Quiz 10 Flashcards
How would you make a serial dilution with the following dilution factors, 10-1, 10-2, 10-3?
10-1 would be made by adding 1mL of the stock to 9mL of a peptone blank (solution A), 10-2 would be made by adding 1mL of solution A to 9mL blank (solution B), 10-3 would be made by adding 1mL of solution B to 9mL blank.
Define thermal death point
The lowest temperature needed to kill a population of microbes in 10 minutes.
Define thermal death time.
The time it takes to kill a population of microbes at a specified temperature.
Of the following–E. coli, S. aureus, and B. megaterium– which would you expect to be able to withstand the highest temperature for the longest period of time?
B. megaterium because it produces endospores.
What is the MPN test, and how was it used in the presumptive portion of the water quality test?
Most probable number test is use to find the MPN index which is then used to enumerate colonies of bacteria when you are expecting low microbial counts.
What was the specific medium used in the confirmed portion of the water quality test? How, specifically, is this medium both selective and differential?
EMB- Eosin Methylene Blue agar- is selective because it inhibits gram positive growth, differential because E. coli changes the pH which causes eosin to come out of solution giving colonies a metallic sheen (other gram negative rods appear a nucleated colonies).
