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This is the first of Dr. Baumann's quizzes for Microbiology over labs 1-8

When do you flame the transfer loop?

Before and after any transfer of bacteria.

What is heat fix?

Quickly drying the bacteria samples on your slide so that they will not rinse off of the slide.

What does Crystal violet do?

This is the primary stain in a gram stain. This will color all cells blue.

What is a mordant or fixer?

In a gram stain, Gram's iodine is used. It reacts with the crystal violet and peptidoglycan to form a complex that is not easily dissolved.

What is a decolorizer in a gram stain procedure?

In a gram's stain, ethyl alcohol is used. This will remove the primary stain from all Gram NEGATIVE cells. At this point, Gram positive cells are blue and Gram negative cells are colorless.

Why is a counterstain used in a gram's stain?

Because after decolorizing with ethyl alcohol, the gram negative cells are colorless, this counterstain, safranin, will color the Gram negative cells and will not affect the Gram positive cells.

What color are gram negative cells?

Pink or red

What color are gram positive cells?

blue or violet

Why are gram positive cells blue?

The crystal violet will detect the protein peptidoglycan which is present in gram positive cell walls.

Bacillus cereus

gram positive, should be blue

Staphylococcus aureus

gram positive, should be blue

Escherichia coli

gram negative, should be red

Summary of steps in gram stain procedure

Primary stain (crystal violet)--> Mordant (Gram's iodine) --> Decolorizer (alcohol) --> Counter stain (Safranine)

What is the main purpose of doing a Grams Stain?

To find bacteria with peptidoglycan in their cell wall, gram positive.

What is the primary stain used in the Spore Stain?

Malachite green - this will stain the spores green

Why do you heat the slide during the staining process on a spore stain?

The properties of an endospore which help it to survive harsh conditions also make it difficult to stain. Heat enables the stain to penetrate the spore.

What is the counterstain used in the Spore

Safranin- this will stain the vegative cells red

Spore Stain picture should look like this:

The spores are green and the vegetative/dead portions of the cells are red. A complete cell should be red with a green spore in the middle.

carbol fuchsin

This is the primary stain in an Acid Fast stain. The color is a pretty magenta. This stain will stain all cells magenta. After the decolorization process, the acid fast cells will remain magenta or red.

methylene blue

This is counter stain in an acid fast stain. The color is blue. This stain will remain in the NON acid fast cells.

What cells are Acid fast in the Acid fast stain lab?

Mycobacterium smegmatis remains red, this is acid fast. M. tuberculosis is also an acid fast cell.

What cells are NON acid fast in the acid fast stain lab?

Staphylococcus aureus is blue, this is NON acid fast

What component of a cell will stain in an Acid Fast stain?

Mycolic acid.

Desoxycholate agar is selective for...

Escheriechia coli grows on this agar as pink. The color is pink because it contains lactose. E. coli is a lactose fermenting colony, so it will produce pink colonies.

Mannitol salt agar is selective for ....

Staphylococcus aureus is able to ferment mannitol. The yellow zones indicate the presence of these colonies.

Sodium Azide agar is selective for.....

Streptococcus faecium and Staphylococcus Aureus - these 2 bacteria are resistent to the killing effects of Sodium Azide

Blood agar contains many nutrients for fastidious pathogens

This is a partial hemolysis, the green zones around the colonies

Blood agar sample of a beta hemolysis, complete

Many pathogens are beta hemolytic. The clear agar is the proof that this is a beta sample.

Blood agar sample of no hemolysis, gamma sample

There is no green on this plate or see through agar, so this is NO hemolysis.

Differential media

Contains substances that exhibit a definite visible appearance when affected by one type of bacteria and a different appearance when affected by a second type of bacteria.

Selective media

Contains chemicals which inhibit the growth of certain types of bacteria without inhibiting others. A medium may be both selective and differential.

Enriched media

Contains extra nutrients needed by certain types of bacteria so that their growth is encouraged.

What is the plate streak method used for?

It is one of the most simplest methods of isolating pure cultures.

What color on the streak plate is the Staphylococcus aureus?


What color on the streak plate is the Serratia marcescens?


What is the obligate anaerobe used in lab 7?

Clostridium sporogenes. This pathogen should have cracked the agar in the test tube due to gas in the anaerobic agar. Ours didn't, Dr. Baumann said that the sample probably died.

Staphylococcus aureus

NON motile

Escherichia coli


Proteus vulgaris


Spell "Staphylococcus aureus"

Staphylococcus aureus

Spell "Proteus vulgaris"

Proteus vulgaris

Spell "Escherichia coli"

Escherichia coli

Spell "Clostridium sporogenes"

Clostridium sporogenes

Spell "Streptococcus faecium"

Streptococcus faecium

Spell "Serratia marcescens"

Serratia marcescens

Spell "Mycobacterium smegmatis"

Mycobacterium smegmatis

Spell "Bacillus cereus"

Bacillus cereus

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