Clinical Microbiology HW#3

CHAPTER 8

1. Mutations that are harmful to cells occur more frequently than those that benefit cells. TRUE

2. An enzyme that copies DNA to make a molecule of RNA is: RNA polymerase

3. Which of the following statements about bacteriocins is false? They cause food-poisoning symptoms.

**TRUE:

They can be used to identify certain bacteria.

The genes coding for them are on plasmids.

Bacteriocins kill bacteria.

Nisin is a bacteriocin used as a food preservative.

4. In the figure (Replication Fork), if base 4 is thymine, what is base 4'? Adenine 

5. If you knew the sequence of nucleotides within a gene, which one of the following could you determine with the most accuracy? Primary structure of protein

6. Genetic change in bacteria can be brought about by: Mutation; transformation; conjugation; transduction

Microbiology Animation: DNA Replication: Overview

1. What are the products of semiconservative replication for a double-stranded DNA molecule?

Two double-stranded DNA molecules, each consisting of one parental strand and one daughter strand.

2. Why is DNA replication essential for a cell?

An organism must copy its DNA to pass genetic information to its offspring.

3. What is the function of the parental DNA in replication?

It serves as the template for DNA replication.

Microbiology Animation: Transcription: Overview

1. Transcription produces which of the following?

mRNA, tRNA, and rRNA are all produced by transcription

2. According to the animation, which of the following makes mRNA from the information stored in a DNA template?

RNA polymerase

3. Ribosomes contain which of the following?

rRNA

4. Which of the following is involved in bringing amino acids to the ribosomes?

tRNA

5. Which of the following can be translated into protein?

mRNA

Microbiology Animation: Translation: Overview

1. What results from the process of translation?

A polypeptide

2. How is bacterial translation different from eukaryotic translation?

Bacteria can begin translation before transcription has terminated.

3. According to the animation, ribosomes move along the mRNA in which direction?

5’ to 3’

Microbiology Animation: Translation: The Genetic Code

1. As shown in the animation, the start codon also codes for which amino acid?

Methionine

2. How many codons code for the amino acid arginine?

Six

3. GAU codes for:

Aspartic acid

4. Which of the following amino acids is coded by only one codon?

Trp

5. What would happen if the mRNA codon that coded for Cys was mutated in the third position from a U to an A?

A stop codon would be introduced prematurely.

Microbiology Animation: Mutations: Types

1. What is considered to be the average natural mutation rate that occurs during DNA replication?

One in every billion nucleotides replicated.

2. A mutation that affects the genotype of the organism but not the phenotype is called a:

Silent mutation

3. A base insertion or deletion in the translated region of the gene may lead to:

Frameshift mutation

4. A base substitution that changes a codon coding for an amino acid to a stop codon is called a:

Nonsense mutation

5. How frequently do silent mutations occur?

Out of every three mutations

CHAPTER 8 READING QUESTION

1. Frederick Griffith did experiments on genetic transformation. Which of the following statements about his experiments is accurate?

Griffith found that DNA released from dead (virulent) bacteria entered live (avirulent) bacteria and changed them genetically, causing them to become virulent.

**This result indicated that the live bacteria obtained genetic information (DNA) from the dead bacteria. In this case, the new genes provide directions for synthesis of the capsule, which allows the live bacteria to become virulent.

MicroCareers: Drug Hunter: Discovering and Developing Novel Antibiotics

Recent years have seen a significant increase in antibiotic-resistant bacteria. Perhaps the best known is methicillin-resistant Staphylococcus aureus (MRSA), which is resistant to beta-lactam antibiotics (e.g., penicillin, oxacillin). The emergence of more and more resistant organisms underscores not only the need for responsible use of antimicrobials, but also the importance of discovering new antibiotics that can treat infections in new ways. You are a microbiologist working in the drug discovery and development (D&D) group at a pharmaceutical company. Drug discovery refers to the actual process of identifying compounds with pharmaceutical potential. While this represents a significant task, it is only the first step in many on the way to generating a new antibiotic. When promising antimicrobial compounds are discovered, development of the antibiotic for commercial use begins. Drug development refers to all of the events that must occur following discovery to move ahead with the drug as a potential therapeutic. This includes everything from the extraction and large-scale production of the drug to designing effective methods of delivery. As you answer the following questions, imagine yourself working as part of the D&D team to identify and validate potential new antibiotics.

