Medical Micro Lab Review

What should you assume about all lab specimens?
A. Harmless
B. Infectious
C. Sterile
D. Non-living

B

How long should you scrub your hands during proper handwashing?
A. 10 seconds
B. 15 seconds
C. 20 seconds
D. 30 seconds

C

When should you wash your hands?
A. Before lab only
B. After lab only
C. After removing gloves
D. All of the above

D

Which item is NOT allowed in the lab?
A. Gloves
B. Goggles
C. Lab coat
D. Phone

C

What is the magnification of the ocular lens?
A. 4x
B. 10x
C. 40x
D. 100x

B

Which objective requires oil?
A. 4x
B. 10x
C. 40x
D. 100x

D

Which knob is used for fine detail at high power?
A. Fine focus
B. Coarse focus
C. Stage control
D. Condenser

A

Simple stains use what type of dye?
A. Acidic
B. Neutral
C. Alcohol
D. Basic

D

In a negative stain, what is stained?
A. Cell only
B. Background only
C. Capsule only
D. Both cell and background

B

Why is heat NOT used in negative staining?
A. It kills bacteria
B. It distorts cells
C. It stains the background
D. It removes dye

B

What color are Gram-positive bacteria after staining?
A. Pink
B. Green
C. Clear
D. Purple

D

What causes Gram-negative bacteria to lose the crystal violet stain?
A. Heat
B. Alcohol
C. Iodine
D. Safranin

B

What is a common error in Gram staining?
A. Under-staining
B. Over-decolorizing
C. Using too much iodine
D. Using oil

B

What is the main function of a capsule?
A. Protection from phagocytosis
B. Energy production
C. Movement
D. Reproduction

A

What color are endospores after staining?
A. Green
B. Purple
C. Red
D. Clear

A

Which genera form endospores?
A. E. coli
B. Bacillus
C. Staphylococcus
D. Streptococcus

B

Why do we flame the loop?
A. Heat sample
B. Dry bacteria
C. Add oxygen
D. Sterilize it

D

What is the purpose of streak plating?
A. Grow more bacteria
B. Kill bacteria
C. Color bacteria
D. Isolate colonies

D

What is the purpose of serial dilution?
A. Increase bacteria
B. Change color
C. Reduce concentration
D. Kill bacteria

C

Ideal colony count range:
A. 1–10
B. 10–20
C. 30–300
D. 300–1000

C

What does OCD stand for in SPC?
A. Optical cell density
B. Original cell density
C. Organized colony dilution
D. Observed culture density

B

Blood agar is:
A. Selective
B. Neither
C. Both
D. Differential

D

Beta hemolysis shows:
A. Green color
B. No change
C. Clear zone
D. Black color

C

MSA selects for:
A. Staphylococcus
B. Fungi
C. Gram-negative bacteria
D. Streptococcus

A

Yellow MSA result indicates:
A. No growth
B. Non-fermenter
C. Mannitol fermentation
D. Contamination

C

EMB agar metallic green indicates:
A. Salmonella
B. Staph
C. Shigella
D. E. coli

D

MacConkey agar selects for:
A. Gram-positive
B. Gram-negative
C. Fungi
D. Viruses

B

List 3 pieces of PPE used in the lab.

Lab coat, gloves, goggles

When should you wash your hands?

Before/after lab, after removing gloves, after contamination

Why must all specimens be treated as infectious?

Because they may contain pathogens that can cause infection

Name two functions of the condenser and iris diaphragm.

• Condenser: focuses light on specimen

• Iris diaphragm: controls light intensity

Why do you start with low power?

To easily locate specimen and avoid damaging slide

When is oil immersion used?

With the 100x objective lens

Explain why basic dyes stain bacterial cells.

Bacterial cells are negatively charged, so positively charged (basic) dyes bind to them

What is the result of a negative stain?

Clear cells on a dark background

Why is heat fixing used in simple staining but not negative staining?

Heat fixing kills and adheres cells; negative stain avoids distortion

Explain why Gram-positive bacteria stay purple.

Thick peptidoglycan traps crystal violet dye

What happens during the alcohol step?

Alcohol removes dye from Gram-negative cells

What error can cause false Gram-negative results?

Over-decolorizing

What does a capsule look like after staining?

Clear halo around a stained cell on dark background

Why do bacteria form endospores?

To survive harsh environmental conditions

Describe the color results of an endospore stain.

Spores = green, cells = red

What is aseptic technique?

Sterile handling to prevent contamination

Why is the streak plate method important?

To obtain isolated colonies

What is the goal of serial dilution?

To reduce bacterial concentration

Write the formula for OCD (standard plate count).

OCD = CFU / (Dilution factor x Volume plated in mL)

Why do we use the reciprocal for dilution factor?

Because dilution is expressed as inverse (e.g., 10⁶ instead of 10⁻⁶)

What does hemolysis indicate on blood agar?

Breakdown of red blood cells (hemolysis)

What does yellow color mean on MSA?

Mannitol fermentation (acid production)

How does MacConkey agar select against Gram-positive bacteria?

Bile salts and crystal violet inhibit Gram-positive bacteria

What organism is indicated by a metallic green sheen on EMB?

E. coli

What does a black center on HEA indicate?

Salmonella (H₂S production)