Practice Test Final Exam

1. The primary goal of the Tiny Earth project is to:
A. Discover antibiotic-resistant organisms
B. Discover antibiotic-producing organisms
C. Create new synthetic antibiotics
D. Identify pathogenic soil bacteria

B – Discover antibiotic-producing organisms

2. Why is TSA + cyclohexamide used when plating soil?
A. Promotes gram-positive growth
B. Inhibits fungal growth
C. Selects for anaerobes
D. Enhances antibiotic production

B – Inhibits fungal growth

3. Which of the following describes “secondary metabolism”?
A. Processes needed for survival
B. Antibiotic production pathways activated under stress
C. DNA replication
D. Fermentation of sugars

B – Antibiotic pathways activated under stress

4. Why are serial dilutions required for soil enumeration?
A. To increase bacterial numbers
B. To obtain countable plates
C. To isolate pure cultures
D. To improve oxygen availability

B – To obtain countable plates

5. A countable plate must have how many colonies?
A. 10–100
B. 50–500
C. 30–300
D. 100–3000

C. 30–300

6. Which organism is a NOT a SAFE relative used in ESKAPE screening?
A. Pseudomonas aeruginosa
B. Staphylococcus aureus
C. Enterococcus raffinosus
D. Acinetobacter baumannii

C. Enterococcus raffinosus

7. What is the purpose of the patch plate in Tiny Earth?
A. To isolate anaerobic bacteria
B. To maintain permanent copies of isolates
C. To test for indole
D. To perform Gram stains

B. To maintain permanent copies of isolates

8. MacConkey Agar selects for:
A. Gram-positive organisms
B. Gram-negative organisms
C. Fungi
D. Acid-fast bacteria

B – Gram-negative organisms

9. Pink colonies on MAC indicate:
A. Lactose fermentation
B. Non-lactose fermentation
C. H₂S production
D. Glucose fermentation only

A – Lactose fermentation

10. EMB agar showing a green metallic sheen indicates:
A. Salmonella
B. Klebsiella
C. E. coli
D. Proteus

C. E. coli

11. Black precipitate on HEA indicates:
A. Lactose fermentation
B. Urease production
C. H₂S production
D. Citrate usage

C – H₂S production

12. MSA turns yellow when the organism:
A. Is gram-negative
B. Ferments mannitol
C. Produces catalase
D. Uses citrate

B – Mannitol fermentation

13. BEA becomes black when:
A. Mannitol is fermented
B. Esculin is hydrolyzed
C. Indole is produced
D. Casein is degraded

B – Esculin hydrolysis

14. Which reagent is used for the indole test?
A. Nitrate A/B
B. Ferric chloride
C. Kovac’s reagent
D. Crystal violet

C – Kovac’s reagent

15. A yellow PR broth indicates:
A. Protein hydrolysis
B. Acid production
C. H₂S production
D. Ammonia formation

B. Acid production

16. A bubble in the Durham tube means:
A. Indole positive
B. Gas production
C. Negative fermentation
D. Nitrate reduction

B – Gas production

17. Citrate-positive organisms appear:
A. Pink
B. Purple
C. Blue
D. Red

C – Blue

18. Gelatinase-positive cultures appear:
A. Solid
B. Liquid
C. Black
D. Cloudy

B – Liquid

19. A red MR test means:
A. Mixed acid fermentation
B. Butanediol fermentation
C. No fermentation
D. H₂S production

A – Mixed acid fermentation

20. VP detects:
A. Lactic acid
B. Acetoin
C. Ammonia
D. Urease activity

B. Acetoin

21. K/A result meaning:
A. Glucose only
B. Lactose only
C. All three sugars fermented
D. No sugars fermented

A. Glucose only

A/A result:
A. Glucose only
B. Glucose + lactose and/or sucrose
C. No fermentation
D. H₂S only

B – Glucose + lactose/sucrose

Black butt in TSIA means:
A. Glucose only
B. H₂S produced
C. Lactose fermentation
D. No acid

B – H₂S produced

Cracks or lifting in TSIA mean:
A. H₂S production
B. Gas production
C. No fermentation
D. MR-positive

B – Gas production

Gram-positive bacteria appear:
A. Pink
B. Purple
C. Green
D. Clear

B – Purple

Gram-negative bacteria have:
A. Thick peptidoglycan
B. Lipopolysaccharide outer membrane
C. No cell wall
D. Mycolic acid

B – Lipopolysaccharide outer membrane

Cocci are:
A. Rod-shaped
B. Spherical
C. Spiral
D. Filamentous

B – Spherical

A Gram-negative rod most closely matches which species?
A. Staphylococcus
B. Corynebacterium
C. E. coli
D. Micrococcus

C. E. coli

The agar used for KB testing is:
A. TSA
B. MSA
C. Mueller-Hinton
D. EMB

C – Mueller-Hinton agar

The zone of inhibition is measured in:
A. Millimeters
B. Centimeters
C. Inches
D. Percentages

