Microbiology Lab Exam 2

Simple staining gives the viewer clues as to the cell wall structure of a bacterial cell. True or False

False Only basic dyes will actually stain negatively charged bacterial cells. Acidic stains like eosin stain the background of a slide, not the cells themselves. These types of stains are useful in negative and capsule staining.

The Gram stain technique is a ______ staining technique. structural negative differential simple

differential

For the negative stain procedure, one can use nigrosin. India ink. malachite green. either India ink or nigrosin. All of the choices are correct.

either India ink or nigrosin

The thinner peptidoglycan layer of gram-positive bacteria allows the crystal-violet-iodine complex to leave the cell. True or False

false

Acid-fast cell walls have a high lipid content, including a waxy material called ______. mycolic acid coagulase phospholipid carbolfuchsin

mycolic acid

Please choose the answer that best completes the blanks of this sentence in the correct order. After acid-fast staining, Mycobacterium tuberculosis would be _______ in color, whereas Proteus vulgaris would be ________ in color. purple; pink blue; red red; green red; blue

red; blue

What medically-important organism can be detected using the acid-fast stain? Mycobacterium tuberculosis Escherichia coli Staphylococcus aureus Clostridium botulinum

Mycobacterium tuberculosis

Which two bacterial genera will usually stain red during the acid-fast staining procedure? Nocardia Mycobacterium Staphylococcus Corynebacterium

Nocardia mycobacterium

What makes Mycobacterium particularly resistant to staining? The presence of endospores The presence of mycolic acid in their cell walls Their lack of a cell wall to trap the dye molecules Their susceptibility to lysis when heat is applied

The presence of mycolic acid in their cell walls

Why does culture age affect the results of a spore stain? Younger cultures are more active metabolically. Younger cultures are most likely to produce spores due to adequate nutrition. Older cultures are most likely to produce spores due to depleted nutrition. All smears should be made from young cultures to ensure correct morphology.

Older cultures are most likely to produce spores due to depleted nutrition.

How many different dyes are used when simple staining a bacterial smear? Three One Correct Two

One

Palisades arrangement

Parallel arrangement of bacilli

If a Gram-stained slide of the CSF sample was void of cells, what would be the likely causative agent? Fungal agent Neisseria meningitidis Streptococcus pneumoniae Viral agent

Viral agent

Streptococci

Spherical bacteria in chains

In this woman's case, the presence of red diplococci indicated that the causative agent was an RNA virus. a fungus. a gram-positive bacterium. a gram-negative bacterium.

a gram-negative bacterium.

The differential step in the acid-fast stain method is the application of ______. acid-alcohol carbolfuchsin water heat

acid-alcohol

Rod-shaped bacteria are never gram-positive or gram-negative. are all gram-negative. can be either gram-positive or gram-negative. are all gram-positive.

can be either gram-positive or gram-negative.

What is the role of water in this staining method? Secondary stain Decolorizer Mordant

decolorizer

The stain used in this demonstration of the simple stain method is ______. methylene blue Correct crystal violet nigrosin safranin

methylene blue

Select all of the following that represent examples of simple stains. Check All That Apply Nigrosin Methylene blue Crystal violet India Ink Basic fuchsin

methylene blue, basic fuchsin crystal violet.

A _______ stain is one that colors the background surrounding the cell, leaving the cell itself unstained. negative differential positive complex

negative

Please choose the answer that best fills in the blanks of this sentence in the correct order. Gram-________ cells stain purple whereas gram-_______ cells stain pink or red when using the Gram stain technique. negative; positive positive; negative

positive; negative

A slide prepared with a simple staining technique is useful in determining ________. (Check all that apply.) shape of individual cells arrangement of cells presence of granules within cells the species of a particular bacterium the biochemical identity of a cell

shape of individual cells arrangement of cells presence of granules within cells

The term used to describe a cluster of circular bacteria is _________. streptobacilli staphylococci vibrio streptococci

staphylococci

Why is endospore staining important? It separates bacteria from protozoans under the microscope. It helps in identifying the few medically important genera that produces endospores. It demonstrates the reproductive capacity of a genus. It helps in identifying the antibiotic susceptibility of a species

It helps in identifying the few medically important genera that produces endospores.

