Test Bank for Microbiology with Diseases by
Taxonomy, 6th Edition by Robert Bauman | Latest
2025/2026 Update | Verified A+
1. A researcher isolates a novel Gram-negative bacterium from a patient with necrotizing fasciitis.
The bacterium is facultatively anaerobic, oxidase-positive, and produces a soluble pigment that
fluoresces under UV light. It is resistant to multiple antibiotics, including carbapenems, due to a
metallo--lactamase. Which of the following is the most likely genus and species of this organism?
A. Pseudomonas aeruginosa
B. Acinetobacter baumannii
C. Stenotrophomonas maltophilia
D. Burkholderia cepacia
Answer: A
Rationale: Pseudomonas aeruginosa is a Gram-negative, facultatively anaerobic, oxidase-positive rod
that produces pyocyanin (a fluorescent pigment) and is intrinsically resistant to many antibiotics due to
efflux pumps and acquired -lactamases, including metallo--lactamases. It is a common cause of
necrotizing fasciitis in immunocompromised patients. Acinetobacter baumannii is oxidase-negative and
non-pigmented; Stenotrophomonas maltophilia is oxidase-negative and non-pigmented; Burkholderia
cepacia is oxidase-positive but does not typically produce a fluorescent pigment and is more associated
with pulmonary infections in cystic fibrosis.
2. In a patient with chronic granulomatous disease (CGD), a deficiency in NADPH oxidase leads to
recurrent infections with certain pathogens. Which of the following pathogens is most likely to
cause a life-threatening infection in this patient, and what is the underlying mechanism?
A. Staphylococcus aureus, due to the organism's ability to survive inside neutrophils via catalase production
B. Streptococcus pneumoniae, due to its polysaccharide capsule that prevents opsonization
C. Candida albicans, due to its ability to form hyphae that evade phagocytosis
D. Mycobacterium tuberculosis, due to its waxy cell wall that resists lysosomal enzymes
Answer: A
Rationale: Patients with CGD have a defective NADPH oxidase, impairing the respiratory burst needed
to kill catalase-positive organisms like Staphylococcus aureus, Serratia marcescens, and Aspergillus.
Catalase degrades the small amounts of hydrogen peroxide that the host can produce, leaving the
pathogen unscathed. Streptococcus pneumoniae and Candida albicans are catalase-negative and thus
less problematic in CGD; Mycobacterium tuberculosis uses other mechanisms to survive but is not the
most characteristic pathogen in CGD.
Page 1
,3. A 45-year-old patient with a history of organ transplantation presents with fever, headache, and
confusion. CSF analysis shows lymphocytic pleocytosis, elevated protein, and normal glucose. MRI
reveals temporal lobe hyperintensity. PCR of CSF is positive for a DNA virus. Which of the
following is the most likely pathogen and its replication strategy?
A. Herpes simplex virus type 1, which establishes latency in trigeminal ganglia and reactivates to cause
encephalitis via lytic replication in neurons
B. Varicella-zoster virus, which causes a primary infection and then reactivates as shingles with CNS
involvement
C. Cytomegalovirus, which establishes latency in mononuclear cells and causes encephalitis in
immunocompromised hosts
D. John Cunningham virus, which causes progressive multifocal leukoencephalopathy in immunocompromised
patients
Answer: A
Rationale: Herpes simplex virus type 1 (HSV-1) is the most common cause of sporadic viral encephalitis
in adults, often involving the temporal lobes. It is a DNA virus that establishes latency in sensory
ganglia and reactivates to cause lytic infection in neurons. The CSF profile (lymphocytic pleocytosis,
normal glucose) and MRI findings are classic. VZV and CMV can cause encephalitis but are less
common and have different presentations; JCV causes demyelination (PML) rather than temporal lobe
involvement.
4. A clinical trial evaluates a new antibiotic that inhibits bacterial topoisomerase IV. Which of the
following statements best explains why this antibiotic is effective against Gram-positive bacteria
but less effective against Gram-negative bacteria?
A. Gram-negative bacteria have an outer membrane that prevents the drug from reaching its target, and they
possess efflux pumps that expel the drug.
B. Gram-positive bacteria have a thicker peptidoglycan layer that traps the drug, increasing its local
concentration.
C. Gram-negative bacteria have topoisomerase IV that is structurally resistant to the drug due to an altered
binding site.
D. Gram-positive bacteria have a single topoisomerase that is more sensitive, while Gram-negative bacteria
have multiple redundant topoisomerases.
