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Microbiology > Lab Final Exam > Flashcards

Lab Final Exam Flashcards

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Biology 101 flashcards
1
Q

T/F:

Tiny earth searches for antibiotic-resistant bacteria in the soil because as soil erodes, antibiotic-resistant bacteria can end up in our waterways.

A

FALSE

Antibiotic-producing bacteria

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2
Q

T/F:

TSA with cyclohexamide is a differential medium for antibiotic producers.

A

FALSE

Selective medium (against fungi)

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3
Q

T/F:

To make a ten-fold dilution, you transfer 100uL of stock to 900 uL of water.

A

TRUE

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4
Q

T/F:

The serial dilution plate grew ALL bacteria in your soil sample.

A

FALSE

Not all bacteria can be grown in culture (only ~30% can)

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5
Q

T/F:

Antibiotic producing bacteria are resistant to all antibiotics.

A

FALSE

Only resistant to the antibiotic it produces.

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6
Q

T/F:

After you quadrant streak a plate, you should put it in the fridge.

A

FALSE

Grow in incubator

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7
Q

Good/Bad Choice:

After observing the growth of your patch plate, you want to keep the plate to use it again next week, so you put it in the incubator.

A

BAD CHOICE

Put in refridgerator

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8
Q

Convert 1.5 cm to mm

Convert 0.7 cm to mm

A

15 mm

7 mm

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9
Q

Draw a ten-fold serial dilution through 10^-5.

How much is transferred each time?

How many tubes?

How much diluent (water) is in each tube?

A

1 mL transferred each time (100 uL)

5 tubes (not including stock solution)

9 mL in each tube (900 uL)

See drawn picture on iPad

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10
Q

Design a protocol to test whether bacteria isolated from your garden produce any antibiotic compounds capable of inhibiting the growth of E. coli.

How would you interpret the results?

Why would you want to sample soil from a vibrant garden?

A

Protocol:
1. Harvest soil sample (aseptic technique)
2. Culture soil sample (serial dilutions)
3. Pick diverse colonies (patch plate)
4. Screen colonies for ability to inhibit E. coli growth (patch plate with E. coli lawn; observe clearing)
5. Isolate pure cultures

Results:
Clearing = zone of inhibition
- Indicates inhibition of E. coli growth
- Potential antibiotic-producer (antimicrobial activity)

More vegetation = more microbial diversity

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11
Q

Interpret chart about Kirby Bauer results.

Which drug should be used for treatment?

What can you conclude about Chloramphenicol?

A

Kanamycin should be used for treatment (S - sensitive)

Chloramphenicol must be used in combination with another antibiotic to clear infection (I - intermediate)

See iPad drawing.

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12
Q

Biochemical Tests

MSA

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Selective agent = 7.5% NaCl
- Selects for Staph
- Inhibits G-

Indicator = phenol red
- Differentiation of S. aureus from other Staphylococcus species

Results:
- Growth = halotolerant
- Yellow = mannitol fermentation
- No color change (red) = no fermentation

Mannitol Salt Agar

Selective & differential

G+ media

Substrate = mannitol

Good growth + yellow = possible S. aureus
Good growth + red = Staph other than S. aureus

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13
Q

Biochemical Tests

BEA

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Selective agent = oxgall (bile)
- Separates Group D Streptococci from other Strep spp.
- Inhibits G-

Indicator = ferric citrate
- Oxidized iron

Results:
- Black precipitate = + (esculin hydrolysed in presence of bile)
- No blackening = -

Bile Esculin Agar

Selective, & differential

Undefined, G+ medium

Other ingredients:
- Beef extract (nutrients & energy)
- Digest of gelatin (nutrients & energy)
- Esculin (horse chestnut tree bark extract)

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14
Q

Biochemical Tests

EMB

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Selective agent = eosin & methylene blue dyes
- Inhibits G+

Indicators = eosin & methylene blue dyes
- Isolation of fecal coliforms (lactose fermenters)

Results:
- Dark purple/black = lactose fermentation
- Pink/mucoid growth = lactose fermentation
- Metallic = LOTS of fermentation
- Colorless = no fermentation

Eosin-Methylene Blue Agar

Selective & differential

G- media

Substrate = lactose

E. coli = metallic green

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15
Q

Biochemical Tests

HEA

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Selective agent = bile salts
- Inhibits G+