What is the primary stain used in the Schaeffer-Fulton staining method? Malachite green Carbolfuchsin Safranin Methylene blue

Malachite green

If the Gram's iodine step was skipped in this technique, what would likely be seen under the microscope? Most cells appear purple. Most cells would appear red/pink. All cells appear colorless. Most cells would appear blue.

Most cells would appear red/pink.

Endospore staining is a good example of a _______ stain technique. differential negative fluorescent simple

differential

The differential stage of the Gram stain is the application of _____. iodine safranin ethanol crystal violet

ethanol

Please choose the answer that best completes the blanks of this sentence in correct order. Basic or cationic dyes have a ______ charge which are attracted to negatively-charged bacteria, whereas acidic or anionic dyes have a ______ charge and do not stain bacteria. negative; positive positive; negative negative; neutral neutral; positive

positive; negative

When ethanol is applied correctly, gram-positive cells appear ____ and gram-negative cells appear _____. purple; pink/red pink/red; purple purple; colorless colorless; purple

purple; colorless

After the application of acid-alcohol, what color would Mycobacterium leprae cells be? Blue Red Clear

red

Which genera represent endospore-forming bacteria? Clostridium and Staphylococcus Clostridium and Bacillus Bacillus and Streptococcus Bacillus and Neisseria

Clostridium and Bacillus

If you were to forget the safranin, what color would gram-negative cells be after the stain is done? Colorless Brown Red/pink Purple

Colorless

All bacteria can be classified as either gram-positive or gram-negative. True or False

False

Bacteria are larger than human cells. True or False

False

Bacteria are only visible with an electron microscope. True or false

False

For every bacterial cell that undergoes sporulation, there are two resulting bacterial cells. True or False

False

The presence of flagella can be determined by a Gram stain. True or False

False

A simple stain of a patient specimen would always be helpful in determining the right antibiotic to use in therapy. True or False

False A simple stain can only give some clues about the identity of a bacterial species. In most cases, this technique would not be enough to determine the causative agent and therefore, choose the best antibiotic. Typically, Gram staining is more helpful in this area.

Alcohol is used to decolorize the background of the slide to allow for the visualization of cells. True or False

False Water is used to rinse off excess stain in this simple staining process.

If you decolorize a slide for too long, what outcome is likely? Gram-positive cells will appear gram-negative. All cells will appear purple due to the mordant. Gram-negative cells will appear gram-positive. All cells will likely be colorless.

Gram-positive cells will appear gram-negative.

If you were to forget to add crystal violet, how would that change the outcome of the stain? Gram-negative cells would be purple instead of red/pink. All cells would be purple in color. All cells would be colorless. Gram-positive cells would be red/pink instead of purple.

Gram-positive cells would be red/pink instead of purple.

What is used as a mordant in the acid-fast stain method? Acid-alcohol Iodine Water Heat

Heat

Why is negative staining useful for accurately determining cell size? Multiple Choice The stains used dehydrate the cells, allowing for accurate measurement. Heat fixation is performed, fixing the cells to the slide true to size. The cells are stained with a high contrast dye, allowing the borders to appear clearly. Heat fixation is not performed so cells do not shrink.

Heat fixation is not performed so cells do not shrink.

What is the purpose of heat fixation? To eliminate contaminating organisms on the slide To adhere the cells to the slide for the staining process To disperse the cells evenly for easier viewing of single cells

To adhere the cells to the slide for the staining process

Which is NOT a purpose of using the Gram stain in the diagnostic process? To determine that the infection is bacterial instead of viral To confirm the identity of the pathogenic agent To give guidance for drug treatment To determine what type of bacteria may be causing the infection

To confirm the identity of the pathogenic agent

The final result of a Schaeffer-Fulton stained slide is green spores and purple sporangium. pink spores and green sporangium. green spores and pink sporangium. clear spores and pink sporangium.

green spores and pink sporangium.

