BIOD 171 Microbiology Module 6 Exam
Portage Learning | Actual Exam
100 Questions • Verified Answers • Detailed Rationales
Section 1: Principles of Microbial Control and Sterilization (Physical Methods,
Chemical Agents, & Antimicrobial Evaluation)
Q1: A microbiology student argues that bacteriostatic and bactericidal agents are interchangeable in
immunocompromised patients. Which response best corrects this misconception?
A. Bacteriostatic agents kill bacteria outright, so they are preferred in immunocompromised hosts.
B. Bacteriostatic agents only inhibit replication; bactericidal agents kill, and bactericidal drugs are
preferred when host defenses are impaired. [CORRECT]
C. Both agent types rely entirely on host neutrophils to clear the infection.
D. Bactericidal agents merely arrest growth, making them equivalent to bacteriostatic agents.
Correct Answer: B
Rationale: Bactericidal agents directly kill microbial cells (e.g., beta-lactams, vancomycin), whereas bacteriostatic
agents only inhibit replication (e.g., tetracyclines, chloramphenicol), requiring functional host immunity for final
clearance. Portage Learning BIOD 171 Module 6 emphasizes that in neutropenic or immunocompromised patients,
bactericidal drugs are strongly preferred because host phagocytes cannot reliably finish the job. The distractors
invert definitions or overstate host dependence.
Q2: An autoclave cycle operating at 121 °C and 15 psi for 15 minutes fails to sterilize a load of bone
grafts. The most likely cause consistent with Portage BIOD 171 autoclave principles is:
A. Insufficient pressure (psi is too low to penetrate porous bone).
B. Air remaining in the chamber, preventing saturated steam from contacting the load. [CORRECT]
C. Use of dry-heat parameters instead of moist-heat parameters.
D. Cycle time being too short for any sterilization to occur.
Correct Answer: B
Rationale: Autoclaves sterilize by saturated steam under pressure; trapped air acts as an insulating pocket that
prevents steam condensation on the load surface, leaving cold spots where spores survive. Portage BIOD 171 stresses
air exhaust, steam penetration, and indicator verification (chemical and biological indicators such as Geobacillus
stearothermophilus spores). Pressure alone (A) is irrelevant without saturated steam contact; dry heat (C) is a
different method; 15 min (D) is adequate for routine loads when steam contacts the load.
,Q3: Which parameter set defines standard autoclave sterilization conditions taught in Portage BIOD
171 for surgical instruments?
A. 100 °C, 0 psi, 30 minutes
B. 121 °C, 15 psi, 15 minutes (or 134 °C, 30 psi, 3 minutes for prion risk loads) [CORRECT]
C. 160 °C dry heat, 2 hours
D. 72 °C, 15 seconds pasteurization
Correct Answer: B
Rationale: Standard autoclave sterilization uses saturated steam at 121 °C, 15 psi, for 15 minutes (or 134 °C, 30 psi,
3 min for prion-contaminated loads). Boiling water at 100 °C (A) does not kill spores; dry heat at 160 °C for 2 h (C)
is a separate method for powders/glass; pasteurization (D) only reduces pathogen load, not sterilization.
Q4: A dairy plant uses high-temperature short-time (HTST) pasteurization. Which combination
correctly reflects Portage BIOD 171 pasteurization parameters?
A. 63 °C for 30 minutes (LTLT)
B. 72 °C for 15 seconds (HTST) [CORRECT]
C. 141 °C for 2 seconds (UHT)
D. 100 °C for 10 minutes
Correct Answer: B
Rationale: HTST pasteurization operates at 72 °C for 15 seconds; LTLT (batch) is 63 °C for 30 min; UHT is 141 °C
for 2 s and yields shelf-stable milk. Portage BIOD 171 teaches these to differentiate heat-treatment intensities and
their purposes (pathogen reduction vs. commercial sterility). Option D is boiling, not pasteurization.
Q5: Which microbial structure is most resistant to moist heat, requiring extended autoclave cycles or
prion-specific protocols?
A. Vegetative Staphylococcus cells
B. Escherichia coli endotoxin (LPS)
C. Bacterial endospores (e.g., Bacillus and Clostridium species) [CORRECT]
D. Enveloped viral particles such as influenza
Correct Answer: C
Rationale: Endospores are the most heat-resistant microbial structures, surviving boiling for prolonged periods;
prions are even more resistant and require 134 °C/18 min or NaOH pre-treatment. Portage BIOD 171 uses G.
stearothermophilus spores as the biological indicator for autoclave efficacy. Vegetative bacteria, LPS, and enveloped
viruses are far less heat-resistant.
,Q6: A laboratory needs to sterilize a heat-sensitive antibiotic solution. Which physical method is most
appropriate per Portage BIOD 171 guidelines?