Answer: A
Rationale: Topoisomerase IV inhibitors (e.g., fluoroquinolones) are less active against Gram-negative
bacteria primarily because the outer membrane acts as a permeability barrier, and efflux pumps (e.g.,
AcrAB-TolC) actively remove the drug. The target topoisomerase IV is similar in both groups, but access
is limited in Gram-negatives. Option B is incorrect because the peptidoglycan layer does not trap the
drug; it is porous. Option C is not the primary reason; resistance can occur but is not inherent. Option
D is false; both have topoisomerase IV and DNA gyrase.
5. A patient with HIV (CD4 count 50 cells/L) presents with a chronic cough and dyspnea. A chest
X-ray shows bilateral interstitial infiltrates. Sputum induction reveals cysts that stain with
methenamine silver. Which of the following organisms is most likely responsible, and what is its
taxonomic classification?
A. Pneumocystis jirovecii, a fungus that is now classified within the Ascomycota
Page 2
,B. Pneumocystis carinii, a protozoan in the phylum Apicomplexa
C. Aspergillus fumigatus, a fungus in the phylum Ascomycota
D. Histoplasma capsulatum, a dimorphic fungus in the phylum Ascomycota
Answer: A
Rationale: Pneumocystis jirovecii (formerly P. carinii) is a major cause of pneumonia in
immunocompromised patients, especially those with HIV and low CD4 counts. It was originally
classified as a protozoan but molecular analysis placed it within the fungal kingdom, specifically
Ascomycota. It stains with methenamine silver and does not grow on routine fungal culture. The name P.
carinii is now reserved for the rat pathogen; human disease is caused by P. jirovecii. Aspergillus and
Histoplasma have different morphologies and clinical presentations.
6. A microbiologist is studying the regulation of virulence factors in a pathogenic bacterium. She
identifies a two-component regulatory system that, when phosphorylated, upregulates the
expression of a type III secretion system (T3SS). Which of the following is the most likely effect of
mutating the sensor kinase in this system?
A. Constitutive activation of the T3SS, leading to increased secretion of effector proteins
B. Loss of T3SS expression, rendering the bacterium avirulent in a mouse model
C. Overexpression of the response regulator, causing a hypervirulent phenotype
D. No effect on T3SS expression, because the response regulator can autophosphorylate
Answer: B
Rationale: In two-component regulatory systems, the sensor kinase autophosphorylates in response to an
environmental signal and then transfers the phosphate to the response regulator, which activates
transcription of target genes. Mutating the sensor kinase typically prevents the phosphorylation cascade,
so the response regulator remains inactive and target genes (like T3SS) are not expressed. This leads to
loss of virulence. Option A and C would require gain-of-function mutations. Option D is incorrect
because the response regulator requires phosphorylation by the sensor kinase.
7. A 30-year-old patient who recently traveled to Southeast Asia presents with fever, jaundice, and
dark urine. Laboratory findings show elevated bilirubin, elevated liver enzymes, and
hemoglobinuria. A blood smear reveals intracellular parasites in red blood cells. Which of the
following is the most likely diagnosis and the vector involved?
A. Babesiosis, transmitted by Ixodes ticks
B. Malaria (Plasmodium falciparum), transmitted by Anopheles mosquitoes
C. Leptospirosis, transmitted by contact with rodent urine
D. Dengue fever, transmitted by Aedes mosquitoes
Answer: B
Rationale: The presentation of fever, jaundice, dark urine (hemoglobinuria), and intracellular parasites
in RBCs is classic for severe malaria, especially P. falciparum, which can cause hemolysis and
blackwater fever. The vector is the female Anopheles mosquito. Babesiosis also has intraerythrocytic
parasites but typically occurs in the US and Europe, and the vector is Ixodes ticks; it usually causes
milder hemolysis. Leptospirosis and dengue do not show intraerythrocytic parasites.
Page 3
, 8. A patient with cystic fibrosis (CF) develops a chronic lung infection with a mucoid strain of
Pseudomonas aeruginosa. The mucoid phenotype is due to overproduction of alginate. Which of
the following mechanisms explains why mucoid strains are more resistant to opsonophagocytosis?
A. Alginate inhibits complement deposition on the bacterial surface, reducing C3b opsonization.
B. Alginate binds to antibodies, preventing Fc receptor recognition by phagocytes.
C. Alginate induces biofilm formation that physically shields the bacteria from immune cells.
D. Alginate suppresses the respiratory burst of neutrophils by scavenging reactive oxygen species.
Answer: A
Rationale: Alginate, a polysaccharide capsule, inhibits complement activation by binding to complement
components and preventing deposition of C3b on the bacterial surface. This reduces opsonization and
subsequent phagocytosis. While alginate also contributes to biofilm formation, the primary mechanism
for resistance to opsonophagocytosis is complement inhibition. Option B is incorrect; alginate does not
bind antibodies. Option D is not the primary mechanism; alginate is not a potent ROS scavenger.
