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Enzymatic activity of bacteria can be observed by using what?

Differential media


What is the goal of differential media

It will aid in the identification of unknown gram negative rods in the Enterobacteriaceae family


Enterobacteriaceae family include

Normal gastrointestinal microbiota, opportunists, and pathogens.


Infections cause by enterics include

Sepsis and meningitis


Types of standard differential tube media:

-Simmon's Citrate Agar (SCA)
-Urea agar
-Sulfide-Indole-Mobility (SIM) medium
-Triple Sugar Iron ( TSI)


SIM media

Is a combined media that tests for motility, sulfur reduction to hydrogen sulfide H2S


H2S production in SIM:
What does the SIM media contains? What color is it turn when combined to H2S?

SIM contains ferrous sulfate ( iron salt)
That turn black when combine to H2S gas


Motility in SIM:
When are bacteria motile? Non motile?

If the bacteria swim away from the line of inoculation (stab), they are motile.
If the bacteria grow only along the stab line, they are non motile.


What is tryptophanase?

It is an enzyme produce by some bacteria.


What does tryptophanase do?

Are able to hydrolyze the amino acid tryptophan producing Indole and pyruvate.


Simmon's Citrate is used to

Differential gram negative bacteria on the basis of citric acid utilization.


What does agar medium contains?

Sodium citrate as the only available carbon source.


What indicator the medium agar contain

Bromthymol blue, which is green at pH 6.9 and blue at pH 7.6


Organisms which have the enzyme citrase, are able of what?

They are able to to utilize the sodium citrate and nitrogen sources and produce ammonia.
Convert the agar to alkaline pH and a blue color


Triple Sugar Agar contains how many carbohydrates?
The medium contain what?
What indicator? Color?

-Three carbohydrates : glucose, sucrose and lactose.
-Peptones as a carbon and nitrogen source
-phenol red ( is yellow in acidic pH and pink red I. Alkaline pH).



It is when peptones ( amino acid) are used for food, ammonia is produced


Urea hydrolysis:
Urea agar contains?
When urease positive bacteria are inoculated, medium do what?

-It is an enzyme which hydrolyze a certain amino acids and urea to ammonia and carbon dioxide.
- urea, peptones, glucose and phenol red.
-medium becomes alkaline turning the phenol red indicator bright pink.


&beta galactosidase enzyme causes the release of what?& glucosidase enzyme? Tryptophan deaminase enzyme?

-release of a dye turning the colonies pink.
-turn colonies to blue.
-turn the media to beige brown


What is a smear? Its Role?
Why do you the heating treatment?

-It is the application of the bacteria to a slide for purpose of staining.
- so the cells are not piled on top of each other.
- to kill the bacteria and stick them to the plate.


Time for gram stain:
-Crystal violet, let stand for?
-Hold the slide at what angle to wash w/c water?
- wash w/c water for?
- Gram 's iodine?
- Gram's alcohol for?
-Safranin for?

- 30 sec
- 45 degree
- 2 sec
- 1 min
- 5 to 10 sec
- 45sec