A. Dry-heat oven at 160 °C
B. Membrane filtration through a 0.22 µm pore-size filter [CORRECT]
C. Autoclave at 121 °C for 15 min
D. Pasteurization at 72 °C for 15 s
Correct Answer: B
Rationale: Filtration physically removes microbes without heat, ideal for thermolabile solutions such as antibiotics,
sera, and media. Portage BIOD 171 specifies a 0.22 µm pore size for sterilizing filtration. Dry heat and autoclaving
degrade heat-sensitive antibiotics; pasteurization is not sterilization. Note that viruses smaller than the pore size may
pass, so filtrate is sterilized for bacteria but not always for viruses.
Q7: Ionizing radiation such as gamma rays sterilize medical products by which primary mechanism?
A. Forming pyrimidine dimers that block DNA replication (nonionizing mechanism).
B. Generating hydroxyl radicals and causing strand breaks in DNA. [CORRECT]
C. Disrupting the cytoplasmic membrane lipid bilayer.
D. Denaturing ribosomal proteins, halting translation.
Correct Answer: B
Rationale: Ionizing radiation (gamma, X-ray, electron beam) produces reactive oxygen species that fragment DNA;
it penetrates dense materials and is used for syringes, sutures, and tissue grafts. Nonionizing UV (A) forms thymine
dimers and has poor penetration. Membrane disruption (C) describes detergents; ribosomal denaturation (D)
describes heat or aminoglycosides.
Q8: A nurse asks why 70% ethanol is more effective than 95% ethanol for skin antisepsis. The correct
Portage BIOD 171 explanation is that:
A. 95% ethanol contains more water and thus evaporates too slowly.
B. 70% ethanol has enough water to denature proteins and penetrate cells, whereas 95% dehydrates
cells without adequate protein coagulation. [CORRECT]
C. 70% ethanol has a higher alcohol content than 95% ethanol.
D. 95% ethanol is less flammable and therefore less effective.
Correct Answer: B
Rationale: Alcohols require water to denature proteins; 70% ethanol optimally balances concentration and water
availability for membrane penetration and protein coagulation. 95% ethanol rapidly coagulates surface proteins,
forming a protective barrier that prevents further penetration. Portage BIOD 171 highlights concentration as a
critical factor affecting antimicrobial effectiveness.
, Q9: Which agent is classified as a true sterilant (sporicide) capable of achieving sterilization, not
merely high-level disinfection?
A. 70% isopropyl alcohol
B. Quaternary ammonium compound (benzalkonium chloride)
C. Glutaraldehyde at ≥2% for ≥10 hours (or ethylene oxide gas, vaporized hydrogen peroxide)
[CORRECT]
D. Chlorhexidine gluconate 4% surgical scrub
Correct Answer: C
Rationale: Glutaraldehyde at sufficient concentration and contact time (≥10 h), ethylene oxide gas, vaporized
hydrogen perioxide, and peracetic acid are sterilants that destroy spores. Alcohols, quaternary ammonium
compounds, and chlorhexidine are disinfectants/antiseptics but not sporicidal under routine use. Portage BIOD 171
distinguishes sterilant, high-level disinfectant, intermediate, and low-level categories.
Q10: In the phenol coefficient test, a disinfectant with a coefficient of 5.0 means that:
A. The disinfectant is five times more dilute than phenol.
B. The disinfectant is five times more effective than phenol against the test organism under the same
conditions. [CORRECT]
C. The disinfectant requires five minutes of contact time.
D. The disinfectant kills only Gram-positive bacteria.
Correct Answer: B
Rationale: The phenol coefficient compares a disinfectant's highest effective dilution to phenol's against Salmonella
typhi or Staphylococcus aureus. A coefficient of 5 means the disinfectant is effective at five-fold greater dilution
than phenol. Portage BIOD 161/171 note this is an older, limited assay that does not reflect in-use conditions;
modern methods include use-dilution and disk-diffusion tests.
Q11: In the use-dilution test, stainless steel carriers are contaminated with bacteria, exposed to
disinfectant dilutions, then transferred to recovery medium. A 1:100 dilution showing no growth
indicates:
A. The disinfectant failed completely.
B. That dilution is tuberculocidal.
C. The dilution killed all test organisms on the carrier, indicating effective use concentration.
[CORRECT]
D. The disinfectant must be discarded because dilution is too high.
Correct Answer: C
Rationale: The use-dilution test (AOAC method) is the regulatory standard for confirming that a working dilution
of a disinfectant reliably kills test organisms (S. aureus, P. aeruginosa, S. enterica) on inanimate carriers. No growth
at a given dilution supports the manufacturer's recommended use concentration. Portage BIOD 171 contrasts this
in-use relevance with the phenol coefficient.