9. A researcher is studying a novel virus that has a segmented negative-sense RNA genome. The
virus is isolated from a patient with hemorrhagic fever. Which of the following is the most likely
family of this virus, and what is a key characteristic of its replication?
A. Bunyaviridae; replication occurs in the cytoplasm, and the virus utilizes cap-snatching to initiate
transcription.
B. Orthomyxoviridae; replication occurs in the nucleus, and the virus uses a primer-dependent mechanism.
C. Arenaviridae; replication occurs in the cytoplasm, and the virus uses an ambisense coding strategy.
D. Filoviridae; replication occurs in the cytoplasm, and the virus produces a single polyprotein.
Answer: A
Rationale: Bunyaviridae (now part of the order Bunyavirales) have segmented negative-sense RNA
genomes and replicate in the cytoplasm. They use cap-snatching from host mRNAs to prime
transcription. Many cause hemorrhagic fevers (e.g., Hantavirus, Rift Valley fever virus).
Orthomyxoviridae (influenza) have segmented negative-sense RNA but replicate in the nucleus and use
cap-snatching as well; however, the question specifies hemorrhagic fever, which is more typical of
bunyaviruses. Arenaviridae have an ambisense genome, not purely negative-sense. Filoviridae have
non-segmented negative-sense RNA.
10. A patient is diagnosed with a systemic fungal infection. The organism is dimorphic, growing as
a mold at 25°C and as a yeast at 37°C. It is endemic to the Ohio and Mississippi River Valleys.
Which of the following is the most likely species, and what is its primary ecological niche?
A. Histoplasma capsulatum; found in soil enriched with bat or bird droppings
B. Coccidioides immitis; found in alkaline desert soils of the southwestern US
C. Blastomyces dermatitidis; found in moist soil and decaying vegetation in the Great Lakes region
D. Paracoccidioides brasiliensis; found in tropical soils of Central and South America
Answer: A
Rationale: Histoplasma capsulatum is a dimorphic fungus endemic to the Ohio and Mississippi River
Valleys. It grows as a mold in soil (especially with bat or bird guano) and converts to yeast at body
temperature. It causes histoplasmosis, often asymptomatic but can cause disseminated disease.
Coccidioides immitis is endemic to the southwestern US (desert soil). Blastomyces dermatitidis is
endemic to the Great Lakes and Ohio River Valley but is not primarily associated with bat/bird
Page 4
Taxonomy, 6th Edition by Robert Bauman | Latest
2025/2026 Update | Verified A+
1. A researcher isolates a novel Gram-negative bacterium from a patient with necrotizing fasciitis.
The bacterium is facultatively anaerobic, oxidase-positive, and produces a soluble pigment that
fluoresces under UV light. It is resistant to multiple antibiotics, including carbapenems, due to a
metallo--lactamase. Which of the following is the most likely genus and species of this organism?
A. Pseudomonas aeruginosa
B. Acinetobacter baumannii
C. Stenotrophomonas maltophilia
D. Burkholderia cepacia
Answer: A
Rationale: Pseudomonas aeruginosa is a Gram-negative, facultatively anaerobic, oxidase-positive rod
that produces pyocyanin (a fluorescent pigment) and is intrinsically resistant to many antibiotics due to
efflux pumps and acquired -lactamases, including metallo--lactamases. It is a common cause of
necrotizing fasciitis in immunocompromised patients. Acinetobacter baumannii is oxidase-negative and
non-pigmented; Stenotrophomonas maltophilia is oxidase-negative and non-pigmented; Burkholderia
cepacia is oxidase-positive but does not typically produce a fluorescent pigment and is more associated
with pulmonary infections in cystic fibrosis.
2. In a patient with chronic granulomatous disease (CGD), a deficiency in NADPH oxidase leads to
recurrent infections with certain pathogens. Which of the following pathogens is most likely to
cause a life-threatening infection in this patient, and what is the underlying mechanism?
A. Staphylococcus aureus, due to the organism's ability to survive inside neutrophils via catalase production
B. Streptococcus pneumoniae, due to its polysaccharide capsule that prevents opsonization
C. Candida albicans, due to its ability to form hyphae that evade phagocytosis
D. Mycobacterium tuberculosis, due to its waxy cell wall that resists lysosomal enzymes
Answer: A
Rationale: Patients with CGD have a defective NADPH oxidase, impairing the respiratory burst needed
to kill catalase-positive organisms like Staphylococcus aureus, Serratia marcescens, and Aspergillus.
Catalase degrades the small amounts of hydrogen peroxide that the host can produce, leaving the
pathogen unscathed. Streptococcus pneumoniae and Candida albicans are catalase-negative and thus
less problematic in CGD; Mycobacterium tuberculosis uses other mechanisms to survive but is not the
most characteristic pathogen in CGD.
