#Microbiology dilution math how to

The agar plate allows accurate counting of the microorganisms, resulting from the equal distribution across the agar plate. The procedure described above produces a set of pour plates from many dilutions, but spread plates (sample spread on top of solidified agar) can be used also. Colonies grow within the agar, as well as on top of the agar and below the agar (between the agar and the lower dish). As it would usually be impossible to actually count the number of microorganisms. The agar solidifies, with the bacterial cells locked inside of the agar. Serial dilutions are used to calculate the concentration of microorganisms.

A set of serial dilutions is made, a sample of each is placed into a liquefied agar medium, and the medium poured into a petri dish.

This protocol is specific for bacterial counts (colony-forming units, CFUs), but can be modified for fungi (CFUs) and viruses (plaque-forming units, PFUs for viral counts). The purpose can be determination of bacterial, fungal, or viral counts (indirectly). The following is a step-by-step procedure to working dilution problems, and includes some practice problems at the end. Below is an applet to practice finding dilution factors, and also to determine how much water to add to achieve a given dilution. Most specimens have high enough numbers of microorganisms that the specimen has to be serially diluted to quantitate effectively. But for what it's worth, the dilution factor for 1 mL stock + 99 mL water is: amount transferred / total amount amount transferred / (amount transferred + amount water added) 1 / (1+99) 1/100 0.01. coli in nutrient broth all the way to soil samples and hamburger meat. It is a common practice to determine microbial counts for both liquid and solid specimens-suspensions of E.

#Microbiology dilution math how to

Understand how to quantify bacterial cells.