Portage Learning | Actual Exam
100 Questions • Verified Answers • Detailed Rationales
Section 1: Principles of Microbial Control and Sterilization (Physical Methods,
Chemical Agents, & Antimicrobial Evaluation)
Q1: A microbiology student argues that bacteriostatic and bactericidal agents are interchangeable in
immunocompromised patients. Which response best corrects this misconception?
A. Bacteriostatic agents kill bacteria outright, so they are preferred in immunocompromised hosts.
B. Bacteriostatic agents only inhibit replication; bactericidal agents kill, and bactericidal drugs are
preferred when host defenses are impaired. [CORRECT]
C. Both agent types rely entirely on host neutrophils to clear the infection.
D. Bactericidal agents merely arrest growth, making them equivalent to bacteriostatic agents.
Correct Answer: B
Rationale: Bactericidal agents directly kill microbial cells (e.g., beta-lactams, vancomycin), whereas bacteriostatic
agents only inhibit replication (e.g., tetracyclines, chloramphenicol), requiring functional host immunity for final
clearance. Portage Learning BIOD 171 Module 6 emphasizes that in neutropenic or immunocompromised patients,
bactericidal drugs are strongly preferred because host phagocytes cannot reliably finish the job. The distractors
invert definitions or overstate host dependence.
Q2: An autoclave cycle operating at 121 °C and 15 psi for 15 minutes fails to sterilize a load of bone
grafts. The most likely cause consistent with Portage BIOD 171 autoclave principles is:
A. Insufficient pressure (psi is too low to penetrate porous bone).
B. Air remaining in the chamber, preventing saturated steam from contacting the load. [CORRECT]
C. Use of dry-heat parameters instead of moist-heat parameters.
D. Cycle time being too short for any sterilization to occur.
Correct Answer: B
Rationale: Autoclaves sterilize by saturated steam under pressure; trapped air acts as an insulating pocket that
prevents steam condensation on the load surface, leaving cold spots where spores survive. Portage BIOD 171 stresses
air exhaust, steam penetration, and indicator verification (chemical and biological indicators such as Geobacillus
stearothermophilus spores). Pressure alone (A) is irrelevant without saturated steam contact; dry heat (C) is a
different method; 15 min (D) is adequate for routine loads when steam contacts the load.
,Q3: Which parameter set defines standard autoclave sterilization conditions taught in Portage BIOD
171 for surgical instruments?
A. 100 °C, 0 psi, 30 minutes
B. 121 °C, 15 psi, 15 minutes (or 134 °C, 30 psi, 3 minutes for prion risk loads) [CORRECT]
C. 160 °C dry heat, 2 hours
D. 72 °C, 15 seconds pasteurization
Correct Answer: B
Rationale: Standard autoclave sterilization uses saturated steam at 121 °C, 15 psi, for 15 minutes (or 134 °C, 30 psi,
3 min for prion-contaminated loads). Boiling water at 100 °C (A) does not kill spores; dry heat at 160 °C for 2 h (C)
is a separate method for powders/glass; pasteurization (D) only reduces pathogen load, not sterilization.
Q4: A dairy plant uses high-temperature short-time (HTST) pasteurization. Which combination
correctly reflects Portage BIOD 171 pasteurization parameters?
A. 63 °C for 30 minutes (LTLT)
B. 72 °C for 15 seconds (HTST) [CORRECT]
C. 141 °C for 2 seconds (UHT)
D. 100 °C for 10 minutes
Correct Answer: B
Rationale: HTST pasteurization operates at 72 °C for 15 seconds; LTLT (batch) is 63 °C for 30 min; UHT is 141 °C
for 2 s and yields shelf-stable milk. Portage BIOD 171 teaches these to differentiate heat-treatment intensities and
their purposes (pathogen reduction vs. commercial sterility). Option D is boiling, not pasteurization.
Q5: Which microbial structure is most resistant to moist heat, requiring extended autoclave cycles or
prion-specific protocols?
A. Vegetative Staphylococcus cells
B. Escherichia coli endotoxin (LPS)
C. Bacterial endospores (e.g., Bacillus and Clostridium species) [CORRECT]
D. Enveloped viral particles such as influenza
Correct Answer: C
Rationale: Endospores are the most heat-resistant microbial structures, surviving boiling for prolonged periods;
prions are even more resistant and require 134 °C/18 min or NaOH pre-treatment. Portage BIOD 171 uses G.
stearothermophilus spores as the biological indicator for autoclave efficacy. Vegetative bacteria, LPS, and enveloped
viruses are far less heat-resistant.
,Q6: A laboratory needs to sterilize a heat-sensitive antibiotic solution. Which physical method is most
appropriate per Portage BIOD 171 guidelines?
