Multiplicity of Infection


Upon lysis, different cells release different numbers of phage. The question is why?

One possibility is that the difference is due to the number of phage that infect each bacterium originally, e.g., a bacterium infected simultaneously by two phage might produce a larger (or a smaller) burst than bacteria infected by only one.

The answer is that we don't know if this is true, but we can design an experiment to find out.

If the "multi-infection" hypothesis were true, then as we increase the number phage that infect each bacterium - a number known as the multiplicity of infection or MOI, we should see an increase the average burst size.


Lets do the experiment. We set up three bacterial cultures.

  • Culture A is infected with ~1 phage per bacterial cell. This is an MOI of 1.
  • Infect culture B with an MOI of 2
  • Infect culture C with an MOI of 5

The phage absorb to the bacteria within a minute; now repeat the experiment as we did it last time.

Dilute and aliquot the solution into 50 tubes, and determine the burst size for each MOI.

We have automated this process.   When you push the button, your vTA will determine the number of plates with phage, the number of phage per plate, the mean burst size and the standard deviation



  • Based on your data, is it likely that MOI is the cause of the differences in burst size?

Use Wikipedia | revised 16 December 2004