Uninoculated agar plates may stacked and stored upside down in a refrigerator for about 3 months if not used immediately. The inverted position ensures that water does not condense on the bottom of the cover plate and retards the loss of moisture. An inoculated agar plate is also incubated and stored upside down to retain moisture. In addition, the water condensate can act as a medium for transport of cells from one location on an agar plate to another. The slants may be stored in a refrigerator for over a year if culture tubes with screw caps are used.
Incubation of the inoculated plates should last for about 48 hours. They are stored in a refrigerator, and the culture can stay viable for over one month in agar plates or for one year in sealed slants. Prolonged storage of the plates in the incubator dries up the agar and kills the culture. The severe loss of moisture can be visually detected by the appearance of macroscopic cracks that develop in the agar plate.
The used agar plates and other biological wastes should be autoclaved in a pan to destroy all biological activities before being disposed.
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A wide variety of dehydrated medium formulations are available from Baltimore Biological Laboratory (BBL) Microbiology Systems (a division of Becton, Dickson & Co, Cockeysville, Maryland) or Difco Laboratories (Madison, Wisconsin).
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