Mod 4 Test Flashcards
True or False: Growth media is best suited for distinguishing between two similar species of bacteria.
False
Growth media is designed to simply support (and not restrict) microbial growth.
A researcher is asked to determine which of two vials contains E coli and which contains salmonella. Knowing both are Gram-negative while only one of them is capable of fermenting lactose, which type of media would be best suited?
Differential media
What are the requirements of a fastidious microbe?
A fastidious microbe is an organism with complex growth requirements such that if absent it will not grow. Enriched medias thus contain these specific and essential nutrients required for the growth of a particular subset of microorganisms.
True or False: LB agar is classified as a non-selective, non-differential media.
True
LB agar is the most basic type of agar and like LB media supports the growth of virtually all microbes without restriction.
What is agar used for in microbiology?
Agar is used to create a solid, smooth surface on which microbes can grow.
Blood agar is which type of medium? Select all that apply.
Differential
Selective
Enriched
Selective and Differential
Differential
Enriched
Match the following hemolytic class with its description of activity.
- Alpha hemolysis A. No hemolytic activity
- Beta hemolysis B. Incomplete hemolytic
- Gamma hemolysis C. Complete hemolytic
1B
2C
3A
Columbia CNA agar is used to isolate:
Gram-Positive
CNA agar restricts Gram-Negative microbes therefore only Gram-Positive microbes will grow.
True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media.
False
Chocolate (cocoa) is never added to the media. The name is derived simply based on the color that actually comes from the presence of ‘cooked’ (lysed) red blood cells in the media.
An unknown microbe is streaked onto a MacConkey agar plate. After an overnight incubation at 37°C, growth is observed. Would a Gram stain be necessary? Why or why not?
No. A Gram stain would not be necessary, as only Gram-Negative microbes will grow on MacConkey agar.
In an attempt to detect the presence of the pathogenic strain of E. coli O157:H7, a researcher spread a culture onto a MacConkey agar with failed results. What type of agar should they (correctly) try next? Based upon what you know about the formulation of differential plates, explain why you chose this specific agar.
The microbe should be plated on SMAC (Sorbitol-MacConkey agar) as it is specifically formulated to detect O157:H7. Pathogenic E. coli (O157:H7) cannot ferment sorbitol while non-pathogenic E. coli can ferment both soribitol and lactose. Therefore, colonies that ferment (acidic conditions; non-pathogenic) can be differentiated from non-fermenters (neutral to basic conditions; pathogenic).
What is the Gram status (positive or negative) of microbes growing on Eosin Methylene Blue (EMB) agar plates?
Gram-Negative. EMB plates specifically restrict the growth of Gram-Positive bacteria.
Mannitol salt agar will turn what color in the presence of the pathogenic strain Staphylococcus aureus?
Yellow
Pathogenic Staph aureus will turn the agar from red to yellow.
What is the process of spreading a bacterial culture onto a petri dish called?
Plating
In order to visual individual colonies of bacteria would you culture your sample in a liquid media or on a solid (agar) media? Why?
Solid (agar) media. The primary advantage is that cells are held into place. When grown in a nutrient broth, bacterial cells can multiply but are free to move around in solution. When grown on agar within a petri dish the fixed in such as way as to form colonies.
True or False: The visualization of colonies on a petri dish represents bacterial cells that have multiplied ~2-3 times.
False
When an individual colony is visible on agar the bacterial cell has multiplied often a million times over.
True or False. The purpose of a quadrant streak is to produce individual colonies of a bacterial population.
True
The purpose of the quadrant streak is to generate individual colonies such that a single (pure) bacterial sample can be isolated.
Which of the following are correct in order to be considered a pure culture? Select all that apply.
Obtained by a serial dilution method
Obtained by a 4-phase dilution streak method
Multiple species
Free from contaminants
Obtained by pour plate serial dilution method
Long lifespan
Single organism
Obtained by a serial dilution method
Obtained by a 4-phase dilution streak method
Free from contaminants
Obtained by pour plate serial dilution method
Single organism
When performing a quadrant streak, the sample is spread across the plate in such as way as to form what?
A dilution gradient is formed. The resulting gradient should always contain within it the growth of individual colonies.
In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4?
P4 (Phase 4) would contain the lowest concentration of bacteria. The phases rank (from highest to lowest), P1 > P2 > P3 > P4.
True or False. When performing a dilution streak a new (or sterilized) loop must be used for each phase.
True
Failure to do so would prevent the establishment of a dilution gradient, as the same bacterial concentration would be spread across both phase regions.
What might a researcher do to encourage growth of a microbe with a long generation time that has already been streaked on an agar plate?
Increase incubation time
True or False. To restrict the growth of a pathogenic microbe a researcher might decrease an incubator from 37°C to 25°C.
True
Pathogenic strains of bacteria tend to grow faster than non-pathogenic strains at 37°C, so researchers may set incubators at 25°C to restrict its growth.
When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suites this need? Why?
MSA agar
LB media containing ampicillin and neomycin
MacConkey agar
Blood agar
Blood agar. All other options (A, B and C) are all forms of selective media, meaning they may potentially inhibit the growth of the unknown sample. Although blood agar is considered a differential media, it is, most importantly, a non-selective media. Given the alternatives, this is the best option.