A. Dry-heat oven at 160 °C
B. Membrane filtration through a 0.22 µm pore-size filter [CORRECT]
C. Autoclave at 121 °C for 15 min
D. Pasteurization at 72 °C for 15 s
Correct Answer: B
Rationale: Filtration physically removes microbes without heat, ideal for thermolabile solutions such as antibiotics,
sera, and media. Portage BIOD 171 specifies a 0.22 µm pore size for sterilizing filtration. Dry heat and autoclaving
degrade heat-sensitive antibiotics; pasteurization is not sterilization. Note that viruses smaller than the pore size may
pass, so filtrate is sterilized for bacteria but not always for viruses.
Q7: Ionizing radiation such as gamma rays sterilize medical products by which primary mechanism?
A. Forming pyrimidine dimers that block DNA replication (nonionizing mechanism).
B. Generating hydroxyl radicals and causing strand breaks in DNA. [CORRECT]
C. Disrupting the cytoplasmic membrane lipid bilayer.
D. Denaturing ribosomal proteins, halting translation.
Correct Answer: B
Rationale: Ionizing radiation (gamma, X-ray, electron beam) produces reactive oxygen species that fragment DNA;
it penetrates dense materials and is used for syringes, sutures, and tissue grafts. Nonionizing UV (A) forms thymine
dimers and has poor penetration. Membrane disruption (C) describes detergents; ribosomal denaturation (D)
describes heat or aminoglycosides.
Q8: A nurse asks why 70% ethanol is more effective than 95% ethanol for skin antisepsis. The correct
Portage BIOD 171 explanation is that:
A. 95% ethanol contains more water and thus evaporates too slowly.
B. 70% ethanol has enough water to denature proteins and penetrate cells, whereas 95% dehydrates
cells without adequate protein coagulation. [CORRECT]
C. 70% ethanol has a higher alcohol content than 95% ethanol.
D. 95% ethanol is less flammable and therefore less effective.
Correct Answer: B
Rationale: Alcohols require water to denature proteins; 70% ethanol optimally balances concentration and water
availability for membrane penetration and protein coagulation. 95% ethanol rapidly coagulates surface proteins,
forming a protective barrier that prevents further penetration. Portage BIOD 171 highlights concentration as a
critical factor affecting antimicrobial effectiveness.
, Q9: Which agent is classified as a true sterilant (sporicide) capable of achieving sterilization, not
merely high-level disinfection?
A. 70% isopropyl alcohol
B. Quaternary ammonium compound (benzalkonium chloride)
C. Glutaraldehyde at ≥2% for ≥10 hours (or ethylene oxide gas, vaporized hydrogen peroxide)
[CORRECT]
D. Chlorhexidine gluconate 4% surgical scrub
Correct Answer: C
Rationale: Glutaraldehyde at sufficient concentration and contact time (≥10 h), ethylene oxide gas, vaporized
hydrogen perioxide, and peracetic acid are sterilants that destroy spores. Alcohols, quaternary ammonium
compounds, and chlorhexidine are disinfectants/antiseptics but not sporicidal under routine use. Portage BIOD 171
distinguishes sterilant, high-level disinfectant, intermediate, and low-level categories.
Q10: In the phenol coefficient test, a disinfectant with a coefficient of 5.0 means that:
A. The disinfectant is five times more dilute than phenol.
B. The disinfectant is five times more effective than phenol against the test organism under the same
conditions. [CORRECT]
C. The disinfectant requires five minutes of contact time.
D. The disinfectant kills only Gram-positive bacteria.
Correct Answer: B
Rationale: The phenol coefficient compares a disinfectant's highest effective dilution to phenol's against Salmonella
typhi or Staphylococcus aureus. A coefficient of 5 means the disinfectant is effective at five-fold greater dilution
than phenol. Portage BIOD 161/171 note this is an older, limited assay that does not reflect in-use conditions;
modern methods include use-dilution and disk-diffusion tests.
Q11: In the use-dilution test, stainless steel carriers are contaminated with bacteria, exposed to
disinfectant dilutions, then transferred to recovery medium. A 1:100 dilution showing no growth
indicates:
A. The disinfectant failed completely.
B. That dilution is tuberculocidal.
C. The dilution killed all test organisms on the carrier, indicating effective use concentration.
[CORRECT]
D. The disinfectant must be discarded because dilution is too high.
Correct Answer: C
Rationale: The use-dilution test (AOAC method) is the regulatory standard for confirming that a working dilution
of a disinfectant reliably kills test organisms (S. aureus, P. aeruginosa, S. enterica) on inanimate carriers. No growth
at a given dilution supports the manufacturer's recommended use concentration. Portage BIOD 171 contrasts this
in-use relevance with the phenol coefficient.
