I am isolating a bacteriophage specific for Staphylococcus aureus bacteria from stool samples. I used overnight bacterial culture and NA medium. I pre-incubated for 1 hour for double agar. Why are my zones irregular as in the picture?
It does appear that you have clumps of agar in the agar that was poured into the plate. Whether it did not dissolve, or that it hardened at the edge of the beaker and then was mixed into the still liquid agar when poured is not apparent. You might consider better mixing while heating the agar (and following autoclaving), keeping the mixing going better before pouring, or even pouring at a slightly higher temperature (just be careful for the moisture buildup inside the cover).
Dear Bahar,
The irregular clumps that you see in the plate is the solidified soft agar. You can prevent this by maintaining the soft agar at a higher temprature while you mix the sample (bacteria and phage dilutions) in a tube before adding the soft agar so that you can perform the plaque assay without much ado in a single go. Preferably you can set your hot air oven to 45 degree and maintain the agar there while doing the experiment or a hot plate for the same.
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