Microbiology Lab Quiz 2 (Biochemical tests, Cultural characteristics, Gram stain, spore stain)

broth

Liquid media used for propagation of large numbers of organisms and for various experiments and diagnostic tests

Slant

Solid media that gives the bacteria a greater surface area on which to grow in a tube.

- useful in maintaining bacterial cultures

Plate

Solid media particularly helpful in isolating a specific species of bacteria, which is not possible in a liquid medium

Synthetic medium

the chemical composition of the medium is known

Non-synthetic medium

Culture medium in which their exact composition is not known, most culture media

slaughterhouse waste/plant products and peptides, sugars, vitamins, minerals

How is non-synthetic medium typically made?

General purpose medium

Culture media that will support a wide range of organisms

Selective media

Culture medium used to select (isolate) specific groups of bacteria.

Incorporates chemical substances that inhibit the growth of one type of bacteria while permitting growth of another

How does selective media facilitate bacterial isolation?

Differential media

Culture media used to distinguish among morphologically and biochemically related groups of organisms.

- permit differentiation by incorporation of chemical compounds that produce

characteristic changes in the appearance of bacterial growth and/or the medium

surrounding the colonies

mannitol salt agar, eosin-methylene blue agar (levine)

Examples of media both selective and differential

Solid media (agar)

used to examine surface growth of organisms and to help in isolating organisms

General-purpose media examples

nutrient broth, trypticase soy broth, tryptone, peptone, and soy extract.

Purpose of heat-fixing a microbial smear

simultaneously kills and attaches the bacteria to the slide.

easier to see individual cell morphology, their arrangements, and details

Why is a thin microbial smear better than a thick smear?

to prevent contamination by eliminating unwanted microorganisms

Why is it important to disinfect the bench top?

to lower the risk of airborne particle contamination

Why is it better to hold a test tube horizontally when transferring cultures?

To sterilize it

Why is the mouth of the test tube flamed during aseptic transfer?

7 seconds in the incinerator or until it glows bright red

How is a metal loop sterilized?

to prevent contamination from airborne microorganisms

Why is it important to keep the lid on Petri plates and the cap on test tubes containing growth medium?

Simple stain

Used to determine if microbes are present in a sample, and to determine the size, shape and arrangement of the cell

Differential stain

Used when information not provided by the simple stain is needed, can detect the presence of flagella, endospores or a capsule

- some methods reveal information about the cell wall and presence of mycobacteria

Differential stain examples

gram stain, acid-fast stain, endospore stain

primary stain is crystal violet and the counterstain is safranin

What is the primary stain and counter-stain used in the Gram stain procedure?

Purple

Color of gram positive cell

Pink

Color of gram negative cell

to allow motile bacteria to easily move through the medium, enabling the observation of their swimming ability

Why does motility agar have a reduced concentration of agar?

indicated by diffuse (cloudy growth), especially at the top and bottom of the stab

What does a positive motility agar test look like?

isolate pure colonies

What is the purpose of a streak plate?

pure culture

contains only one kind of bacterium; ideally, it consists of the descendants of one bacterial cell.

turbidity

cloudiness, finely dispersed growth throughout the tube

pellicle

thick, pad-like growth across the top of the broth

sediment

cells have settled to the bottom of the tube

flocculent

flaky aggregates dispersed throughout the broth

to trap any gases that might be produced during the fermentation process

What is the function of the Durham tube in Phenol red glucose broth?

whether a microbe is capable of fermenting glucose and can also detect if the microbe produces gas during fermentation

What does the phenol red glucose broth test reveal about the test microbe?

Red; yellow

What is the color of the phenol red medium before inoculation and what color does it turn when acid is produced?

Methyl red

Name the pH indicator in the MR test

Iodine

What is added to starch agar after incubation?

if it can metabolize starch then it produces amylase

What does the starch agar test reveal about the test microbe?

Halo appears around the area of growth, outer edges of medium appear dark brown

What does a positive starch agar test look like?

tryptophan, an amino acid that can be metabolized by some microbes

What is being metabolized in tryptone broth?

Tryptophanase; catalyzes the conversion of tryptophan to pyruvic acid, ammonia, and indole.

Which enzyme is involved in the tryptone broth reaction?

pyruvic acid, ammonia, and indole

What are the end products in the tryptone broth test?

The presence of indole can be detected in the broth by adding Kovac's reagent.

How is the end product detected in the Tryptone Broth test?

If indole is present in the broth, Kovac's Reagent reacts with it to form a red product

What does a positive tryptone broth test look like?

If it is capable of fermenting glucose through the mixed acid fermentation pathway

What does the methyl red reveal about the test microbe in the VP test? (MRVP broth)

methyl red

What reagent is added to the MRVP broth after incubation?

red color in broth

What does a positive methyl red test look like?

Voges-Proskauer

What does VP stand for?

Reveals whether it can produce a neutral byproduct of glucose fermentation acetoin, a precursor of 2,3 butanediol.

What does the VP test reveal about the test microbe?

Acetoin

an intermediate compound of the fermentation process, can be easily

detected in the MRVP broth by adding Barett's reagents (VP A and VP B)

Barett's reagents (VP A and VP B)

What reagents are added in the VP test after incubation?

broth turns red color

What does a positive VP test look like?

if it can metabolize citrate and use it as a sole carbon source

What does the citrate test reveal about the test microbe?

Citrase (increases pH)

Which enzyme is involved in the citrate test reaction?

Green agar turns blue

What does a positive citrate test look like?

bromthymol blue

Which pH indicator is used in the citrate agar medium?