BIOL 2730 - Microbiology Lab Master Flashcards

Master Q&A flashcard set covering BIOL 2730 Microbiology Lab material across exercises 5 through 57.

What three broad groups are examined in Exercise 5?

Protozoa, algae, and cyanobacteria.

Which groups examined in Exercise 5 are eukaryotic?

Protozoa and algae.

Which group examined in Exercise 5 is prokaryotic?

Cyanobacteria.

What is the main purpose of Exercise 5?

To observe, identify, and categorize organisms in pond water.

Why are the relevant figures important in Exercise 5?

This is a visual-identification exercise; use the figures to practice recognition.

What identification is required in the Exercise 5 lab report?

Genus and group identification.

How is microbial growth recognized in liquid medium?

The medium becomes turbid/cloudy.

What does a visible bacterial colony generally contain?

Hundreds of cells.

What does solid culture provide that liquid culture does not?

Visible colonies that can be examined for characteristics and separation.

What is the relationship between a cell and a colony?

A colony is a visible population of cells produced by growth on solid medium.

What should sterile media look like before exposure?

Free of visible microbial growth.

What is examined in Period Two of Exercise 6?

Liquid and solid cultures are examined for changes indicating growth.

Why gently shake broth before examining it?

To distribute growth through the liquid so its appearance can be observed.

What does variation in colony appearance suggest?

Different microorganisms may be present.

What is the main purpose of aseptic technique?

Prevent contamination of cultures, the handler/others, and the work environment.

When is the work area disinfected?

Before and after working, and after spills.

What may routine disinfectants fail to destroy?

Endospores.

How hot is an inoculating loop heated?

Until the entire wire is red-hot.

Why cool the loop before taking inoculum?

A hot loop can kill the organisms being transferred.

Where should the loop never be placed?

On the bench/desk.

Are agar plates flamed?

No.

What may be flamed on a culture tube?

The tube mouth, unless an incinerator is used.

Where is the culture-tube cap held?

In the hand holding the loop; never on the bench.

How is an agar slant inoculated?

Bottom-to-top in a zigzag without gouging the agar.

What is clamshelling?

Keeping the plate lid partially open and positioned over the plate while working.

Where is a plate label placed?

On the bottom of the plate, the part containing agar.

Why are plates incubated upside down?

To prevent condensation from spreading organisms.

Can broth alone prove a culture is pure?

Not necessarily.

What is the purpose of streak plating?

To separate cells so isolated colonies can be obtained.

What color is Serratia marcescens in the stated report?

Red.

What color is Micrococcus luteus?

Yellow.

What color is Chromobacterium violaceum?

Purple.

What color is E. coli listed as when included?

Yellow.

Why is dilution used for pure cultures?

To reduce cell density so individual colonies can become separated.

What should be compared between streak and pour plates?

Which method gives the best separation and the distribution of colonies.

How can purity of a subculture be confirmed?

Look for evidence that only the desired organism is present, using the exercise's culture/staining observations.

Why are plates incubated inverted?

To prevent condensation from spreading growth.

What are surface colonies?

Colonies growing at or near the agar surface.

What are subsurface colonies?

Colonies growing within the agar.

Why can surface and subsurface colonies differ?

They experience different oxygen and physical conditions.

What is the purpose of a good smear?

To prepare cells for clear microscopic examination and staining.

Why should a smear be thin?

To allow individual cells and morphology to be seen clearly.

What happens if too many cells are used in a smear?

The smear becomes thick and cells overlap.

What must happen before heat fixation?

The smear must air-dry completely.

Why heat-fix?

To attach cells to the slide and help preserve them during staining.

What can prolonged heating do to a smear?

Distort or damage cells.

What is the purpose of simple staining?

To make cells easier to see and examine their morphology/arrangement.

What type of dye generally stains bacterial cells in a simple stain?

A basic dye.

What are cocci?

Spherical cells.

What are bacilli?

Rod-shaped cells.

What is a vibrio?

