Question

1. In a bacteriophage growth curve, what happens during the latent period?

2. Why is the initial bacterial culture greatly diluted after the bacteriophage adsorption step?

3. How would you define burst size?

4. Why is the water bath for the top agar held at 45C and not at 100C the melting point for agar?

Answer 1

1) Latent period immediately follows phage addition and thus there is no release of virions. During this phase, the infection, adsorption, injection and synthesis of new viral DNA and protein coat occur. At the end of this period, the phage virions increase in number within the host bacterium and the host bacterium is prepared for lysis.

2) The bacteria are mixed with phage and incubated for a short period of time. The mixture is then diluted drastically to reduce the number of bacteria available for phage adsorption. Some phage particles fail to meet susceptible bacteria (due to the dilution of the adsorption mixture) and thus remain free in the culture fluid. Phage dilutions should be made into the adsorption media so as to avoid carry over of ingredients found in phage diluent.

3)The term burst size is the number of viruses released from a single infected bacterium.  

4) Top agar must be maintained at 45-50°C until immediately before use as higher temperatures will kill bacteria and the lower temperatures will allow agar to solidify prematurely.