A – Millimeters

A small zone of inhibition indicates:
A. Sensitivity
B. Resistance
C. Contamination
D. H₂S production

B – Resistance

The first step in identifying an unknown is:
A. Catalase test
B. Gram stain
C. Plate count
D. MSA

B – Gram stain

SIM can test for:
A. Motility
B. Indole
C. H₂S
D. All of the above

D – All of the above

If EMB shows no growth, the organism is likely:
A. Gram-positive
B. Gram-negative
C. fastidious
D. Halophilic

A – Gram-positive

Which test differentiates lactose fermenters?
A. BEA
B. EMB
C. SIM
D. Citrate

B – EMB

Plated 0.1 mL of a 10⁻³ dilution and counted 120 colonies. CFU/mL?
A. 1.2 × 10⁴
B. 1.2 × 10⁵
C. 1.2 × 10⁶
D. 1.2 × 10⁷

C. 1.2 × 10⁶

Plate with 15 colonies is:
A. Countable
B. TNTC
C. TLTC
D. Contaminated

C – TLTC

Tube 1 in a 10-fold dilution series contains:
A. 10⁰
B. 10⁻¹
C. 10⁻²
D. 10⁻³

B – 10⁻¹

Purpose of quadrant streaking:
A. Count bacteria
B. Isolate pure colonies
C. Test fermentation
D. Perform Gram stains

B – Isolate pure colonies

Why flame sterilize the loop between quadrants?
A. Heat fix
B. Prevent spreading too many cells
C. Increase growth rate
D. Dry the plate

B – Prevent too many cells from spreading

What happens if the ESKAPE lawn does not dry before patching?
A. No zones form
B. Lawn smears and results are unclear
C. Bacteria die
D. Patch fails to grow

B – Lawn smears, results unclear

A patch showing a large zone of clearing indicates:
A. Fermentation
B. Antibiotic production
C. No growth
D. Contamination

B – Antibiotic production

Nitrate → Nitrite indicates:
A. Urease
B. Nitrate reduction
C. Motility
D. Indole

B – Nitrate reduction

Catalase-positive organisms produce:
A. Red pigment
B. Bubbles
C. Green colonies
D. Indole

B – Bubbles

Urease-positive cultures turn:
A. Green
B. Pink
C. Black
D. Blue

B – Pink

Organism is Gram-positive, MSA yellow, catalase positive, beta-hemolytic. Identity?
A. S. epidermidis
B. S. aureus
C. Enterococcus
D. Bacillus subtilis

B. S. aureus

Gram-negative rod, EMB green sheen, PR lac yellow, gas positive:
A. Shigella
B. Salmonella
C. Klebsiella
D. E. coli

D. E. coli

Gram-negative rod, HEA black center, TSIA K/A H₂S+:
A. Salmonella
B. Shigella
C. Pseudomonas
D. E. coli

A. Salmonella

Gram-positive rod, BEA negative, catalase positive, gamma hemolytic:
A. Corynebacterium spp.
B. Enterococcus
C. Bacillus
D. Streptococcus

A. Corynebacterium spp.

Which test confirms mixed acid fermentation?
A. VP
B. SIM
C. MR
D. Gelatinase

C. MR

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

1. What is the Gram reaction of the organism?
A. Gram-positive
B. Gram-negative

B – Gram-negative

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

2. Is the organism a lactose fermenter?
A. Yes
B. No

B – No

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

3. TSIA K/A tells you it ferments:
A. Glucose only
B. All sugars
C. Lactose only

A – Glucose only

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

4. Lack of motility would rule out which organism?
A. Salmonella
B. Shigella
C. E. coli
D. Pseudomonas

A. Salmonella

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

5. HEA with no black precipitate indicates:
A. H₂S positive
B. H₂S negative

B – H₂S negative

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

6. EMB colorless means the organism is:
A. Lac+
B. Lac–

B – Lac–

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

7. Based on results, the most likely organism is:
A. Shigella
B. Salmonella
C. E. coli
D. Proteus

A. Shigella

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

What is the selective agent in MAC?
A. Salt
B. Bile salts + crystal violet
C. Phenylethanol
D. Ferric ammonium citrate

B – Bile salts + crystal violet

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

What is the differential component in TSIA?
A. Sugars
B. Urea
C. Indole
D. Catalase

A – Sugars

Case Scenario

A patient presents with abdominal cramping and diarrhea.
A stool sample is processed in the microbiology lab.
You isolate a Gram-negative rod.

Tests performed:

• MAC: colorless colonies

• EMB: no sheen, colorless

• HEA: green colonies, NO black precipitate

• TSIA: K/A, no gas, no H₂S

• SIM: motility negative, indole negative, no H₂S

• Urease: negative

• Citrate: negative

Which disease is most consistent with the organism identified?
A. Typhoid fever
B. Bacillary dysentery
C. UTIs
D. Hospital pneumonia

B – Bacillary dysentery