Experiment 18 - Bacteriophage Assay

What are viruses

They are obligate intracellular parasites, submicroscopic and filterable

What are viruses composed of?

• Nucleic acid core

• Surrounded by protein coat or capsid

What are the characteristics of bacteriophage?

• Many sizes and shapes

• Contain DNA or RNA (NEVER both)

What are the most complex phage?

T-even

Why are the T-even phages the most complex?

They have a polyhedral head and a contractible tail

How does replication occur of bacteriophages?

Only within living bacteria

What is host specificity?

Where a bacteriophage for one strain of bacteria may not attack another strain of the same species

What is the lytic cycle?

The process by which phages infect the cell (injection of phage nucleic acid), the replication of more phage particles, and the destruction of the cell + release of virions

What does a cell surface have?

Many receptor sites and is capable of adsorbing many phage particles (only one phage injects itself)

What is a ghost?

The empty phage coat left outside the cell

What is the burst size?

The number of particles liberated per hosr cell

What is the latent period?

The period of establishment of vegetative phage state before liberation of new virions.

What happens if the lytic cycle occurs in a broth culture?

The turbidity decreases

What happens if the lytic cycle occurs on an agar plate culture?

Plaques are formed

What are plaques?

A clear area produced by the destruction of cells during cycles of phage replication on the lawn of host cells

How do plaques occur?

New phage attack adjacent host cells and destroy them, causing for the increase of clearing size

How can the number of phage particles be estimated?

By the serial dilution procedure if the multiplicity of infect is kept low

What are the purpose of plaque counts?

They are used to calculate the density of infective particles in the phage stock

What is the ideal assay for calculating original phage titer?

Between 30 and 300 plaques