Lab

Question 1

Selective media

Answer 1

allows growth for some organisms, inhibits the growth of others

Question 2

Differential media

Answer 2

differentiates closely related organisms or groups of roganisms based on the organisms’s biochemical characteristics

Question 3

Is Sheep blood agar selective or differential?

Answer 3

DIFFERENTIAL (for lysing RBC)

Question 4

MacConkey Agar

• What is it selective for?
• Differentiates based on the ability to ___. And if a bacteria has the ability to _____ it will turn ___ color.

Answer 4

• selective for gram -
• differentiates based on ability to ferment lactose, if bacteria has ability to ferment lactose it will turn red.

Question 5

Mannitol Salt Agar (MSA)

• Selective for… because …
• Differential for ability to ____ and it will turn __

Answer 5

• Staphylococci
• ferment mannitol
  
  • pathogenic staphylococci can ferment and it will turn yellow (s. aureaus)

Question 6

S. epidermidis, corynebacteria, neisseria spp. haemophilus spp. and s aureaus can all be found in the…

Answer 6

nasal cavity

Question 7

Triple Sugar Iron (TSI)

• What sugars does this test for?
• What else does it test for?
• What color does glucose turn the media?

Answer 7

• TSI tests for sugar fermentation, sulfur reduction and CO2 simultaneously
• glucose turns the media yellow (decreases pH) with red slant (because once glucose is done pH on slant increases again and turns red)
• sucros and lactose turn the slant yellow all the way (stable decrease in pH)
• sulfur is black
• CO2 is cracks

Question 8

Motility Indole Ornithine Decarboxylase (MIO)

• What does motility look like?
• If the medium is ODC positive (meaning that the enzyme that decarboxylates Lornithine to putrescine is there) what happens to the pH and what color?
• What does indole test for? What color is indole positive? What is needed for this reaction?

Answer 8

• motility looks like growth extending away from a stab line
• the pH will go higher and the medium will turn purple
• indole tests for hte presence of tryptophanase an enzyme that converts tryptophan to indol. the color of positive is red and Kovacs reagent is necessary

Question 9

Citrate Utilization

• What is the indicator?
• What dose it mean if it is blue?

Answer 9

• bromothymol green is the pH indicator
• if it is blue (that means the pH has gone up) there is bacterial expression of citrate permease

Question 10

Urease

• What dose urease do?
• What color is urease positive?

Answer 10

• Urease hydrolyzes urea to produce amonia and CO2
• urease + is pink!