SCSU BIO120 Lab Exam II(Lab instructor
Paul Campano's Microbiology Lab
(BIO120) course at Southern
Connecticut State University)
What is a pure culture? - correct answer ✔✔Cultures that contain only one type of organism and are
more suitable for the study of their cultural, morphological, and biochemical properties
What are the streak-plate and spread-plate methods? - correct answer ✔✔Methods used to isolate
similar cultures within a mixed culture
Describe the streak-plate method - correct answer ✔✔1. Open the dish and place a lapful of the culture
on the agar plate in area 1
2. Close the dish and flame the loop, wait 10 seconds
3. Turn the dish 90°, reopen the dish, and place the loop in area 1 to drag the culture to area 2
4. Close the dish and flame the loop, wait 10 seconds
5. Turn the dish 90°, reopen the dish, and place the loop in area 2 to drag the culture to area 3, close the
lid
6. Without reflaming the loop, turn the dish 90°, reopen the dish, and place the loop in area 3 to drag
the culture to area 4
What are special-purpose media used for? - correct answer ✔✔1. Isolation of bacterial types from a
mixed culture
2. Differentiation between similar groups of bacteria based upon the appearance of the colonies and
reactions with the medium
3. Listing names of bacteria in sanitary microbiology (water, sewage, food)
4. Determination of the amount of naturally occurring substances (antibiotics, vitamins)
5. Characterization and identification of bacteria and their ability to react with different mediums
, What is selective media? - correct answer ✔✔Media used to isolate specific groups of bacteria. They
inhibit the growth of one bacteria while permitting the growth of another
3 types of *selective media* - correct answer ✔✔1. Phenylethyl alcohol agar
2. Crystal violet agar
3. Sodium chloride agar
Phenylethyl alcohol agar - correct answer ✔✔Used to isolate most gram-positive organisms, partially
inhibits gram-negative organisms
Crystal violet agar - correct answer ✔✔Used to isolate most gram-negative organisms, inhibits most
gram-positive organisms
Sodium chloride agar - correct answer ✔✔Used to inhibit the growth of most organisms besides salt
loving (halophilic) organisms. Good for finding those in the Staphylococcus species
What is differential/selective media? - correct answer ✔✔Distinguishes among the morphology and
biochemically related groups of organisms. They produce a characteristic change in the appearance of
bacterial growth and/or the medium surrounding the colonies, which permits differentiation
3 types of *differential/selective media* - correct answer ✔✔1. Mannitol salt agar
2. MacConkey agar
3. Eosin-methylene blue agar (Levine)
Mannitol salt agar - correct answer ✔✔Contains a high salt concentration which inhibits the growth of
most organisms, except staphylococci. The differential function is that it contains is carbohydrate
mannitol which some staphylococci are capable of fermenting, and phenol red which is a pH indicator for
detecting acid produced by mannitol-fermenting staphylococci. Staphylococci that ferment appear
yellow while those that do not, produce no change in coloration
MacConkey agar - correct answer ✔✔Uses crystal violet to inhibit the growth of gram-positive organisms
and allow the isolation of gram-negative organisms. The differential function is that it contains the
carbohydrate lactose, bile salts, and the pH indicator, neutral red, permits differentiation of enteric
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