Grand Canyon University
Course Number: BIO 205
Course Title: Microbiology
Exam: Final Exam
Date:2026
A patient is admitted with a high fever, severe headache, and neck stiffness. A lumbar puncture
reveals cloudy cerebrospinal fluid with high protein, low glucose, and many neutrophils. A Gram
stain shows Gram-negative diplococci. Which organism is the most likely cause of this infection?
A. Streptococcus pneumoniae
B. Neisseria meningitidis
C. Haemophilus influenzae
D. Listeria monocytogenes
Answer: B.
Rationale: Neisseria meningitidis is a classic cause of bacterial meningitis in young adults and is
characterized as a Gram-negative diplococcus. The low glucose and high protein levels in the CSF
are indicative of bacterial consumption and metabolic byproducts.
A nurse is caring for an elderly patient who has been on broad-spectrum antibiotics for three
weeks. The patient develops profuse, foul-smelling, watery diarrhea. What is the standard
diagnostic test for the suspected pathogen?
A. Blood culture for systemic bacteremia
B. Stool culture for Salmonella and Shigella
C. Enzyme immunoassay or PCR for Clostridioides difficile toxins
D. Sputum Gram stain for anaerobic bacteria
Answer: C.
1
,Rationale: Long-term antibiotic use disrupts normal gut flora, allowing C. difficile to overgrow and
produce toxins. Testing for the toxin genes or the toxins themselves is the definitive way to
diagnose antibiotic-associated pseudomembranous colitis.
True or False: Endotoxins are primarily associated with the outer membrane of Gram-positive
bacteria and are released only when the cell undergoes lysis.
Answer: False.
Rationale: Endotoxins, specifically Lipid A of the lipopolysaccharide layer, are found in the outer
membrane of Gram-negative bacteria. Gram-positive bacteria lack an outer membrane and instead
produce exotoxins.
Fill in the blank: The process by which a bacterial cell takes up free "naked" DNA from its
surrounding environment and incorporates it into its own genome is known as ________.
Answer: Transformation.
Rationale: Transformation is one of the horizontal gene transfer mechanisms. It is clinically
significant as it allows non-pathogenic bacteria to acquire virulence factors or resistance genes
from dead bacteria in the environment.
A postpartum patient presents with symptoms of a urinary tract infection. The lab reports the
presence of a Gram-positive coccus that is catalase-negative and shows gamma-hemolysis on blood
agar. It is identified as Vancomycin-resistant. What is the most likely genus of this organism?
A. Staphylococcus
B. Streptococcus
C. Enterococcus
D. Micrococcus
Answer: C.
Rationale: Enterococci are typically catalase-negative cocci that often show gamma (non-
hemolytic) patterns. Vancomycin-resistant Enterococcus (VRE) is a significant healthcare-
associated pathogen requiring strict contact precautions.
A nurse needle-sticks herself while drawing blood from a patient with a known chronic viral
infection. The nurse’s blood test later shows the presence of Anti-HBs antibodies but she is
negative for HBsAg and Anti-HBc. How should the nurse interpret these results?
A. She has a chronic Hepatitis B infection.
B. She has an acute Hepatitis B infection.
C. She was successfully vaccinated against Hepatitis B.
2
,D. She recovered from a past Hepatitis B infection naturally.
Answer: C.
Rationale: The Hepatitis B vaccine contains the surface antigen (HBsAg) only. Therefore, a
vaccinated individual will produce Anti-HBs but will lack antibodies to the core antigen (Anti-
HBc), which only appears after exposure to the actual virus.
True or False: Prions are highly resistant to standard sterilization methods like boiling and common
disinfectants, requiring specialized protocols such as autoclaving at higher temperatures with
specific chemical treatments.
Answer: True.
Rationale: Prions are misfolded proteins that lack nucleic acids. They are incredibly stable and
resistant to heat and radiation, making them a significant concern for surgical instrument
sterilization in neurosurgery.
Fill in the blank: When a patient is suspected of having active pulmonary tuberculosis, the nurse
must ensure that a ________ stain is performed on the sputum sample because the causative agent
has a waxy, mycolic acid-rich cell wall.
Answer: Acid-fast (or Ziehl-Neelsen).
Rationale: Mycobacterium tuberculosis does not stain well with a traditional Gram stain due to the
high lipid content in its cell wall. The acid-fast stain allows the carbol fuchsin dye to penetrate and
remain despite decolorization with acid-alcohol.
A patient presents to the clinic with an annular, "bulls-eye" rash known as erythema migrans. They
report a recent hiking trip in the Northeast United States. Which vector-borne bacterium is
responsible for this clinical presentation?
