Monday, January 10, 2011

Culturing Bacteria

A student is culturing some mouth bacteria to compare between humans and canines.  Would it be possible to have a microbiologist identify the bacteria for the type and “amount” somehow?  He will measure the size of the culture on the plate each day but there is probably a better way to quantify the bacteria than measuring with a ruler.  He’ll identify it the best he can with the resources we have, but we thought a microbiologist may have access to better identification tools.  We could also send pictures of the bacteria if they don’t want us to send the agar plates.

Response by Science Posse Fellow Ashley Driscoll

"To estimate "amount" of bacteria a common method is OD600, using a spectrophotometer at 600 nm to measure Optical Density.  The turbidity of the solution is related to the number and gives a pretty good order of magnitude estimate.  One can get a fairly good idea of Genus with colony morphology, size, shape and color, and with a Gram Stain (  A good reference is Brock Biology of Microorganisms and I'm looking for my Microbiology class notes that might help."


  1. Good post, information not known to everyone. If knowledge is key for everything then one should grab it without thinking from where it is coming.