Microbio Lab Quiz 6 (25-29)

Blood Agar: Differential or Selective

Differential

Beta-hemolysis

complete destruction of RBCs and hemoglobin

What does B-hemolysis look like on the media

clearing around the colonies

alpha-hemolysis

partial destruction of RBCs

What does a-hemolysis look like on the media

olive-greenish discoloration around colonies

y-hemolysis

non-hemolytic

Phenol Red Lactose Fermentation Broth: Differential or Selective

Differential

What is the Phenol Red Broth used to determine

if the added carbohydrate is fermented or not

Phenol Red as a pH indicator will turn the broth (1) below pH 6.8, (2) above pH 7.4, and (3) between pH 6.8-7.4

1) yellow

2) pink/magenta

3) red

within the broth, the inverted Durham tube determines what

gas production

For Phenol Red Broth: yellow broth, bubble in tube

fermentation of carbohydrate with acid and gas end products

For Phenol Red Broth: yellow broth, no bubble in tube

fermentation of carbohydrate with acid end products but no gas produced

For Phenol Red Broth: red broth, no bubble in tube

no fermentation of carbohydrate or gas production

what is the sole carbon source in the Citrate Utilization test

sodium citrate

what is the sole nitrate source in the Citrate Utilization test

ammonium

Only organisms with these enzymes can survive in the Citrate Utilization test

citrate lyase and citrate permease

citrate lyase

hydrolyzes citrate into oxaloacetate and acetate

citrate permease

transports oxaloacetate into the cell to perform citrate fermentation

What is the purpose of the Citrate Utilization Test

to differentiate Enterobacteriaceae based on ability to use citrate as sole carbon source and perfrom citrate fermentation

Bacteria that can utilize citrate also convert ammonium phosphate to ammonia and ammonium hydroxide resulting in a pH

increase

pH indicator is Citrate Utilization test

bromothymol blue

below pH 6.9 the citrate agar will be the color (1)

above pH 7.6 the citrate agar will be the color (2)

1) green

2) blue

Even if the medium does not turn blue, growth on the Citrate Agar is considered a

positive reaction

urea hydrolysis is used to differentiate organisms that contain the enzyme

Urease

The Urease Test contains strong buffers that prevent the alkalinization of medium by all but which organisms

rapid urease-positive organisms

What is the pH indicator used in the Urease Test

Phenol Red

If the Urease Test medium is yellow or orange, that indicates a

urease-negative organism

If the Urease Test medium is red or pink in less than 24 hrs, that indicates a 

urease-positive organism

How is the Motility Agar inoculated

with a straight transfer needle

What is the purpose of TCC in the motility agar

used as an electron acceptor, turns Red when reduced, added to make interpretation easier

Positive result for motility

red TCC is seen radiating outward from central stab

negative result for motility

red TCC is only along the stab line