Micr Lab 6 Pt 2 end

Motility test

determine if an org contains flagella in order to move

Motility test directions

use needle-want straight as can get
-insert the needle all the way to the bottom of the tube and gently remove it
-remove as straight as possible as well

What do you do if you do move your needle?

make a note of which way (use your label as a reference) you moved it, as you can compare your results easier this way

What happens to the organisms as you move the needle through the media?

they become detached

Motile organisms:

Citrobacteer freundii
Enterobacter aerogenes
Escherichia coli
Proteus vulgaris
Salmonella typhimurium

Not Motile:


SIM tube

sulfur, indole, motility

When you read your results for the SIM test what do you want to record first?

read the sulfur and motility first


iron salts in media react with H2S to form a dark precipitate of iron sulfide, which is positive

Use the location of the sulfur to help determine what?

if the organism is motile
-if you cannot see through the media it is also motile

Formulas for Sulfur test

Cystenine (cystenine desulfurase) > NH(3) and Pyruvate and H(2)S
H(2)S> FeSO(4) > FeSH(2)SO(4) (black precipitate)

Positive Sulfur test: color and example

black precipitate
Proteus vulgaris

Negative: ex Sulfur Test

I guess no black is neg
Escherichia coli

Motility: what do you look for?

look for cloudiness throughout media and away from the stab line

Positive for motility

(note: some microbes have a light colony color so you need to remember how clear your uninoculated media looked)

Positive motility ex

Citrobacter freundii
Pseudomonas aeruginosa

Negative Motility ex

Staphylococcus aureus

Indole test detects what?

detects if organism produces tryptophanase


reduced tryptophan down to indole, pyruvic acid, and ammonia

What do you add to tube to test for typtophanase? Why do you add this?

Kovac's reagent
-indole is not used in any further chemical pathways so can use it to test

What happens when you add Kovac's reagent?

Kovac's reagent reacts with the indole to produce a bright red color on top of the media-positive

Positive result for Indole test and ex orgs

bright red color on top
Ex: Escherichia coli
Proteus vulgaris

Negative result for Indole test and ex orgs

no color change is negative
Ex: Enterobacter
Proteus mirabilis

How many drops of Kovac's reagent do you add? How long will it take for a color change?

add ten drops to deep tube
look for a color change within one minute

Formula for Indole test

Tryptophan (tryptophanase) > NH(3) and Pyruvate and Indole