are important microorganisms due to their medical aspect. They cause disease in humans and are quite pathogenic.

Clostridium is a strain of bacteria classified as anaerobic. Anaerobic organisms thrive in environments devoid of oxygen. More specifically Clostridium is an obligate anaerobe. This means that when they are exposed to oxygen they will die. Instead of breathing clostridium bacteria sustain themselves by fermentation, a chemical process that converts lactic acid into energy. Streptococcus also creates energy by fermentation, but they are facultative anaerobes. They can also use oxygen for energy when available.

3.Why is each of the following bacteria often resistant to disinfectants?

Following bacteria are often resistant to disinfectants because:
1. Mycobacterium-
Mycobacterium tuberculosis is resistant to disinfectants particularly because the waxy outer coating and complex cell wall of mycobacteria prevents the penetration of various chemical antibacterials. The extra-slow growth rates of these bacteria may also give rise to their reduced susceptibility since disinfectants typically are more effective against actively growing bacteria than against not-growing bacteria.

2. Pseudomonas-
Pseudomonas have the ability to metabolise a variety of diverse nutrients. Combined with the ability to form biofilms, they are thus able to survive in a variety of unexpected places. The ability to thrive in harsh conditions is a result of their hardy cell wall that contains porins. Their resistance to most antibiotics is attributed to efflux pumps called ABC transporters, which pump out some antibiotics before they are able to act and the permeabiliity barrier afforded by its outer membrane LPS. Also, its tendency to colonize surfaces in a biofilm form makes the cells impervious to therapeutic concentrations antibiotics. Moreover, Pseudomonas maintains antibiotic resistance plasmids, both R-factors and RTFs, and it is able to transfer these genes my means of the bacterial processes of transduction and conjugation.

3. Bacillus-
Bacillus forms spores and spores are resistant to many disinfectants. Bacterial spores of the genera Bacillus have been widely studied and are invariably the most resistant of all types of bacteria to antiseptics and disinfectants. The coat(s) and cortex of the spores are associated to the mechanism(s) of resistance presented by bacterial spores to antiseptics and disinfectants. In case of ...

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