MIDTERM 2 Hydrogen Sulfide Test

Question 1

What can be said about an organism with the ability to produce hydrogen sulfide?

Answer 1

It helps identify facultative anaerobic gram-negative rods

Question 2

True or false: aerobes can produce hydrogen sulfide too

Answer 2

True

Question 3

Why does the H2S production test favor fermenters?

Answer 3

because it requires a low pH

Question 4

Microbes can produce Hydrogen sulfide in 2 ways. what are they?

Answer 4

1. As end product of cystein or methionine metabolism. The -SH group is removed from the carbon backbone and is reduced to produce hydrogen sulfide
2. Through process of anaerobic respiration. sulfate or thiosulfate is used as an alternate electron acceptor

Question 5

Why isnt odor used as a diagnostic feature of Hydrogen Sulfide?

Answer 5

Because inhaling the gas can be very toxic

Question 6

Why cant you use the durham tube to test for Hydrogen sulfide Gas?

Answer 6

because the gas is VERY SOLUBLE in water

Question 7

What is used for the detection of hydrogen sulfide?

Answer 7

Medium containing Fe2+ ions that will allow the Hydrogen sulfide to produce a black ferrous sulfide precipitate.

Question 8

What media is used to test Hydrogen sulfide?

Answer 8

Kligler iron Agar

Question 9

What does Kligler iron agar contain?

Answer 9

1. It contains peptone
2. and Thiosulfate
3. Glucose
4. Lactose
5. Phenol red

Question 10

What is the significance of peptone in the KIA media?

Answer 10

it is rich in amino acids such as cysteine and methionine

Question 11

What is the significance of Thiosulfate in the KIA media?

Answer 11

its an additional source of sulfur and an alternative terminal electron acceptor

Question 12

Which sugar ( glucose or Lactose ) is found in higher quantity in the KIA media ?

Answer 12

Lactose is found in much higher quantity

Question 13

explain the priority of bioorganic molecules a microorganism uses as a source of energy?

Answer 13

Weither they are Aerobic or Anaerobic, they use

1. Glucose first
2. peptone second ( if they can use lactose, theyll use it next)

Question 14

If organism uses Glucose Aerobically, What happens to the KIA medium and why?

Answer 14

Theres little to no color change in the first 24 hours because the by-products of glucose catabolism do not significantly alter the pH

Question 15

If organism uses Glucose via fermentation, What happens to the KIA medium and why?

Answer 15

The acid produced drops the pH and causes the phenol red to turn yellow. a yellow butt and a yellow slantwould appear after 24 hours.

Question 16

How is there a yellow slant in the KIA medium if an organism uses glucose via fermentation

Answer 16

Upward diffusion of acid from the anaerobic butt

Question 17

Explain what can happen once glucose is exhausted from the KIA medium

Answer 17

the organism will ferment lactose. Since lactose is in such a great amount, the tube will remain yellow at the 48 hour observation period.

Question 18

explain what can happen once glucose is exhausted from the kia medium but the organism cant use lactose

Answer 18

Breakdown of the amino acids in peptone occurs
Ammonia is released as a by product
Ammonia shifts pH to a more alkaline value
This changes color of the phenol red to a reddish pink

Question 19

What can be determined if the slant of the KIA is pinkish red?

Answer 19

organism is capable of aerobic peptone utilization only

Question 20

What can be determined if both the slant and the butt of the KIA medium is red

Answer 20

Organism is capable of anaerobic peptone utilization

Question 21

What can be said about the black precipitate of ferrous sulfide in the medium?

Answer 21

1. forms under acidic conditions

2. indicates fermentation is occurring even if it obscures butt and slant

Question 22

How dos KIA medium turn black?

Answer 22

When hydrogen sulfide is produced because ferrous iron is present in the medium