ex. 14

Question 1

Oxidase test
what do + and - results look like

Answer 1

The oxidase test is used to identify bacteria that produce cytochrome
c oxidase, an enzyme of the bacterial electron transport chain.

All bacteria that are oxidase positive are aerobic, and can use oxygen as
a terminal electron acceptor in respiration.

This does NOT mean that
they are strict aerobes

Question 2

nitrate reduction test
how to perform (what you do for week1 and week2,

Answer 2

1st week
* Obtain 3 nitrate broth tubes. Label with initials, class, media type, and organism.

• Inoculate 1 tube per species of bacteria given: Bacillus subtilis, Pseudomonas
  aeruginosa, and Lactococcus lactis.
• Incubate at 37°C

2nd week
1. Obtain your nitrate broth tubes inoculated the previous week.

2. Add 5 drops of nitrate reagent A (dimethyl-α-naphthylamine) and 5 drops of nitrate reagent B
   (sulfanilic acid) to each tube and to an uninoculated tube (only 1 control tube per table) and
   shake gently. A red color is positive for nitrate reduction to nitrite (+NO2-). Give it 5-10
   minutes and shake to see if turning pinkish to red.
3. If it does not turn red or pink, add a small scoop of zinc dust.
4. If it then turns red, then the organism is negative for nitrate reduction (-) because nitrate is still
   present in the broth. If there is no color change after the addition of zinc, the organism is
   positive for nitrate reduction to nitrogen gas (+N2).
5. Record your results in the Ex.13-14 data sheet tables.

Question 3

nitrate reduction test
what positive and negative results look like during/after the multiple steps of testing (after adding nitrate
A and B; after adding zinc)

Answer 3

2nd week

1st tube
color after reagents A and B: red
color after zinc: N/A
which was still present in the tube: nitrite NO2
nitrate reduction result: +NO2-

2nd tube
color after reagents A and B: yellow
color after zinc: pink
which was still present in the tube: nitrate
nitrate reduction result: negative

3rd tube
color after reagents A and B: yellow
color after zinc: yellow
which was still present in the tube: nitrogen gas
nitrate reduction result: N2

Question 4

nitrate reduction test
know which nitrogen-containing compound is remaining in tube to cause the color change reaction with the reagents
(nitrate, nitrite, or neither).

Answer 4

The results could be:

1. Negative, meaning nitrate still present in tube
2. + (NO2-) which means positive for nitrate reduction to nitrite (nitrite detected in
   tube)
3. +(N2) which means positive for nitrate reduction to nitrogen gas
   (neither nitrate nor nitrite detected in tube and bubble in Durham tube