A bacteriophage is a virus that infects bacteria. In an experiment, if too few b

Question

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

Explanation / Answer

1) we have 0.1 ml bacteriophage with concentration 4 x 109, that means total number of bacteriophage is

(4 x 109)(0.1)= 4 x 108

Similarly, total number of bacteria are

(2 x 108)(0.5)=108 .

there fore the multiplicity of infection is , 4 x 108// 108=4.

2)One phage can invade, one bacteria, so if the MOI is less than one, the probability of a bacterium still remains equal. If we consider two bacterias and one bacteriophage, that one bacteriophage can infect either of the bacterium equally, so the probability remains equal to the MOI..

3)if we say that MOI is 0.2=2/10=1/5. which means for one bacteriophage, there are 5 bacterias.

so ,the probability of bacteria getting infected by one bacteriophage is 0.2.

Now, given that the attachement of one bacteriophage doesnt affect the other, and the probability of the second one is equal to the first one. Therefore, attack of second bacteriophage wll have the same probablity of 0.2.

Therefore the probablity of the bacteria being attacked by two bacteriophages remains 0.2.

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