Topic 5: Isolation of Bacteria by Dilution Techniques

Pure culture

culture containing a single kind of microbe

Why are mixed cultures little use in studying microorganisms?

difficult to determine which organism is responsible for any observed activity

What is a pure culture?

culture containing a single kind of microbe

What type of culture is used to study microbes?

pure culture

True or False: Direct methods are used to separate bacteria.

False - indirect methods

Who in the 1870s, attempted to obtain pure cultures by performing serial dilutions until each of his containers theoretically contained one bacterium?

Joseph Lister

What are the three dilution methods for isolating bacteria?

streak plate, spread plate, pour plate

What is the most common isolation method?

streak plate

What methods are quantitative techniques that allow determination of number of bacteria in a sample?

spread plate and pour plate

How many colonies must be present on a plate to determine the number of bacteria in an original sample?

25-250

What equation is used to calculate the number of bacteria in an original sample?

colony-forming units per ml = number of colonies / (dilution X amount plated)