I agree, sterile culture flasks are not likely the problem. Check or
better still throwout medium,etc. You may consider adding an antifungal
agent to your new medium. However, if you are sure that the problem is
contaminated plates you can:
1. soak them with enthonal (>70%) an let them air dry in a tissue
culture hood with the uv light on (Note: don't leave them under UV light
longer then require; UV light has a habit of leaching plastic.)
2. expose your plate to formaldehyde vapour, that will kill anything.
You should then clear your incubator and leave a beaker of formaldehyde
in the incubator overnight. Before placing the cells back into the
incubator be sure to properly ventilate the incubator (otherwise
your cells will die).
