GMU MICRO BIO 306 FINAL

You have a 5M stock solution and want to dilute it down to a 0.2M solution that has a final volume of 25mL. (a) how much stock solution would you need to add? (b) how much diluent do you need to add to the solution to bring the total volume up to 25 mL?

(a) C1V1 = C2V2

(5)V1 = (0.2)(25mL)

V1 = 1mL

(b) 25 - 1mL = 24mL

Explain the difference between chemically defined media and complex media

- chemically defined is composed of chemicals

- complex is composed of many components (potentially chemicals in addition to other substances)

A gram positive stained organism is what color, and is stained that color due to?

(a) purple / peptidoglycan layer

(b) purple / lipopolysaccharide layer (LPS)

(c) pink / peptidoglycan layer

(d) pink / lipopolysaccharide layer (LPS)

(a) purple / peptidoglycan layer

What would be a simple way to separate two different bacterial strains from a broth solution?

Plate the mixed culture (streak plate)

If you want to make a 40% NaCl solution how many grams of NaCl would you add to 200mL?

g/mL = __%

g/200mL = 40%

g = 80g

True or false: bacterial culture media must be sterilized prior to use

true

Which class of organisms would completely lyse red blood cells and leave a completely clear zone around itself in a blood agar plate?

(a) alpha hemolytic

(b) beta hemolytic

(c) gamma hemolytic

(b) beta hemolytic

Define selective media and differential media

- selective media: only certain bacteria can grow on it

- differential media: bacteria shows distinction by color changes or chemical changes

What does it mean to have a "pure culture"? Name one way you can test to see if your culture is pure.

"pure culture" means the culture contains one bacterium that has not been contaminated with an outside bacteria. By completing a streak plate, one can determine if a culture is pure based on if there is only one type of colony growing on the agar or not

What is the difference between gram positive and gram negative cells?

- gram + have a peptidoglycan layer that stains blue/purple

- gram - doesn't have a peptidoglycan layer so it stains pink/red

True or false: gram positive cells retain the safranin, causing them to turn red while gram negative cells are a blue/purple color during staining

false

What structure are we staining for with a negative stain?

capsules

What property are we staining for with an acid-fast stain?

waxy bilayer around cell that impacts virulence

What are endospores? How are they formed?

- endospores are highly durable, dehydrated cells with thick walls and additional layers, formed internal to the bacterial cell membrane

- only produced by gram positive bacteria

- formed when bacterial cells stop growing, formed within vegetative cells

True or false: streaming is the river-like flow of masses of cells due to currents in an aqueous media

true

Why are mycobacterium smegmatis and bacillus cereus used as false positives for endospores and acid fast stains?

both are resistant to decolorization

If 5mL of sample is dliuted into 15mL of diluent, what is the dilution factor?

5 + 15 = 20

5/20 = 1/4 = .25

Name one way to make a 1:50 dilution

1 mL into 49mL

2mL into 98mL...etc

If you counted 47 colonies on your 10^-4 plate after incubating overnight, what is your CFU/mL?

47x10^4 CFU/mL

Explain the difference between conjugation and transformation.

- conjugation is the sharing or DNA from cell to cel

- transformation is the uptake of naked DNA

True or false: an auxotroph does not require additional nutritional supplements

false

Choose one: cells with chemically altered cell walls and are capable of being transformed are called (artificial/competent) cells.

competent

A P200 reads as below. What volume is this?

1

5

1

151 microliters

True or false: during conjugation, DNA is transferred by cell-to-cell contact via a pilus

true

Why do we heat fix slides?

heat fixation prevents the bacteria from washing off the slide during the staining procedure

Define alpha hemolytic, beta hemolytic, and gamma hemolytic

(a) alpha hemolytic: some breakdown of red blood cells

(b) beta hemolytic: complete breakdown of red blood cells, clearing of red

(c) gamma hemolytic: no red blood cel breakdown

What is a negative stain?

A negative stain is one that stains the background rather than the cell or its structures. The organisms stand out against a dark-colored background. The negative stain will show if an organism has a capsule or not.

What are the different categories or oxygen requirements?

aerobic: require oxygen for their metabolism

facultatives: can grow with or without oxygen

microaerophiles: prefer low oxygen tensions

obligate anaerobes: unable to grow in the presence of dissolved oxygen

What is the formula to determine a solution? Provide an example.

Dilution = volume of sample/volume of sample + volume of diluent

1.0mL of sample is mixed with 9.0mL of diluent, the dilution is 1/1+9, or 1/10

You dilute your bacteriophage for plating 10-6. You mix 0.1ml of bacteriophage dilution with 0.3 ml of bacteria and the next day you count your plaques. You have 55 plaques. What is the total number of pfu/ml of the bacteriophage stock? Show your work.

55x10^7