Exam 4 Flashcards
To be considered a pure culture, the sample (1) ______(2)__________ ?
can be traced back to a single cell and is free of outside contaminants.
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. Because the liquid media is where bacterial cells can multiply but are able to move around in the solution; whereas, bacteria plated on a solid agar are fixed and it supports the formation and visualization of colonies.
True or False: The purpose of the quadrant streak is to expand bacterial population
False
What are the requirements of fastidious microbe?
Enriched media is used to grow fastidious microorganisms. Fastidious microorganisms are organisms with complex growth requirements, and if absent they will not grow. They contain essential nutrients that are required to grow microorganisms.
True or False: LB agar is classified as a selective, non-differential media
False, LB agar is the most basic type of agar
Match the following hemolytic class with its description of activity.
1. Alpha hemolysis
2. Beta hemolysis
3. Gamma hemolysis
A. No change
B. Greenish-brown color
C. Distinct zone of clearing
- B
- C
- A
A researcher is studying a strain of E coli, currently growing on a MacConkey plate. However, the researcher cant remember if E coli is gram positive or gram negative. Would a gram stain be necessary to confirm? Why or Why not?
No because only gram negative microbes will grow on a MacConkey plate. Thus E coli is gram negative.
What is the Gram status (positive or negative) of microbes growing on Eosin Methylene Blue (EMB) agar plates?
Gram-negative, EMB plates restricts growth of gram positive bacteria
Which type of agar media is best suited to support the growth of Staphylococcus?
Columbia CNA agar
Blood agar
Chocolate agar
Mannitol salt agar
MacConkey agar
Mannitol Salt Agar
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?
1) MSA agar
2) LB media
3) MacConkey agar
4) Columbia CNA agar
LB media. The other forms of media are selective media, which means they could potentialy inhibit the growth of the unknown bacterial sample. The culture first needs to be expanded then placed onto a selective/differential plate.
True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media
False
The polysaccharide-based hardening agent added to LB media to produce LB agar is derived from what?
Seaweed Extract
Describe the primary advantage of using a petri dish over growing a liquid culture?
When using a petri dish you can observe the growth of a sample in a specified region. The primary advantage is that cells are held into place. When grown in a nutrient broth, bacteria cells can multiply and are free to move around in solution. When grown on agar within a petri dish fixed in such a way to form colonies.
True or False; To restrict growth of a pathogenic microbe a researcher might decrease an incubator from 37 to 25C
True
In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4?
P4
A researcher is asked to determine if a sample contains Neisseria meningitides. Knowing Neisseria meningitides is slow growing and other foreign microbes may also be present in the culture, which type of media would be best suited?
Growth Media
Selective Media
Selective and Differential Media
Differential Media
Selective Media-if additional foreign microbes may be present in your sample and you know Neisseria is slow growing you want to restrict unwanted microbes
When performing a quadrant streak, the sample is spread across the plate in such as way as to form what?
To establish a dilution gradient. The gradient should always contain within it the growth of individual colonies.
True or False: Chocolate (cocoa) is not a component of Chocolate agar plates
True; the name is derived simply based on the color that actually comes from the presence of cooked lysed
Columbia CNA is used to isolate:
Gram-Positive bacteria
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?
1) MSA agar
2) LB media containing ampicillin and neomycin
3) MacConkey agar
4) Blood agar
Blood agar. All other options 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.
True or False: Growth media is best suited for distinguishing between two similar species of bacteria
False
In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak?
A researcher could either choose to involve fewer phases (3 phases instead of 4) or pass the loop through the previous phase numerous times (instead of only once).
Match the following hemolytic class with its description of activity.
1) Alpha hemolysis
2) Beta hemolysis
3) Gamma hemolysis
A. No hemolytic activity
B. Incomplete hemolytic activity
C. Complete hemolytic activity
B. Incomplete hemolytic
C. Complete hemolytic
A. No hemolytic activity
True or False: The visualization of colonies on a petri dish represents bacterial cells that have often multiplied a million times over.
True; to form a bacterial colony the initial cells must have multiplied many times.
Blood agar is which type of medium? Select all that apply
Selective
Selective and Differential
Enriched
Differential
Enriched and Differential
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
In what phase of a dilution streak would you expect to find the highest concentration of bacteria, P2 or P4?
P2
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? Why?
The microbe should be plated on Sorbitol-MacConkey agar because it is formulated to detect O157:H7. Pathogenic E. Coli is unable to ferment sorbitol while non-pathogenic E. Coli is able to ferment both soribitol and lactose. The colonies that are able to ferment can be differentiated from non-fermenters.
The number phase (3 vs 4) and/or the number of times a loop passes through a
Either deviation is acceptable in practice provided the resulting gradient contains within the growth of individual colonies-if not, the experiment must be repeated.
What is the process of spreading a bacterial culture onto a petri dish?
Plating
A researcher is asked to determine which 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.
Growth Media
Differential Media
Selective Media
Selective and Differential Meida
Differential Media
What is agar used for in microbiology?
Its used to create a solid and smooth surface so microbes can grow on
True or False: Differential media is best suited for distinguishing between two similar species of bacteria
True: growth media does not contain restrictive factors, while selective media is best used to encourage the growth of one microbe
Mannitrol salt agar will turn what color in the presence of the pathogenic strain staphylococcus aureus
Yellow
True or False: Pathogenic strains of bacteria tend to grow slower than normal non-pathogenic bacterial strains.
False; pathogenic strains of bacteria tend to grow faster
Columbia CNA agar is most closely related to which media?
Trypticase Soy Agar
MacConkey Agar
Blood agar
EMB agar
Blood Agar
An unknown microbe is streaked onto a MacConkey agar plate. After an overnight incubation of 37C, growth is observed. Would a gram stain be necessary? Why or why not?
No because a gram stain would not be necessary, since only gram negative microbes will grow on MacConkey agar
True or False: When performing a dilution streak a new (or sterilized) loop must be used for each phase.
True
