MICRO LAB- Biochem of Enterics

iMViC Series

Used to confirm species of gram negative “coliform” bacteria

MacConkey agar plate

Used to check for “coliform” bacteria, which are gram negative organisms that can ferment lactose. Some bacteria occur naturally in the environment, but many come from the feces of warm-blooded animals and humans, which may be pathogenic

• water potability tests verify the presence of harmless or pathogenic coliform bacteria using the IMViC series

selective and differential medium

• Selective agents: Bile salts and crystal violet select for gram negative and against gram positive bacteria

• Differential agents: Neutral red pH indicator turns pink under acidic conditions

Lactose ————————> Acid end products

MacConkey Agar Plate

• medium: macconkey agar

• substrate: lactose

• enzyme: N/A

• other reagents: Selective agents (bile salts and crystal violet), Differential agent (neutral red pH indicator)

Indole

• test for the enzyme tryptophanase

tryptophan + H2O ——--(tryptophanase)—→ indole + pyruvate + ammonia

Indole

• Medium: Tryptone broth (TSB)

• Substrate: Tryptophan

• Enzyme: Tryptophanase

• Other reagents: Kovac’s indole reagent

Citrate

• tests for aerobic use of citrate

Citrate————→ alkaline end products

Citrate

• medium: simmons citrate agar

• substrate: citrate

• Enzyme: N/A

• Other reagents: Brothymol Blue (pH indicator)

Methyl red

• tests for mized acid fermentation

Glucose ————→ mixed acids (pH < 4.5)

Methyl red

• medium: MRVP Broth

• Substrate: Glucose

• Enzyme: N/A

• Other reagents: Methyl Red (turns red at pH < 4.5)

Vogues Proskaur

• tests for the butelyene glycol pathway

Glucose ————> AMC ———> Butylene glycol (4.5 > pH > 7)

Vogues Proskaur

• medium: MRVP Broth

• Substrate: Glucose

• Enzyme: N/A

• Other reagents: a-Napthol, Potassium hydroxide (KOH)

The IMViC series consists of how many different tests?

4

What attributes do the Methyl Red and the Voges-Proskaur tests have in common? (select all that apply)

• same substrate

• same media

How many different organisms will you use to inoculate a single plate of MacConkey agar

3

MacConkey agar has a pH indicator named                                 , and if fermentation takes place, the medium will turn                             .

Neutral red; pink

If an organisms grows well on MacConkey agar, most likely it

is gram negative

Citrate usage produces                                         end products. A positive test for citrate means the pH indicator, bromthymol blue, will display a                              color.

alkaline; blue

You will inoculate two tubes of MRVP broth with the exact same organism on the first day of this lab. One tube of MRVP broth will be used for the methyl red test. The other tube of MRVP broth will be used for the Voges-Proskaur test.

Even though you will not perform every test on every organism, yourself. You still must know all of the results to complete the lab report.

The MacConkey agar tests for lactose fermentation. If an organism does not grow on it, you assume the organism is negative for lactose fermentation.

False; Good job. This is false. If the organism does not grow, we cannot know whether it would have fermented the lactose in the medium.