If you forgot to apply heat during the primary staining process with carbolfuchsin, what might occur? Acid-fast cells may not stain correctly. All cells will remain colorless after the acid-fast staining method. Non-acid-fast cells may appear red after staining.

Acid-fast cells may not stain correctly.

Which of the following would NOT work to stain bacterial cells? Crystal violet Acidic eosin Correct Methylene blue Basic fuchsin

Acidic eosin

What reagent is used to form insoluble complexes, therefore trapping dye inside of cells? Alcohol Decolorizer Mordant Counterstain

Mordant

If steam is not applied during the malachite green step, what is a likely result at the end of the staining procedure? Both spores and sporangium may be pink. Both spores and sporangium may be clear. Only sporangium will be green. Both spores and sporangium may be green.

Both spores and sporangium may be pink.

Acid-fast cells

Cells which contain a thick layer of mycolic acid or cord factor

Gram-positive cells

Cells which contain a thick layer of peptidoglycan and teichoic acids

Gram-negative cells

Cells which contain both an inner and outer membrane as well as a thin layer of peptidoglyan

What color would Staphylococcus aureus be on the slide after acid-fast staining? Clear Blue Green Red

Blue

What is an endospore? A vegetative structure with a lowered metabolic rate A reproductive structure used by bacteria for population growth A dormant structure formed by bacteria in response to nutrient depletion A dormant structure used by bacteria in response to higher temperatures

A dormant structure formed by bacteria in response to nutrient depletion

Why is it important to use fresh cultures for Gram staining? multiple choice Aging changes the metabolism of the cell. Aging affects the reaction with the mordant. Aging changes the peptidoglycan layer in cells. This isn't important -- older cells stain as well as younger cells.

Aging changes the peptidoglycan layer in cells.

The most critical step in the Gram stain technique involves what reagent? Safranin Crystal violet Alcohol Iodine

Alcohol

After Gram's iodine is added, what color do the cells appear under a light microscope? Some cells may be purple and some may be pink/red. All cells appear purple. All cells appear colorless. All cells appear pink/red.

All cells appear purple.

If you were to observe the cells under the microscope after the addition of the Gram's iodine, what would their color be? All cells would be brown. All cells would be colorless. All cells would be purple. All cells would be red/pink.

All cells would be purple.

If you were observing long rod-shaped cells on a simple stained slide, what genus might you be looking at? Neisseria Staphylococcus Streptococcus Bacillus

Bacillus

What is the primary stain used in the acid-fast stain method? Malachite green Carbolfuchsin Methylene blue Safranin

Carbolfuchsin

Order the reagents used in the acid-fast staining procedure. Methylene blue Acid-alcohol Carbolfuchsin

Carbolfuchsin Acid-alcohol Methylene blue

What is the correct order of reagents in the acid-fast stain method? Safranin, Acid-Alcohol, Methylene Blue Carbolfuchsin, Ethanol, Methylene Blue Carbolfuchsin, Acid-Alcohol, Methylene Blue Methylene Blue, Acid-Alcohol, Carbolfuchsin

Carbolfuchsin, Acid-Alcohol, Methylene Blue

What microbial characteristic is differentiated by the Gram stain technique? Cell wall composition Presence of a capsule DNA fingerprint Ability to ferment sugar

Cell wall composition

How do gram-positive and gram-negative bacteria differ in their cellular structure? Number of ribosomes Composition of cell membrane Cell wall structure Presence of a nucleus

Cell wall structure

Based on the scientific name of the species Streptococcus pyogenes, what would you expect to see under the microscope after a simple stain procedure? Chains of rod-shaped cells Clusters of spherical cells Chains of spherical cells No particular arrangement of spherical cells

Chains of spherical cells

What is the correct order of staining materials used in the Gram stain technique? Crystal violet, Gram's Iodine, 95% Ethanol, Safranin Safranin, Gram's Iodine, 95% Ethanol, Crystal violet Crystal violet, Gram's Iodine, 95% Ethanol, Carbolfuchsin Methylene blue, 95% Alcohol, Gram's Iodine, Safranin

