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Microbiology Lab > Biochemical activities of microorganisms > Flashcards

Biochemical activities of microorganisms Flashcards

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Biology 101 flashcards
1
Q

enteric bacteria (Enterobacteriaceae)

A

-diverse group of bacteria found in the gastrointestinal tract
-can be normal flora, opportunistic or pathogenic
-they are facultative anaerobic gram-negative bacilli
-

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2
Q

Triple Sugar Iron test (TSI)

A

-performed with enteric bacteria to determine carbohydrate fermentation

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3
Q

Fermentation

A

-an anaerobic process which involves the degradation of sugars to various end products like acid, alcohols, and gas

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4
Q

What sugars do the Triple Sugar Iron test contain

A

1.Glucose
2. Lactose
3. Sucrose

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5
Q

What is the pH indicator in the Triple Sugar Iron test?

A

phenol red
-turns yellow in the presence of acid (pH below 6.8)

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6
Q

What is something else the Triple Sugar Iron test detects?

A

-detects formation of gasses, hydrogen and carbon dioxide are detected by observing cracks or bubbles in the medium
-hydrogen sulfide gas is detected by incorporating ferrous sulfate which produces a black precipitate in the presence of hydrogen sulfide

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7
Q

TSI: Appearance of red slant/red deep

A

no sugars fermented

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8
Q

TSI: Appearance of red slant/ yellow deep

A

-only glucose is fermented (some acid produced)
- acid will begin to build up in the base of the tube causing phenol red to turn yellow

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9
Q

TSI: Appearance of yellow slant/ deep

A

glucose fermented, and lactose and/or sucrose are fermented (a lot of acid is produced)
– acid will begin to build up in the base of the tube causing phenol red to turn yellow in the base and slant

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10
Q

TSI: Appearance of bubbles or cracks

A

-sometimes the media is pushed up from the bottom of the tube
-CO2 or H gas production

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11
Q

TSI: Appearance of a black precipitate

A

-can be found in the deep, but also extend to the slant
-hydrogen sulfide (H2S) production

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12
Q

What cultures did we used that need the TSI test to differentiate them?

A
  • pseudomonas, Serratia, E.coli, and Proteus
    -they all are gram negative and rod shaped
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13
Q

TSI test on E.coli

A

-ferment glucose, lactose, and sucrose
-produces CO2 and H gas
- no H2S production
* deep yellow and slant yellow

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14
Q

TSI test on Pseudomonas

A
  • no sugar fermentation
    -no gas production
    -no H2S production
  • deep red and slant red
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15
Q

TSI test on Serratia

A

-ferment glucose only
- no gas production
-no H2S production
* deep yellow, red slant

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16
Q

TSI test on Proteus

A
  • ferments sucrose only
  • sometimes CO2 or H gas
    -produces H2S production
  • deep yellow, red slant
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17
Q

citrate utilization

A

-determines the capability of an organism to utilize sodium citrate as the sole source of carbon

18
Q

What are the chemicals used in citrate utilization test

A
  1. citrate as the sole carbon source
  2. Inorganic ammonium salts (NH4H2PO4) as the only source of nitrogen
  3. Bromothymol blue = pH indicator will turn blue if pH over 7.6 (original color is green)
19
Q

How does the citrate utilization test work

A

-bacteria metabolizes or uses citrate as a carbon source. This metabolic reaction causes ammonium salts to break down and form ammonia as a by product in the media
-the ammonia increases and causing the pH to increase (more basic), so the media changes from green to blue

20
Q

Exceptions to the citrate test

A

there are rare citrate positive organisms that can utilize citrate substrate without producing enough alkaline reaction to change the pH indicator, so growth on a slant without a blue color is needed

21
Q

What bacteria was used in the citrate test

A

E.coli and Proteus
-both are gram negative and rod shaped

22
Q

Citrate use test: E.Coli results

A

-does not use citrate as a carbon source
-green color

23
Q

Citrate use test: Proteus results

A

use citrate as a carbon source
-blue color

24
Q

catalase test

A

-organisms capable of producing the enzyme catalase can rapidly degrade hydrogen peroxide (H2O2) into free water and oxygen
-can be determined by adding hydrogen peroxide to bacteria on a glass slide
-if catalase is present bubbling occurs which is free oxygen escaping

25
Q

What is the catalase test used to distinguish between?

A

-often used to distinguish between gram positive cocci staphylococcus from streptococcus

26
Q

why do microorganism produce catalase enzymes?

A

-to neutralize the harmful effects of oxygen metabolites such as hydrogen peroxide (H2O2)
-H2O2 steals electrons from structures in the cell wall causing it to destabilize and destroy the cell wall
-while catalase will neutralize the hydrogen peroxide and protect the cell wall

27
Q

Catalase test reaction

A

2 H202 —> (catalase)—> 2 H2O + O2

28
Q

What bacteria do we used for the catalase test

A

-streptococcus and staphylococcus

29
Q

Catalase test: streptococcus result

A

no catalase

30
Q

Catalase test: staphyococcus result

A

catalase

31
Q

oxidase test

A

-determines if the species produces the enzyme cytochrome oxidase
-the oxidase reagent contains a chromogenic reducing agent , if cytochrome oxidase is present in the bacteria it will take electrons from the chromogenic reducing agent
-takes electors from the donor molecule and gives it to oxygen
-the chromogenic reducing agent is oxidized and turns blue/black color
- in a clinical lab this test can be used to distinguish Enterobacteriaceae from non- Enterobacteriaceae

32
Q

What does cytochrome oxidase do

A

-participates in the electron transport by transferring electrons from a donor molecule to oxygen

33
Q

What bacteria did we use for the oxidase test

A

E.coli and Pseudomonas
-both are gram negative and rod shaped

34
Q

Oxidase test: E.Coli results

A

no oxidase

35
Q

Oxidase test: Pseudomonas results

A

oxidase

36
Q

oxidase test reaction

A

2 reduced cytochrome c + 2H+ + 1/2 o2 –> (cytochrome oxidase)–> 2 oxidized cytochrome c + H2O
-cytochrome c is the terminal enzyme in the electron transfer chain, the enzyme which reduces molecular oxygen to water to complete the last link in the chain of aerobic respiration

37
Q

citrate slant: growth and blue

A

use citrate of carbon source exclusively

38
Q

citrate slant: green

A

does not exclusively use citrate as the carbon source

39
Q

catalase test: no bubbling

A

no catalase present

40
Q

catalase test: bubbling

A

catalase present

41
Q

oxidase test: reagent color change to blue/black

A

cytochrome oxidase present

42
Q

oxidase test: no color change in reagent

A

cytochrome oxidase not present

Microbiology Lab (14 decks)

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