micro quiz 3/14

Question 1

which family did today’s test help differentiate?

Answer 1

family Enterobacteriaceae

Question 2

Members of the Enterobacteriaceae are

Answer 2

Are Gram-negative
* Are rod shaped (bacilli)
* Live in the intestinal tracts of humans and animals
Can typically reduce nitrate
* Are facultative anaerobes
- Can ferment carbohydrates (like glucose)
* Can aerobically respire (have a functional citric acid cycle)

Question 3

Nitrate reduction test

Answer 3

Used to differentiate Enterobacteriaceae from Gram-negative rods that either do not reduce nitrate or reduce it beyond nitrite to N2 or other compounds (anaerobic)

Question 4

Nitrate reduction test indicators

Answer 4

1. Durham tube
2. Nitrate reagents A (sulfanilic acid) and B (α-naphthylamine)
3. Powdered zinc Red Color

Question 5

nitrate reduction test if red

Answer 5

positive, organism reduces nitrate to nitrite

Question 6

Citrate utilization test

Answer 6

This test tells us about the ability of organisms to use citrate as their sole carbon source and perform citrate fermentation
(blue positive)

Question 7

citrate utilization test carbon and nitrogen sources

Answer 7

Only carbon source: sodium citrate
* Only nitrogen source: ammonium phosphate

Question 8

a positive result (blue) on the citrate utilization test / Rxn

Answer 8

bacteria that survive the media and can utilize citrate to convert the ammonium phosphate to ammonia (NH3) and ammonium hydroxide (NH4OH) which both raise the pH of the agar.

Question 9

Malonate Utilization test

Answer 9

Malonate is similar to succinate and can competitively inhibit succinate
dehydrogenase  will lead to shut down of the cell
* UNLESS the cell can ferment or utilize malonate as it’s sole remaining carbon
source

Question 10

Malonate test results

Answer 10

Bromothymol blue (green at pH 6.9, blue at pH 7.6)
* Ferment glucose means lower pH (slightly yellow)
* Utilize malonate means raise pH (blue)

Question 11

Decarboxylation test

Answer 11

Amino acids can be catabolized by the removal of a carboxyl group (as
CO2)
Bromocresol purple (purple at pH 6.8 and above; yellow below pH 5.2)

Question 12

Decarboxylation test: possible amino acids

Answer 12

Lysine
* Ornithine
* Arginine

Question 13

Decarboxylation test why do we use mineral oil?

Answer 13

used to seal the medium from external oxygen
and promote fermentation

Question 14

Decarboxylation test

Answer 14

Initially, glucose fermentation will turn the medium yellow (accumulation of acid end
products)
The low pH and presence of specific amino acids induces organisms that encode the enzyme decarboxylase to express it and the action of the decarboxylase will turn the medium purple (accumulation of alkaline end products)

Question 15

Phenylalanine deaminase test

Answer 15

Used to differentiate the genera Morganella, Proteus, and Providencia
from other members of the Enterobacteriaceae

Question 16

Phenylalanine deaminase test reagent

Answer 16

Test reagent is Ferric Chloride (reacts with phenylpyruvic acid and turns a
dark green color)