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Microbiology — BIOL 271 / BIOL 271
BIOL 271 Module 4: Growth Media & Cultivation 2026/2027
Comprehensive Question Bank
78 NCLEX-Style Questions
Question 1
Which antimicrobial is used in CNA agar to inhibit Gram-negative growth?
A. Colistin
B. Nalidixic Acid
C. Gentamicin
D. Tetracycline
Correct Answer B. Nalidixic Acid
Rationale:
Nalidixic acid is a quinolone antibiotic that inhibits DNA gyrase in Gram-negative bacteria, working
alongside colistin to suppress Gram-negative growth on CNA agar.
Question 2
Another name for the quadrant streak method is:
A. Spread plate method
B. Phase-Dilution method
C. Pour plate method
D. Serial dilution method
Correct Answer B. Phase-Dilution method
Rationale:
The quadrant streak method is also called the phase-dilution method because each successive
streaking phase dilutes the microbial concentration.
, Question 3
What is the primary function of selective media?
A. To differentiate between species based on color change
B. To allow growth of certain microorganisms while inhibiting others
C. To provide extra nutrients for fastidious organisms
D. To count total viable cells
Correct Answer B. To allow growth of certain microorganisms while inhibiting others
Rationale:
Selective media contain inhibitors (e.g., antibiotics, dyes, salts) that suppress unwanted organisms
while permitting target species to grow.
Question 4
Which phase in the quadrant streak method typically contains isolated colonies?
A. Phase 1 (P1)
B. Phase 2 (P2)
C. Phase 3 (P3)
D. Phase 4 (P4)
Correct Answer D. Phase 4 (P4)
Rationale:
Phase 4, being the most dilute, typically yields well-separated individual colonies derived from single
cells.
Question 5
Which type of hemolysis is characterized by a clear zone of complete lysis around colonies?
A. Alpha hemolysis
B. Beta hemolysis
C. Gamma hemolysis
D. Delta hemolysis
Correct Answer B. Beta hemolysis
Rationale:
Beta hemolysis is the complete lysis of red blood cells, producing a clear, transparent zone around
the colony, typical of Streptococcus pyogenes.
, Question 6
What is a sterile loop used for in microbiology?
A. To measure temperature
B. To transfer and spread microorganisms during plating
C. To sterilize the work surface
D. To incubate cultures
Correct Answer B. To transfer and spread microorganisms during plating
Rationale:
A sterile loop is a common tool for transferring and streaking microorganisms onto agar plates,
allowing for isolation and pure culture techniques.
Question 7
What are non-pathogenic microorganisms?
A. Microorganisms that always cause disease
B. Microorganisms that do not typically cause disease
C. Microorganisms that only grow at 37°C
D. Microorganisms that cannot be cultured
Correct Answer B. Microorganisms that do not typically cause disease
Rationale:
Non-pathogenic organisms are harmless to healthy hosts and often serve beneficial roles, such as
normal flora or probiotic species.
Microbiology — BIOL 271 / BIOL 271
BIOL 271 Module 4: Growth Media & Cultivation 2026/2027
Comprehensive Question Bank
78 NCLEX-Style Questions
Question 1
Which antimicrobial is used in CNA agar to inhibit Gram-negative growth?
A. Colistin
B. Nalidixic Acid
C. Gentamicin
D. Tetracycline
Correct Answer B. Nalidixic Acid
Rationale:
Nalidixic acid is a quinolone antibiotic that inhibits DNA gyrase in Gram-negative bacteria, working
alongside colistin to suppress Gram-negative growth on CNA agar.
Question 2
Another name for the quadrant streak method is:
A. Spread plate method
B. Phase-Dilution method
C. Pour plate method
D. Serial dilution method
Correct Answer B. Phase-Dilution method
Rationale:
The quadrant streak method is also called the phase-dilution method because each successive
streaking phase dilutes the microbial concentration.
, Question 3
What is the primary function of selective media?
A. To differentiate between species based on color change
B. To allow growth of certain microorganisms while inhibiting others
C. To provide extra nutrients for fastidious organisms
D. To count total viable cells
Correct Answer B. To allow growth of certain microorganisms while inhibiting others
Rationale:
Selective media contain inhibitors (e.g., antibiotics, dyes, salts) that suppress unwanted organisms
while permitting target species to grow.
Question 4
Which phase in the quadrant streak method typically contains isolated colonies?
A. Phase 1 (P1)
B. Phase 2 (P2)
C. Phase 3 (P3)
D. Phase 4 (P4)
Correct Answer D. Phase 4 (P4)
Rationale:
Phase 4, being the most dilute, typically yields well-separated individual colonies derived from single
cells.
Question 5
Which type of hemolysis is characterized by a clear zone of complete lysis around colonies?
A. Alpha hemolysis
B. Beta hemolysis
C. Gamma hemolysis
D. Delta hemolysis
Correct Answer B. Beta hemolysis
Rationale:
Beta hemolysis is the complete lysis of red blood cells, producing a clear, transparent zone around
the colony, typical of Streptococcus pyogenes.
, Question 6
What is a sterile loop used for in microbiology?
A. To measure temperature
B. To transfer and spread microorganisms during plating
C. To sterilize the work surface
D. To incubate cultures
Correct Answer B. To transfer and spread microorganisms during plating
Rationale:
A sterile loop is a common tool for transferring and streaking microorganisms onto agar plates,
allowing for isolation and pure culture techniques.
Question 7
What are non-pathogenic microorganisms?
A. Microorganisms that always cause disease
B. Microorganisms that do not typically cause disease
C. Microorganisms that only grow at 37°C
D. Microorganisms that cannot be cultured
Correct Answer B. Microorganisms that do not typically cause disease
Rationale:
Non-pathogenic organisms are harmless to healthy hosts and often serve beneficial roles, such as
normal flora or probiotic species.