Crystal violet, Gram's Iodine, 95% Ethanol, Safranin

Choose the correct order of reagents as applied in the Gram stain technique. Crystal violet, iodine, water, safranin Crystal violet, iodine, alcohol, safranin Crystal violet, alcohol, iodine, safranin Safranin, iodine, alcohol, crystal violet

Crystal violet, iodine, alcohol, safranin

What reagents used in the Gram stain technique are colored dyes? Safranin; ethyl alcohol Crystal violet; basic fuchsin Crystal violet; iodine Crystal violet; safranin

Crystal violet; safranin

What type of microscopy produces an image of unstained cells that is similar to one achieved by negative staining? Multiple Choice Brightfield Darkfield Phase-contrast Fluorescence

Darkfield

What general type of stain is used to separate types of bacteria based on their cellular structures? Simple Differential Negative Acidic

Differential

Why must fresh cells be used when performing a Gram stain? All of these are reasons why fresh cells must be used for Gram staining. Fresh cells do not smell as badly as older cells. Old cells may not Gram stain properly. As cells age, they won't stick to the slide.

Old cells may not Gram stain properly.

What is most likely indicated by the cloudiness of the cerebrospinal fluid obtained from the second spinal puncture? Failure of the kidneys to clear the body of wastes Presence of excessive wastes in fluid Presence of microbes in normally sterile fluid Liver insufficiency

Presence of microbes in normally sterile fluid

If you mistakenly use water instead of alcohol in the decolorization step, predict what color all cells would be after the stain is done. Colorless Purple Brown Red/pink

Purple

A culture of Staphylococcus aureus, a gram-positive coccus, is about 48 hours old. What color would these cells likely appear under the microscope after Gram staining? Red/pink Purple Colorless

Red/pink

What will you be able to observe on the slide after this procedure? Presence/absence of nuclei in blue cells Cell wall structure of blue or red cells Shape and arrangement of purple or pink cells Shape and arrangement of blue cells

Shape and arrangement of blue cells

If a Gram stain of the CSF sample yielded gram-positive cocci, what would be the likely causative agent? Haemophilus influenzae Neisseria meningitidis Measles virus Streptococcus pneumoniae

Streptococcus pneumoniae

Spirochaete

Spiral bacterium

What is safranin used for in this staining method? Used as a mordant Staining the vegetative cells Staining the endospores

Staining the vegetative cells

What is used as a mordant in this endospore staining method? Malachite green Water Safranin Steam

Steam

Which of these symptoms pointed the doctors to a possible central nervous system infection? Stiff neck Sore throat Fever Aching joints

Stiff neck

What is incorrect/missing in the steps below for the proper technique for making a smear? • Label a slide.• Place a small drop of water on the slide.• Gently pick up an isolated colony from a Petri dish.• Immerse and suspend the colony.• Sterilize the inoculating loop.• Let slide dry for five minutes. The inoculating loop should be sterilized before picking up a colony from the dish. The slide should be heat fixed before it dries for five minutes. Water should be added to the suspended colony. An inoculating needle should be used in the immersion process.

The inoculating loop should be sterilized before picking up a colony from the dish.

You make a smear of E. coli and then simple stain the slide with methylene blue. If you failed to use correct aseptic technique by not sterilizing the loop before picking up the bacterial sample for the smear, what results may be seen under the microscope? No cells may be visible on the slide. Both blue and purple cells may be seen on the slide. There may be cells of different shapes, sizes, and arrangements.

There may be cells of different shapes, sizes, and arrangements.

Please choose the answer that best completes the blanks of this sentence in the correct order. _______ is used to stain the endospore, and _______ is the stain used to stain the vegetative cell in the Schaeffer-Fulton method of spore staining. Safranin; malachite green Methylene blue; safranin Malachite green; carbolfuchsin Malachite green; safranin

Malachite green; safranin