Exercise 18 - Quantitative and Semi-quantitative viable plate counts Flashcards
What can quantitative viable plate counts be used for?
-to enumerate the number of living bacteria in a unit volume
What does CFU’s stand for?
colony forming units
What is Semi-quantitative count used for?
to get a rough estimate of relative concentration of bacteria in an unknown volume
What was the objective for quantitative counts with the alfalfa sprouts?
- to enumerate the number of GRAM-NEGATIVE enteric organisms in 1 mil of alfalfa water
What does enteric mean?
intestinal
How is MacConkey agar a selective and differential media?
it is used in the selection of enteric bacteria while differentiating lactose-fermenters from non-lactose fermenters
What does lactose-fermenter (LF) mean and what’s an example?
- ferments lactose with the production of large quantities of acid
- e. coli is an example
What are two examples of non-lactose fermenters (NLF)?
- salmonella and shigella species
MacConkey Agar (MAC) contains what solution and what does it inhibit growth of?
- crystal violet solution
- inhibits gram positive, and non- enteric organisms
What pH indicator is added and what is detected?
pH indicator neutral red
- detects acid from lactose fermentation
Colonies that produce acid produce what color after the pH indicator is added?
- pink-red
Non- lactose fermenting organisms produce what color colonies after the pH indicator is added?
- beige - no obvious color change
Dilution definition.
- reducing the concentration of a substance by mixing it in a larger volume of diluent (such as water)
What type of exponent is associate with dilution?
a negative exponent
What is dilution factor?
the factor by which a substance has been diluted…the reciprocal of the dilution
