Exercise 8: Cultural and Physiological Characteristics of Bacteria Part I

What are the agar plate tests for exoenzymes?

-lipase

-milk agar

-starch agar

Exoenzymes tests are all on what kind of media?

agar plates

What are the tube media tests for other metabolic processes?

-litmus milk

-sugar fermentation broth

-Kingler's Iron Agar (KIA)

Tube media test are all what kind of media?

liquid

Litmus milk contains:

-lactose

-casein and other peptones

-Litmus pH indicator

Litmus milk tests for what?

-fermentation of lactose

-metabolism of proteins

-degradation of casein

-Litmus reduction

Casein is:

milk protein

Litmus milk will only produce one reaction, T or F?

false; can produce multiple reactions

What are the possible reactions one can find with litmus milk? (5)

-acid production

-alkaline production

-curd

-reduction (redox)

-proteolysis

Fermentation of lactose will produce what? Reduce or increase pH?

will produce acid; will reduce the pH

What color will the litmus mill turn at an acidic pH?

pink

A weak fermentation in litmus milk will appear how?

Purplish color; bottom of tube will look milky purple, top of tube will have a cloudy/purply/lavender color (slight pink color)

A strong fermentation in litmus milk will appear how?

bottom of tube will be cloudy milk color; top of tube will be pink in color

The control of litmus milk is what color?

purple

In peptone deamination, what is being released in the litmus milk?

ammonia

In peptone deamination, the pH lowers/raises?

raises

What color does the litmus milk turn with peptone deamination?

blue

Peptone deamination is dependent on ____, so the color change may be limited the top/bottom of tube?

oxygen; top

Litmus milk only function as a pH indicator in what redox state?

oxidized

Litmus milk will lose its color when it is:

reduced

If the litmus milk turns white, what has happened? It is typically seen at the bottom of the tube why? Why will there still be a band of color on top?

it has been reduced; little to no oxygen--->oxygen cannot penetrate and re-oxidize the litmus indicator; color still persists on top b/c oxygen is present and can re-oxidize the litmus I indicator

Some bacteria produce what enzyme?

caseinase

If casein is degraded, what color will the milk turn?

will be clear (not opaque)

What leads to curding?

If enough acid is produced from the fermentation, denaturing will occur aka curding

Curding ALWAYS occurs with acid production, T or F?

false; does not always occur

Phenol Red (PR) Sugar fermentation contains how many sugars?

one

What sugar does the PR test use?

either glucose, lactose, or mannitol

What are the indicators for the PR sugar test?

phenol red and a Durham tube

phenol red tests for:

pH

Durham tube tests for:

gas formation

If an organism ferments in PR, what color does the phenol red turn in a PR test?

yellow

If an organism produces gas, what happens to the Durham tube?

a bubble collects inside it

If an organism does not ferment, what color does the phenol red turn in a PR test?

turns a shade of hot pink called cerise

If an organism does not ferment in a PR test, what is happening? What is it releasing?

peptone deamination; ammonia

What does Kligler's Iron Agar (KIA) test for?

-lactose fermentation

-glucose fermentation

-sulfur reduction

What are the carbohydrate sources for KIA?

1.0% lactose and 0.1% glucose

What are other ingredients in KIA and what are they a source for?

1.0% peptone and it is a source of ammonia and sulfur via cysteine

What are the indicators for a KIA test?

phenol red (pH indicator) and iron

in KIA, the iron comes from? Combines with? Forms what?

comes from ferric ammonium citrate; combines with H2S; forms a black precipitate

The iron in KIA detects? Will indicate?

hydrogen sulfide; indicates sulfur reduction

KIA uses what kind of media?

slant media (solid)

in KIA, if both glucose and lactose are fermented, the entire tube will turn what color?

yellow

Which sugar gets fermented first in KIA, glucose or lactose?

glucose

If gas is produced during fermentation in KIA, how will one be able to tell?

lifting or cracking of the media in tube

If glucose only is fermented in KIA, how will the tube look like? Which color indicates glucose fermentation?

Red on top portion of slant all the way to the bottom of slant portion, yellow on butt portion of slant; yellow indicate glucose fermentation

If a red color is seen on KIA but it does not go to the bottom of the slant portion, this means it only ferments glucose, T or F?

false; also ferments lactose, just weaker at it

Which bacteria is known to produce weak acids in a KIA fermenting test? Why?

Enterobacter aerogenes; b/c it used the 2,3-butanediol pathway for lactose fermentation which produces less acid

In KIA, if it ferments lactose, it can ferment glucose, T or F?

true

In KIA, sulfur reduction will be what color and where? Why

black and bottom/butt of tube; b/c of precipitate

Black precipitate indicates what?

that fermentation and acid production have occurred

In KIA, if it is positive for sulfur reduction, it is positive for glucose, T or F?

true

Lipase plate is an example of what kind of media?

differential

The lipase plate tests for what enzyme?

lipase

What is the indicator in a lipase plate?

spirit blue

How can one tell if hydrolysis of lipids as occurred?

hydrolysis of lipids produce a dark blue zone around the growth with no oily surface

For lipase plate, a positive result has:

a blue color

For lipase plate, and negative result has:

no color

Milk agar plate is an example of what kind of media?

differential

Milk agar plate tests for what enzyme?

caseinase

Caseinase hydrolyses what protein?

casein

Casein gives milk its ___ color

white

When casein is broken down, it will:

lose its color; clearing

in milk agar plate, a positive result will be:

clear around the colony

in milk agar plate, a negative result will have:;

no clearing around the colony

Starch agar is an example of what kind of media?

differential

Starch agar tests for what enzyme?

amylase

What do you add to the colony in a starch agar plate as the indicator?

iodine

What color will form around the border of the colony if it is positive for amylase?

purple