Pre-Lab #8 Flashcards
What is a bacteriophage?
a. Viruses that infect bacteria cells, most abundant and diverse biological entities on the planet
Are bacteriophages harmful to humans? Why or why not?
a. No, they are not harmful to humans. They only infect certain species of bacteria cells by recognizing very specific receptors on the surface
Provide three potential uses for bacteriophages.
a. Phage therapy
b. Bio control in Agriculture
c. Food and Safety
When performing a plaque assay, which one is serially diluted—the phage or the bacteria?
a. Phage (virus) is diluted
What is a lytic bacteriophage?
a. Replicate within bacterial cells and exit the bacterial cells by causing the cell to lyse or burst. Their progeny invades the surrounding bacteria, thus producing clear plaque
What is a plaque forming unit (pfu)?
a. A measure of infectious viral particles
How do you determine the concentration of phage in a sample?
a. Plaque assay
i. Serial Dilution
ii. Inculcated with a host cell
iii. Incubation
iv. Counting
v. Calculating phage concentration
What is the difference between the T4 and T4r bacteriophages that we will be using in Lab #8?
a. T4 plaques are characteristically 1-3 mm in diameter with a diffuse (turbid) outer perimeter. The turbidity at the edge of the plaque is a result of decreasing lytic efficient in the turbid region. This is mostly due to a phenomenon known as lysis inhibition
b. The T4r phage is a rapid lysis mutant of the T4 phage. It produces slightly larger plaques that have a much sharper edge. Plaques formed by “rapid lysis” strains, do not have turbid edges because these mutant phages, do not exhibit lysis inhibition
Compare and contrast the expected size and plaque morphology of the T4 and T4r bacteriophages.
a. T4 is smaller in size about 1-3mm while T4r are larger in size
In this lab, you will use a double layer overlay method to potentially isolate lytic bacteriophage infections. For this technique, phages and the appropriate bacteria are mixed in a small volume of soft agar medium. This mixture is then poured onto a plate containing hardened agar medium that provides a base for the more fragile upper layer. The result is a plate containing two layers, the top layer comprising the mixture of soft agar, phages and bacteria, and the bottom layer containing the hard agar upon which the top layer rest. The plate is then incubated overnight at 37°C. What do you think the top layer of agar will look like after the double-layer agar plate is incubated at 37°C? Will it look clear as it did prior to incubation? Why or why not?
a. I think that the top layer will not look clear as it did. I think it will be cloudy because there will be a bit of growth on the plate after incubation
What effect do you think the presence of the phages will have on the appearance of the plate containing E. coli? To help answer this question, review the description about what happens when a phage with a lytic life cycle infects a bacterium.
a. I think it will allow for phages to form. The phages will infect the E. coli, and then the cells replicate, and the E coli cells will burst. And phages will form