1. The project that you are working on was initiated in response to the growing threat of antibiotic resistance in both hospital and community settings. Even in the early discovery and development phase, it is important to think ahead to try to minimize the likelihood that bacteria will be able to evolve resistance to your new drug. Understanding how resistance emerges is an essential part of this process.
Which of the following statements is NOT true regarding the evolution of antibiotic resistance in bacteria?

The exposure of bacteria to an antibiotic causes the bacteria to produce resistance genes.

**In the absence of a selective pressure, such as a certain drug, bacteria that possess genes that confer antibiotic resistance will reproduce more slowly due to the energy expense of maintaining resistance genes. In the presence of a selective pressure, however, the sensitive bacteria will be killed and the bacteria that possess genes that confer antibiotic resistance will have a reproductive advantage. Therefore, over time the genes for resistance will increase in frequency within the population.

2. One approach that is becoming more common in drug D&D is to search for antimicrobial-producing organisms in relatively pristine environments. A pristine environment is one that has been relatively unperturbed by humans and/or domestic animals. Your D&D team is searching for novel antimicrobials produced by bacteria in a remote area of a temperate rainforest in the Pacific Northwest.
Which of the following terms would accurately describe your drug?

Antibiotic; chemotherapeutic agent; natural

**You have found bacteria that demonstrate antimicrobial activity in early testing. D&D chemists on your team have successfully extracted and purified the natural antibiotic from the bacteria. Your focus now turns to microbiological evaluation of the compound.

3. One aspect that must be evaluated during the development phase is the interaction of your drug with the host (i.e., what effect will the drug have on human cells?). There are several important factors to consider in this interaction, including the selective toxicity of your potential drug.
Which of the following statements most accurately describes the principle of selective toxicity?

Selective toxicity refers to the ability of an antimicrobial to kill microbes with minimal damage to the host.

**Your studies using both in vitro and in vivo models indicate that your drug has a high selective toxicity. This means that it is effectively toxic against bacterial pathogens while having minimal toxic effects on the host (eukaryotic) cells.

4. In order to gain FDA approval for your drug, you must elucidate its mechanism of action (MOA). MOA refers to the particular pathway/ process/molecule that will directly be impacted by your drug. Current antibiotic therapies against bacterial infection use one of five characterized mechanisms.

Match each antibiotic (and its functional description) with the appropriate mechanism of action.

Inhibition of cell wall synthesis: Penicillin

Inhibition of protein synthesis: Streptomycin

Disruption of cytoplasmic membrane: Gramicidin

Inhibition of general metabolic pathway: Sulfanilomide

Inhibition of DNA or RNA synthesis: Trifluridine

** Your testing has revealed that your drug has direct effects on the cytoplasmic membrane of bacterial cells. In collaboration with a biochemist on your team, you continue characterization of your molecule and its mechanism of action and determine that it is a small peptide molecule that forms a series of pores or channels in the membranes of bacterial cells.

5. While in the development phase, you are also required to determine both the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for your drug. While these values directly relate to the efficacy of the drug against bacteria, they will also be informative for the next stages of development, which include studies to determine effective dosages within a host.
The picture depicts the results of an MBC test.

 

Based on these data, the MIC for your drug would be 8 ug/ml and the MBC would be 16 ug/ml.

** You have completed some of the important initial steps necessary in the development of a new antibiotic. From here, more extensive testing will be required to determine the effectiveness in a eukaryotic host. Experiments will also need to be conducted in order to determine safe and effective dosage and delivery. While this activity has highlighted some of the important steps taken during the discovery and development of a new antibiotic, it is important to realize that this is a time- and funding-intensive process. In reality, new antibiotic discovery and development can take decades and cost millions of dollars.