biochemical tests

What is the purpose of agar?

NOT
To solidify media, serve as a carbon substrate for bacteria, and to provide an energy source for bacteria.

try To solidify media

Below are two pictures of mannitol salts agar. Click on the picture of mannitol salts agar where the mannitol has been fermented.

green one (right side)

Fermentation of sugars produces ____.

acidity

What is the pH indicator dye in Mannitol Salt Agar?

phenol red

What is the substrate in Mannitol Salt Agar?

mannitol

Catalase helps protect bacterial cells from

Correct answer:

Reactive Oxygen Species (ROS).

ss

Water

is produced when catalase breaks down a reactive oxygen species.

ss

What is the substrate that catalase enzyme acts on?

hydrogen peroxide

An ___ is most likely to have catalase.

Correct answer:

aerobic bacteria

sss

Below is a photo of two microbial cultures treated with hydrogen peroxide. Click on the culture that is catalase positive.

the bubbled one

what kind of enzyme breaks down in the presence of oxygen?

oxygen labile enzyme

Streptococcus pyogenes is ___ hemolytic bacterium.

a beta

Which kind of bacteria are capable of completely destroying red blood cells?

beta hemolytic bacteria

If an organism produces

Correct answer:

beta

hemolytic toxins, the zone of clearing will be

Correct answer:

transparent

so you can read through it.

sss

To test for hemolytic activity, the agar is amended with

Correct answer:

sheeps blood with intact red blood cells.

sss

Click on the culture that exhibits alpha hemolytic activity.

bottom left

Click on the culture that exhibits beta hemolytic activity.

top left

If an organism is DNase positive, a culture grown on DNase Test agar will have

zone of clearing

The indicator dye in DNase plates forms

a green dye when it binds to polymerized DNA.

Click on the bacterial culture that is DNase positive.

left side

What is the indicator dye in DNase Agar?

Correct answer:

methyl green

ss

Click on the culture that is positive for starch hydrolysis.

bottom

A culture that is negative for starch hydrolysis will

not have a halo around them because there has been no starch hydrolysis. 

What chemical is added to the starch agar to produce a brown pigment in the presence of starch?

iodine

What are two kinds of starch?

amylose

Correct answer:

amylopectin

The substrate in Citrate Test Agar is ____

citrate

The pH indicator in citrate agar is _

bromothymol blue

Below is a photo of two different culture of bacteria grown on Citrate Test Agar. Click on the culture that has a positive test result. 

blue one

Which organism is more commonly pathogenic?

s. aureus

Which organism is gelatinase negative?

Staphylococcus epidermidis

, Not Selected

Staphylococcus aureus

s. epidermis

Click on the culture of bacteria that is gelatinase negative.

tube w liquid thats not bent

What is the indicator dye in the urease test agar?

phenol red

What group of bacteria is commonly capable of degrading urea?

proteus

Urea breaks down into carbon dioxide and ammonia. Which one will raise the pH of the Urease Test Agar?

ammonia

Below is a photo of urease test agar after a 16 hour incubation at 37 degrees C. Click on the tube that was inoculated with a slow urease positive organism.

pink slant yellow butt

Decarboxylation of lysine will cause the pH to ___.

increase

The sugar in lysine iron agar is ___.

glucose

lysine deamination is an 

aerobic process only

Decarboxylating lysine will produce an amine called ____

cadaverine

A LIA tube with a red slant and yellow butt would be scored

Correct answer:

R/A

and is indicates the organism is

Correct answer:

lysine deaminase positive

ss

Below is a photo of 3 different organisms cultured in Lysine Iron Agar. Click on the tube you would score as K/A

purple slant yellow butt

Below is a photo of 3 different organisms cultured in Lysine Iron Agar. Click on the tube that is positive for glucose fermentation but negative for both lysine deamination and decarboxylation.

purple slant yellow butt

What are the three sugars in triple sugar iron agar?

sucrose

Correct answer:

lactose

Correct answer:

glucose

Triple sugar iron agar contains

Correct answer:

0.1%

glucose,

Correct answer:

1%

lactose, and

Correct answer:

1%

sucrose.

ss

In Triple Sugar Iron Agar, if proteins are digested, then 

pH up, agar red

In Triple Sugar Iron Agar, if sugars are fermented then

pH down, agar yellow

if a triple sugar iron agar tube presented with a purple slant and a yellow butt, then the tube would be scored as 

K/A

If a triple sugar iron agar tube presented with a purple slant and a yellow butt, then the tube would be interpreted as

a species of bacteria only capable of fermenting glucose.

Below are four cultures grown in triple sugar iron agar. Click on the culture that would be scored A/A + H₂S

brown slant black butt

If a triple sugar iron agar tube presented with a yellow slant and a black precipitate, then the tube would be interpreted as

NOT a species of bacteria capable of fermenting glucose and reducing thiosulfate into hydrogen sulfide.

try A species of bacteria capable of fermenting sucrose, lactose, or both, in addition to fermenting glucose and capable of reducing thiosulfate into hydrogen sulfide.

Bromothymol blue turns from green to prussian blue at a pH greater than or equal to ___.

7.6

Below is a photo of two different culture of bacteria grown on Citrate Test Agar. Click on the culture that has a negative test result. 

green

Gelatin is a ___.

protein

At 37 degrees C, gelatin would be a

Correct answer:

liquid

; therefore, it is necessary to put cultures in

Correct answer:

an ice bath

to get an accurate test result.

ss

Click on the culture of bacteria that is gelatinase positive.

the slanted liquid in a slanted tube

Urease test media is a ____ medium.

defined

Below is a photo of urease test agar after a 16 hour incubation at 37 degrees C. Click on the tube that was inoculated with a rapid urease positive organism.

full pink

Deamination of lysine will cause the slant to turn red because 

the products of lysine deamination react with ferric ammonium citrate to produce a red color.

A LIA tube with a purple slant and purple butt would be scored

Correct answer:

K/K

and is indicates the organism is

Correct answer:

lysine decarboxylation positive

ss

If a triple sugar iron agar tube presented with a red slant and a black precipitate, then the tube would be scored as 

K/A + H₂S

Below are four cultures grown in triple sugar iron agar. Click on the culture that would be scored K/A + H₂S

red slant black butt

If a triple sugar iron agar tube presented with a red slant and a black precipitate, then the tube would be interpreted as

a species of bacteria capable of fermenting glucose and reducing thiosulfate into hydrogen sulfide.