Indicators:
1. Sodium thiosulfate (reduces sulfur to H2S)
2. Bromothymol blue & acid fuschin dyes (pH change)

Results:
- Blue/green = no sugar fermentation (Shigella)
- Blue/green + black precipitate = sugar fermentation, sulfur reduction (Salmonella)
- Pink/orange grow = sugar fermentation

Hektoen Enteric Agar

Selective & differential

Gram- media

Substrates:
- Lactose
- Sucrose
- Salicin

Used to isolate/differentiate Salmonella & Shigella from other enterics in pt stool samples or dairy/poultry

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16
Q

Biochemical Tests

MAC

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Selective agents = bile salts & crystal violet
- Inhibit G+

Indicator = neutral red dye
- Isolate & differentiate Enterobacteriaceae based on ability to ferment lactose

Results:
- Colorless = no fermentation (pH > 6.8)
- Pink/red = lactose fermentation (pH < 6.8)

MacConkey Agar

Selective & differential

G-media

Substrate = lactose

17
Q

Biochemical Tests

CNA

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Selective agents:
1. Colistin (antibiotic): G- membrane integrity
2. Nalidixic Acid (antibiotic): DNA replication

Indicator: sheep blood
- Differentiation based on hemolysis
- Isolates Staphylococci, Streptococci, & Enterococci from clinical specimens

Results:
- Alpha hemolysis = partial
- Beta hemolysis = complete
- Gamma hemolysis = none

Columbia CNA Agar

Selective & differential

G+ media

Yeast extract provides B vitamins

18
Q

Biochemical Tests

TSIA

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Indicators:
- Phenol red (pH)
- Ferrous sulfate (H2S)

Results:
A/A = yellow slant & butt
- Fermentation

K/A = red slant & yellow butt
- Glucose fermentation
- Proteins catabolized aerobically with alkaline products (reversion)

K/K = red slant & butt
- NO fermentation
- Peptone catabolized aerobically & anaerobically
- NOT from Enterobacteriaceae

K/NC = red slant & no change in butt
- NO fermentation
- Peptone catabolized aerobically
- NOT from Enterobacteriaceae

NC/NC = no change in slant/butt
- Organism growing slowly or not at all
- NOT Enterobacteriaceae

H2S = black precipitate in agar
- Sulfur reduction
- Acid condition (from fermentation of lactose)

G = cracks/lifting in agar
- Gas production

Triple Sugar Iron Agar or Kliger Iron Agar (KIA)

Differential ONLY
- Differentiate Enterobacteriaceae from other G- rods

Sugars:
- Glucose (0.1%)
- Lactose (1%)
- Sucrose (1%)

19
Q

Biochemical Tests

SIM

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Indicators:
1. Ferrous ammonium sulfate
2. Kovac’s reagent (DMAB)

Results:
- Black precipitate = sulfur reduction
- Red/pink = indole production
- Turbidity away from stab = motile

Sulfur reduction, Indole production, Motility

Differential ONLY
- ID of Enteric bacteria species

Reduced agar concentration (0.5%) makes motility possible

Indole produced if bacteria has tryptophanase

Black precipitate = ferric sulfide (H2S combied with indicator)

20
Q

Biochemical Tests

PRSBs

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Indicator = phenol red (pH)
- Differentiates Enterobacteriaceae from other G- rods
- Differentiates G+ fermenters

Results:
A/G = yellow broth & bubbles
- Sugar fermented with acid & gas products

A/- = yellow broth & no bubbles
- Sugar fermented with acid products ONLY

-/- = red broth & no bubbles
- NO fermentation

K = pink broth (no bubbles)
- NO sugar fermentation
- Peptone degraded with alkaline end products

Phenol Red Sugar Broths

Differential ONLY

Durham tube - collects gas from fermentation

4 carbohydrate versions:
1. Glucose (green cap)
2. Sucrose (yellow cap)
3. Lactose (red cap)
4. Mannitol (white cap)

21
Q

Biochemical Tests

Citrate

  1. Selective (how/what organisms)?
  2. Differential (how/what organisms)?
  3. Result interpretation (color/meaning)
A

Indicator = bromothymol blue (pH)
- Differentiates based on which organism can use citrate as sole carbon source

Results:
- Blue = citrate utilization + (alkaline byproduct)

Differential ONLY
- Citrate permease allows citrate into cell for citrate catabolism/fermentation

Defined media

Microbiology (15 decks)

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