What two procedures should you routinely carry out to verify the purity of your working stock in a lab?

Question

While using an unknown microorganism sample, you may not be sure your sample is purely one kind of microorganism.

Answer 1

To determine if a microorganism stock is clean

1. Spread a dilution series on a solid agar plate and place at appropriate temperature - more than one shape? color? texture? = contaminito

2. Spread a dilution series on a permissive plate - correct sugar or antibiotic and replica plate onto a non-permissive plate - something that grows on both? = contaminito

3. bonus - grow in solution using correct salt, sugar and all, at correct temperature and at a different temp and see how fast your cells grow by change in density (eg. O.D. 600 nm) - not growing as fast as expected = mixed culture - go to #1 and streak out solution to isolate the correct organism.

hope this helps

Answer 2

subculture a single colony every day or two. use proper streaking technique to make sure your colonies are well-isolated.

use selective media in your subculture, such as CNA agar for gram positives, or MacConkey's agar for gram negatives. check to make sure these daughter colonies look like the original one.