Standard Plate Count

These two images show typical results for a standard plate count.  Note the presence of many, small, subsurface colonies (blue arrows).  Colonies growing on the surface (red arrows) spread out more and therefore are larger.  Both surface and subsurface colonies need to be counted, and a plate must have 30 - 300 colonies to be useable for calculation of original cell (colony forming unit) concentration.

 

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Copyright (C) 2004, Steven R. Spilatro, spilatrs@marietta.edu. All rights reserved