Portage Learning Micro exam 4

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.

True or False: Growth media is best suited for distinguishing between two similar species of bacteria.

False

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.

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 are the requirements of fastidious microbe?

A fastidious microbe is an organisms with complex growth requirements such that if absent it will not grown. 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 selective, non-differential media.

False, 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?

Its used to create a solid and smooth surface on which microbes can grow

Blood agar is which type of medium? Select all that apply

Selective

Selective and Differential

Enriched

Differential

Enriched and Differential

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

1) B

2) C

3) A

Columbia CNA agar is most closely related to which media?

A. Trypticase Soy Agar

B. MacConkey Agar

C. Blood agar

D. EMB agar

C. Blood agar: CNA agar is similar to BAP as it is also enriched with blood and allows for differentiation based on hemolytic patterns.

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.

True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media.

False

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.

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

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 (SMAC) as it is specifically formulated to detect E. coli O157: H7. Pathogenic E. coli (O157:H7) cannot ferment sorbitol while non-pathogenic E. coli can ferment both sorbitol 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 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

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?

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. 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 support the formation and visualization of colonies.

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 over, often greater than a million, in order for the naked eye to resolve it.

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

True or False: The purpose of the quadrant streak is to expand bacterial population

False

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.

To be considered a pure culture, the sample (1) can be traced back to a single cell and (2)__________ ?

The culture must also be free from external contaminants. Simply put, a pure sample would never contain multiple bacterial species (ie) Strep and Staph

In what phase of a dilution streak would you expect to find the highest concentration of bacteria, P2 or P4?

P2

In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4?

P4

True or False. When performing a dilution streak a new (or sterilized) loop is not required for each phase as long as the bacterial culture is pure

False: A new or sterilized loop is absolutely required for each phase. Failure to do so would prevent the establishment of a dilution gradient, as the same bacterial concentration would be spread across both phase regions, regardless of whether or not the culture is pure

In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak?

A researcher may either (1) opt to perform only a 3-phase dilution streak or (2) pass the loop through the previous phase multiple times (as opposed to only once)

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

True or False; To restrict growth of a pathogenic microbe a researcher might decrease an incubator from 37 to 25C

True: (pathogenic strains of bacteria tend to grow faster than non-pathogenic strains at 37 degrees Celsius, so researchers may set incubators at 25 degrees Celsius 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?

1) MSA agar

2) LB media

3) MacConkey agar

4) Columbia CNA agar

LB Media. All other options (A, C and D) are all forms of selective media, meaning they may potentially inhibit the growth of the unknown sample. The culture should be first expanded and then place onto selective/differential agar plates

Columbia CNA agar is used to isolate:

Gram-positive

Mycobacteria

Gram-negative

Gram-positive and Gram-negative

Gram-positive (CNA agar restricts Gram-negative microbes therefore only Gram-positive microbes will grow

In Eosin Methylene Blue (EMB) agar, what color indicates the present of E. coli?

Metallic green sheen

Describe the primary advantage of using a petri dish over growth a liquid culture?

The primary advantage is that cells are held in 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 they are fixed in such a way as to form colonies

A dilution gradient is formed when carrying out what generalized plating strategy?

Quadrant Streak. The resulting gradient should always contain within it the growth of individual colonies

True or False. When performing a dilution streak a new (or sterilized) loop must be used for each phase

True