A curved/comma-shaped cell.

What is a spirillum?

A rigid spiral-shaped cell.

What is a spirochete?

A thin, flexible spiral-shaped cell.

What are diplococci?

Cocci in pairs.

What are tetrads?

Cocci in groups of four.

What are streptococci?

Cocci in chains.

What are staphylococci?

Cocci in irregular clusters.

What is a palisade arrangement?

Rod-shaped cells arranged side-by-side like a picket fence.

What is pleomorphism?

Variation in cell shape/form within a bacterial population.

What is the purpose of negative staining?

To stain the background so relatively clear cells can be observed.

What does capsule staining reveal?

A capsule may appear as a clear halo around the cell.

What is the purpose of Gram staining?

To differentiate Gram-positive and Gram-negative bacteria and observe morphology.

What is crystal violet?

The primary Gram stain.

What is iodine in Gram staining?

The mordant that helps form the crystal violet-iodine complex.

What is the critical Gram-stain step?

Decolorization.

What color are properly stained Gram-positive cells?

Purple.

What color are Gram-negative cells after counterstaining?

Pink/red.

What is safranin?

The Gram-stain counterstain.

Why can culture age affect Gram staining?

Older cultures can become Gram-variable.

What is Gram-variable?

A culture showing inconsistent Gram reactions.

What does endospore staining detect?

Endospores relative to vegetative cells.

What does acid-fast staining test?

Whether cells retain the primary stain despite acid-alcohol decolorization.

What is an obligate anaerobe?

An organism that cannot tolerate oxygen and grows only when oxygen is absent.

What is an obligate aerobe?

An organism that requires oxygen for growth.

What is a facultative anaerobe?

An organism able to grow with or without oxygen, often better with oxygen.

What is an aerotolerant anaerobe?

An organism that does not use oxygen but tolerates it.

What is a microaerophile?

An organism requiring oxygen at lower-than-atmospheric concentration.

How can an anaerobic jar create an anaerobic atmosphere?

A system removes oxygen; a disposable packet can chemically react with oxygen.

What does a palladium catalyst do in a GasPak system?

It facilitates removal of oxygen by helping hydrogen react with oxygen to form water.

What is Brewer's anaerobic agar used for?

Supporting anaerobic cultivation by reducing/removing oxygen in the medium.

How does an Oxyrase plate work?

It removes oxygen around the culture to support anaerobic growth.

What can cracking of agar indicate?

Gas production.

Which organism demonstrates strong aerobic growth?

Pseudomonas aeruginosa.

Which organism demonstrates anaerobic growth?

Clostridium sporogenes.

Which organism demonstrates a facultative pattern?

Escherichia coli.

What is examined in thioglycollate broth?

The location/pattern of growth along the oxygen gradient.

What colony range is statistically useful?

30-300 colonies per plate.

What does TTC mean?

Too many to count; more than 300 colonies.

What does TFTC mean?

Too few to count; fewer than 30 colonies.

What is a CFU?

A colony-forming unit representing viable cells or cell groups capable of forming a colony under the test conditions.

Why can CFUs be especially applicable to Streptococcus?

Streptococci can occur in chains/groups, so one colony may arise from multiple cells.

Why use serial dilution before plating?

To reduce cell concentration to a countable range.

What volume was used for the described standard-plate adjustment?

0.1 mL.

How do you convert a count based on 0.1 mL to organisms/mL?

Divide the CFU count by 0.1 mL.

What does O.D. represent here?

Optical density/turbidity associated with cells in culture.

Why calibrate O.D. against cell concentration?

The relationship depends on the organism and conditions being tested.

What is plotted for the O.D. exercise?

Optical density versus organism concentration.

What is the maximum O.D. in the linear portion?

Determine it from your actual class graph/data; no numerical value was supplied.

What is the correlation between O.D. and cell number?

Determine it from your actual culture data; no numerical value was supplied.

What is a 1:40 dilution?

1 part culture in a total of 40 parts.