EX 29 Viruses, bacteriophage plaques

Bacteriophages

are viruses that infect and replicate within bacteria

• the host is E. coli.

Why would the presence of viruses like bacteriophage be detected in water samples?

Bacteriophage can be used as indicators of fecal contamination in water, as they are present in human and animal waste.

Describe how a viral plaque is formed in lawn

A viral plaque forms when bacteriophages infect and lyse bacterial cells in a solid agar medium

What is the appearance of a bacteriophage plaque in a lawn of bacteria?

the plaque appears as a clear zone within a lawn of bacteria, indicating where the phage has killed the bacteria

What is the purpose of a plaque assay?

to quantify the number of viable bacteriophages (plaque-forming units, pfu/ml)

What is the procedures of a plaque assay?

• serially dilute the phage suspension.

• mix with host bacteria.

• plate on agar.

• After incubation, count the number of plaques to determine phage concentration.

Dilution factor

(volume of phage solution added)/ (total volume after dilution)

Calculate plaques (pfu/ml) from dilution plated.

plaque count (pfu/ml) = number of plaques x dilution factor/ volume plated

Why are only plates with 30-300 plaques counted?

plates with fewer than 30 plaques may be unreliable due to statistical error, while plates with over 300 plaques may result in overlapping plaques and inaccurate counting.

What is the purpose of the control plate in the plaque assay performed?

the control plate ensures the accuracy of the assay by confirming the viability of the host bacteria and verifying the proper conditions for phage growth.