Hello Shristy,

first you have to make sure that the plaque you took is pure , make a dilution of the phage stock 10^ -8

and propagate with one host bacteria re perform the plaque assay on normal agar media and take a single plaque and propagate with a single host bacteria .

and also, u have to make sure that u used only one specific host to the phage as u should know that the same phage shows different plaques shape and sizes with its different specific bacterial host if it has a host range

and same shape and size with one host

so you have to ensure the purity of the bacterial hosts and the purity of the phage stock

and let me know if u succeed in gaining same plaques shape and size

and Yes, it is possible for a bacteriophage to produce different sizes of plaques when infecting a specific host bacterium. The size of the plaques can vary due to several factors, including:

1. Phage Concentration: The concentration of the bacteriophage in the initial infection can affect plaque size. Higher phage concentrations can lead to larger plaques, as more phages are available to infect and lyse host cells.

2. Host Cell Density: The density of host cells on the agar plate can influence plaque size. Higher cell densities can result in smaller plaques due to increased competition for resources and limited space for phage replication and spread.

3. Phage Adsorption Efficiency: The efficiency with which the phage attaches and adsorbs to the host cell surface can impact plaque size. If phage adsorption is less efficient, it may take longer for infection to occur, resulting in smaller plaques.

4. Host Cell Physiology: Variations in the physiology of the host cells can influence plaque size. Factors such as cell size, growth rate, and metabolic activity can affect the replication and spread of the phage within the host, thereby impacting plaque size.

5. Phage Genetics: Genetic variations within the phage population can lead to differences in plaque size. Mutations or genetic alterations in phage genes involved in host recognition, replication, or lysis can affect the efficiency of infection and subsequent plaque formation.

6. Environmental Factors: Environmental conditions, such as temperature, pH, or nutrient availability, can influence plaque size. Different conditions can affect the growth rate and physiology of the host cells and, consequently, impact plaque size.

It's important to note that plaque size is a complex phenotype influenced by multiple factors, and the specific mechanisms can vary depending on the phage-host system. Experimental analysis, including the characterization of phage and host properties, is often necessary to understand the underlying reasons behind variations in plaque size with a specific bacteriophage-host interaction.

Have a good day!

This is not uncommon, even with a pure phage stock you can still observe different plaques sizes. You might get a bit more even conditions if your host cells are still in growth phase and not overnight cells.