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

True

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?

Growth media

Selective media

Differential media

Non-selective and non-differential media

Differential media

What are the requirements of a fastdious microbe?

Fastidious microbes have complex growth requirements. If they are not met, they simply will not grow. Thus, these organisms are only able to grow on enriched media since this type of media has the specific and essential nutrients that they require to grow.

True or False: LB agar is classified as a selective, non-differential media.

False

LB agar is both non-selective and non-differential

What is agar used for in microbiology?

Agar allows us to have a solid/smooth surface that microbes can grow on.

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

Differential

Selective and differential

Enriched

Selective

Differential

Enriched

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

Alpha - Greenish-brown color (B)

Beta- Distinct zone of clearing (C)

Gamma - No change (A)

Columbia CNA agar is used to isolate:

Gram-Positive

Mycobacteria

Gram-Negative

Gram-Positive and Gram-Negative

Gram-Positive

True or False: Chocolate (cocoa) is not a component of Chocolate agar plates.

True

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?

A Gram stain would not be necessary because MacConkey agar plates are selective and can only grow Gram negative bacteria.

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?

Sorbitol-MacConkey agar should be tried next. This is because this type of agar let's us differentiate between the non-pathogenic and pathogenic (O157:H7) strain of E. coli. The non-pathogenic E. coli strain can ferment both sorbitol and lactose, whereas the pathogenic strain can only ferment lactose and not sorbitol. Sorbitol-MacConkey agar plates contain sorbitol instead of lactose like in standard MacConkey agar plates, which will let us differeniate between the pathogenic strain and non-pathogenic strain. If the colonies are non-pathogenic, the sorbitol with be fermented and acidic conditions produced. If the colonies are pathogenic O157:H7, the sorbitol will not be fermented and neutral/basic conditions will be seen.

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

Metallic green

Mannitol salt agar will turn what color in the presence of the pathogenic strain Staphylococcus aureus?

Yellow.

Pathogenic Staph aureus is able to ferment mannitol, and when it does so, the pH of the medium is lowered. This drop in pH causes the dye in the agar to change from red to yellow.

What is the process of spreading a bacterial culture onto a petri dish called?

Plating

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

When we use a petri dish, the bacterial cells are held in place, and thus the bacterial cells that multiply can form colonies that are easily detected. In a liquid culture, the bacterial cells can still multiply, but they are floating around in solution instead of being fixed in place.

True or False: The visualization of colonies on a petri dish represents bacterial cells that have often multiplied a million times over.

True

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

False

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

must not have external contaminants in it

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

Quadrant streak

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

P4

True of 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

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

A researcher may choose a 3-phase dilution streak instead of a 4-phase one, or instead of passing the sterile loop only once through the previous phase, more passings may be done

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 usually grow faster than non-pathogenic strains of bacteria at 37 degrees celsius, so lowering the temp can slow their growth

When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suits this need? Why?

1. MSA agar

2. LB media

3. MacConkey agar

4. Columbia CNA agar

LB media should first be used to expand the bacterial population. This is because this type of media is non-selective and non-differential, which allows it to expand all bacterial present. Since we do not know what is in the sample, if we go with the other types of media which are selective for certain strains and not others, we may be restricting the growth of the unknown sample.