A. Rickettsia rickettsii
B. Borrelia burgdorferi
C. Yersinia pestis
D. Francisella tularensis
Answer: B.
Rationale: Borrelia burgdorferi is the spirochete that causes Lyme disease. It is transmitted to
humans through the bite of an infected Ixodes tick, and the bulls-eye rash is a classic early
diagnostic sign.
A nurse is preparing to administer an aminoglycoside antibiotic. The pharmacist notes that the drug
is bactericidal and works by inhibiting protein synthesis. Which specific bacterial structure does
this class of medication target?
3
, A. Peptidoglycan cell wall
B. 70S Ribosome
C. Plasma membrane
D. DNA Gyrase
Answer: B.
Rationale: Many antibiotics target the prokaryotic 70S ribosome to inhibit protein synthesis.
Aminoglycosides specifically bind to the 30S subunit, leading to mRNA misreading and cell death.
True or False: In a Just Culture framework, a nurse should report a "near miss" medication error
involving a contaminated IV line primarily so the microbiology department can track systemic
failures in aseptic technique.
Answer: True.
Rationale: Just Culture encourages the reporting of errors to identify system flaws. From a
microbiology perspective, tracking contaminated lines helps infection control committees identify
breaches in sterile protocol before they result in widespread HAIs.
Fill in the blank: The specialized structure that some bacteria produce to survive harsh
environmental conditions, such as extreme heat or desiccation, is called an ________.
Answer: Endospore.
Rationale: Genera such as Bacillus and Clostridium produce endospores. These are highly resistant
dormant structures that can persist for years and germinate when conditions become favorable,
posing a challenge for hospital disinfection.
Which of the following describes the mechanism of the "Catalase" test used in the laboratory to
differentiate Staphylococcus from Streptococcus?
A. It determines if the bacteria can ferment glucose.
B. It identifies the presence of an enzyme that breaks down hydrogen peroxide into water and
oxygen.
C. It measures the ability of the bacteria to produce a protective capsule.
D. It detects the presence of cytochrome c oxidase in the electron transport chain.
Answer: B.
Rationale: Staphylococci produce catalase, which causes immediate bubbling when hydrogen
peroxide is added. Streptococci are catalase-negative. This is a foundational step in identifying
Gram-positive cocci.
4
Course Number: BIO 205
Course Title: Microbiology
Exam: Final Exam
Date:2026
A patient is admitted with a high fever, severe headache, and neck stiffness. A lumbar puncture
reveals cloudy cerebrospinal fluid with high protein, low glucose, and many neutrophils. A Gram
stain shows Gram-negative diplococci. Which organism is the most likely cause of this infection?
A. Streptococcus pneumoniae
B. Neisseria meningitidis
C. Haemophilus influenzae
D. Listeria monocytogenes
Answer: B.
Rationale: Neisseria meningitidis is a classic cause of bacterial meningitis in young adults and is
characterized as a Gram-negative diplococcus. The low glucose and high protein levels in the CSF
are indicative of bacterial consumption and metabolic byproducts.
A nurse is caring for an elderly patient who has been on broad-spectrum antibiotics for three
weeks. The patient develops profuse, foul-smelling, watery diarrhea. What is the standard
diagnostic test for the suspected pathogen?
A. Blood culture for systemic bacteremia
B. Stool culture for Salmonella and Shigella
C. Enzyme immunoassay or PCR for Clostridioides difficile toxins
D. Sputum Gram stain for anaerobic bacteria
Answer: C.
1
,Rationale: Long-term antibiotic use disrupts normal gut flora, allowing C. difficile to overgrow and
produce toxins. Testing for the toxin genes or the toxins themselves is the definitive way to
diagnose antibiotic-associated pseudomembranous colitis.
True or False: Endotoxins are primarily associated with the outer membrane of Gram-positive
bacteria and are released only when the cell undergoes lysis.
Answer: False.
Rationale: Endotoxins, specifically Lipid A of the lipopolysaccharide layer, are found in the outer
membrane of Gram-negative bacteria. Gram-positive bacteria lack an outer membrane and instead
produce exotoxins.
Fill in the blank: The process by which a bacterial cell takes up free "naked" DNA from its
surrounding environment and incorporates it into its own genome is known as ________.
Answer: Transformation.
Rationale: Transformation is one of the horizontal gene transfer mechanisms. It is clinically
significant as it allows non-pathogenic bacteria to acquire virulence factors or resistance genes
from dead bacteria in the environment.
