Biochemical activities of microorganisms Flashcards
(42 cards)
enteric bacteria (Enterobacteriaceae)
-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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Triple Sugar Iron test (TSI)
-performed with enteric bacteria to determine carbohydrate fermentation
Fermentation
-an anaerobic process which involves the degradation of sugars to various end products like acid, alcohols, and gas
What sugars do the Triple Sugar Iron test contain
1.Glucose
2. Lactose
3. Sucrose
What is the pH indicator in the Triple Sugar Iron test?
phenol red
-turns yellow in the presence of acid (pH below 6.8)
What is something else the Triple Sugar Iron test detects?
-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
TSI: Appearance of red slant/red deep
no sugars fermented
TSI: Appearance of red slant/ yellow deep
-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
TSI: Appearance of yellow slant/ deep
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
TSI: Appearance of bubbles or cracks
-sometimes the media is pushed up from the bottom of the tube
-CO2 or H gas production
TSI: Appearance of a black precipitate
-can be found in the deep, but also extend to the slant
-hydrogen sulfide (H2S) production
What cultures did we used that need the TSI test to differentiate them?
- pseudomonas, Serratia, E.coli, and Proteus
-they all are gram negative and rod shaped
TSI test on E.coli
-ferment glucose, lactose, and sucrose
-produces CO2 and H gas
- no H2S production
* deep yellow and slant yellow
TSI test on Pseudomonas
- no sugar fermentation
-no gas production
-no H2S production - deep red and slant red
TSI test on Serratia
-ferment glucose only
- no gas production
-no H2S production
* deep yellow, red slant
TSI test on Proteus
- ferments sucrose only
- sometimes CO2 or H gas
-produces H2S production - deep yellow, red slant
citrate utilization
-determines the capability of an organism to utilize sodium citrate as the sole source of carbon
What are the chemicals used in citrate utilization test
- citrate as the sole carbon source
- Inorganic ammonium salts (NH4H2PO4) as the only source of nitrogen
- Bromothymol blue = pH indicator will turn blue if pH over 7.6 (original color is green)
How does the citrate utilization test work
-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
Exceptions to the citrate test
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
What bacteria was used in the citrate test
E.coli and Proteus
-both are gram negative and rod shaped
Citrate use test: E.Coli results
-does not use citrate as a carbon source
-green color
Citrate use test: Proteus results
use citrate as a carbon source
-blue color
catalase test
-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
