A bacteriophage is a virus that infects bacteria. In an
experiment, if too few bacteriophages are used for the infection,
it may be difficult to detect or measure the response being tested.
Therefore, it is important to determine the multiplicity of
infection (MOI). The MOI is the ratio between the number of
bacteriophages and the number of bacteria (number of
bacteriophages/ number of bacteria).
1) A 0.1 ml aliquot of a bacteriophage stock with a concentration
of 4 x 109 phages/ml is added to 0.5 ml of bacteria at a 2 x 108
cells/ml concentration. What is the MOI? Show your calculation.
Note that ml stands for milliliter.
2) When the multiplicity of infection is less than 1, is the
probability for a bacterium to be infected by a single phage
smaller, equal, or larger than the MOI? Explain
Hint: consider a case with 1 phage and 2 bacteria, calculate the
MOI and calculate the probability. (4 pts)
3) A culture of bacteria is infected with bacteriophages at a MOI
of 0.2. What is the probability that any one bacterium will be
infected by two bacteriophages? Assume the following:
(a) the attachment of one bacteriophage does not influence the
attachment of other bacteriophages and (b) the attachment of a
second bacteriophage will have the same probability as the
attachment of the first. Show your calculation
QUESTION 1
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