A postpartum patient presents with symptoms of a urinary tract infection. The lab reports the
presence of a Gram-positive coccus that is catalase-negative and shows gamma-hemolysis on blood
agar. It is identified as Vancomycin-resistant. What is the most likely genus of this organism?
A. Staphylococcus
B. Streptococcus
C. Enterococcus
D. Micrococcus
Answer: C.
Rationale: Enterococci are typically catalase-negative cocci that often show gamma (non-
hemolytic) patterns. Vancomycin-resistant Enterococcus (VRE) is a significant healthcare-
associated pathogen requiring strict contact precautions.
A nurse needle-sticks herself while drawing blood from a patient with a known chronic viral
infection. The nurse’s blood test later shows the presence of Anti-HBs antibodies but she is
negative for HBsAg and Anti-HBc. How should the nurse interpret these results?
A. She has a chronic Hepatitis B infection.
B. She has an acute Hepatitis B infection.
C. She was successfully vaccinated against Hepatitis B.
2
,D. She recovered from a past Hepatitis B infection naturally.
Answer: C.
Rationale: The Hepatitis B vaccine contains the surface antigen (HBsAg) only. Therefore, a
vaccinated individual will produce Anti-HBs but will lack antibodies to the core antigen (Anti-
HBc), which only appears after exposure to the actual virus.
True or False: Prions are highly resistant to standard sterilization methods like boiling and common
disinfectants, requiring specialized protocols such as autoclaving at higher temperatures with
specific chemical treatments.
Answer: True.
Rationale: Prions are misfolded proteins that lack nucleic acids. They are incredibly stable and
resistant to heat and radiation, making them a significant concern for surgical instrument
sterilization in neurosurgery.
Fill in the blank: When a patient is suspected of having active pulmonary tuberculosis, the nurse
must ensure that a ________ stain is performed on the sputum sample because the causative agent
has a waxy, mycolic acid-rich cell wall.
Answer: Acid-fast (or Ziehl-Neelsen).
Rationale: Mycobacterium tuberculosis does not stain well with a traditional Gram stain due to the
high lipid content in its cell wall. The acid-fast stain allows the carbol fuchsin dye to penetrate and
remain despite decolorization with acid-alcohol.
A patient presents to the clinic with an annular, "bulls-eye" rash known as erythema migrans. They
report a recent hiking trip in the Northeast United States. Which vector-borne bacterium is
responsible for this clinical presentation?
A. Rickettsia rickettsii
B. Borrelia burgdorferi
C. Yersinia pestis
D. Francisella tularensis
Answer: B.
Rationale: Borrelia burgdorferi is the spirochete that causes Lyme disease. It is transmitted to
humans through the bite of an infected Ixodes tick, and the bulls-eye rash is a classic early
diagnostic sign.
A nurse is preparing to administer an aminoglycoside antibiotic. The pharmacist notes that the drug
is bactericidal and works by inhibiting protein synthesis. Which specific bacterial structure does
this class of medication target?
3
, A. Peptidoglycan cell wall
B. 70S Ribosome
C. Plasma membrane
D. DNA Gyrase
Answer: B.
Rationale: Many antibiotics target the prokaryotic 70S ribosome to inhibit protein synthesis.
Aminoglycosides specifically bind to the 30S subunit, leading to mRNA misreading and cell death.
True or False: In a Just Culture framework, a nurse should report a "near miss" medication error
involving a contaminated IV line primarily so the microbiology department can track systemic
failures in aseptic technique.
Answer: True.
Rationale: Just Culture encourages the reporting of errors to identify system flaws. From a
microbiology perspective, tracking contaminated lines helps infection control committees identify
breaches in sterile protocol before they result in widespread HAIs.
Fill in the blank: The specialized structure that some bacteria produce to survive harsh
environmental conditions, such as extreme heat or desiccation, is called an ________.
Answer: Endospore.
Rationale: Genera such as Bacillus and Clostridium produce endospores. These are highly resistant
dormant structures that can persist for years and germinate when conditions become favorable,
posing a challenge for hospital disinfection.
Which of the following describes the mechanism of the "Catalase" test used in the laboratory to
differentiate Staphylococcus from Streptococcus?
A. It determines if the bacteria can ferment glucose.
B. It identifies the presence of an enzyme that breaks down hydrogen peroxide into water and
oxygen.
C. It measures the ability of the bacteria to produce a protective capsule.
D. It detects the presence of cytochrome c oxidase in the electron transport chain.
Answer: B.
Rationale: Staphylococci produce catalase, which causes immediate bubbling when hydrogen
peroxide is added. Streptococci are catalase-negative. This is a foundational step in identifying
Gram-positive cocci.
4