Page 1
,3. A 45-year-old patient with a history of organ transplantation presents with fever, headache, and
confusion. CSF analysis shows lymphocytic pleocytosis, elevated protein, and normal glucose. MRI
reveals temporal lobe hyperintensity. PCR of CSF is positive for a DNA virus. Which of the
following is the most likely pathogen and its replication strategy?
A. Herpes simplex virus type 1, which establishes latency in trigeminal ganglia and reactivates to cause
encephalitis via lytic replication in neurons
B. Varicella-zoster virus, which causes a primary infection and then reactivates as shingles with CNS
involvement
C. Cytomegalovirus, which establishes latency in mononuclear cells and causes encephalitis in
immunocompromised hosts
D. John Cunningham virus, which causes progressive multifocal leukoencephalopathy in immunocompromised
patients
Answer: A
Rationale: Herpes simplex virus type 1 (HSV-1) is the most common cause of sporadic viral encephalitis
in adults, often involving the temporal lobes. It is a DNA virus that establishes latency in sensory
ganglia and reactivates to cause lytic infection in neurons. The CSF profile (lymphocytic pleocytosis,
normal glucose) and MRI findings are classic. VZV and CMV can cause encephalitis but are less
common and have different presentations; JCV causes demyelination (PML) rather than temporal lobe
involvement.
4. A clinical trial evaluates a new antibiotic that inhibits bacterial topoisomerase IV. Which of the
following statements best explains why this antibiotic is effective against Gram-positive bacteria
but less effective against Gram-negative bacteria?
A. Gram-negative bacteria have an outer membrane that prevents the drug from reaching its target, and they
possess efflux pumps that expel the drug.
B. Gram-positive bacteria have a thicker peptidoglycan layer that traps the drug, increasing its local
concentration.
C. Gram-negative bacteria have topoisomerase IV that is structurally resistant to the drug due to an altered
binding site.
D. Gram-positive bacteria have a single topoisomerase that is more sensitive, while Gram-negative bacteria
have multiple redundant topoisomerases.
Answer: A
Rationale: Topoisomerase IV inhibitors (e.g., fluoroquinolones) are less active against Gram-negative
bacteria primarily because the outer membrane acts as a permeability barrier, and efflux pumps (e.g.,
AcrAB-TolC) actively remove the drug. The target topoisomerase IV is similar in both groups, but access
is limited in Gram-negatives. Option B is incorrect because the peptidoglycan layer does not trap the
drug; it is porous. Option C is not the primary reason; resistance can occur but is not inherent. Option
D is false; both have topoisomerase IV and DNA gyrase.
5. A patient with HIV (CD4 count 50 cells/L) presents with a chronic cough and dyspnea. A chest
X-ray shows bilateral interstitial infiltrates. Sputum induction reveals cysts that stain with
methenamine silver. Which of the following organisms is most likely responsible, and what is its
taxonomic classification?
A. Pneumocystis jirovecii, a fungus that is now classified within the Ascomycota
Page 2
,B. Pneumocystis carinii, a protozoan in the phylum Apicomplexa
C. Aspergillus fumigatus, a fungus in the phylum Ascomycota
D. Histoplasma capsulatum, a dimorphic fungus in the phylum Ascomycota
Answer: A
Rationale: Pneumocystis jirovecii (formerly P. carinii) is a major cause of pneumonia in
immunocompromised patients, especially those with HIV and low CD4 counts. It was originally
classified as a protozoan but molecular analysis placed it within the fungal kingdom, specifically
Ascomycota. It stains with methenamine silver and does not grow on routine fungal culture. The name P.
carinii is now reserved for the rat pathogen; human disease is caused by P. jirovecii. Aspergillus and
Histoplasma have different morphologies and clinical presentations.
6. A microbiologist is studying the regulation of virulence factors in a pathogenic bacterium. She
identifies a two-component regulatory system that, when phosphorylated, upregulates the
expression of a type III secretion system (T3SS). Which of the following is the most likely effect of
mutating the sensor kinase in this system?
A. Constitutive activation of the T3SS, leading to increased secretion of effector proteins
B. Loss of T3SS expression, rendering the bacterium avirulent in a mouse model
C. Overexpression of the response regulator, causing a hypervirulent phenotype
D. No effect on T3SS expression, because the response regulator can autophosphorylate
Answer: B
Rationale: In two-component regulatory systems, the sensor kinase autophosphorylates in response to an
environmental signal and then transfers the phosphate to the response regulator, which activates
transcription of target genes. Mutating the sensor kinase typically prevents the phosphorylation cascade,
so the response regulator remains inactive and target genes (like T3SS) are not expressed. This leads to
loss of virulence. Option A and C would require gain-of-function mutations. Option D is incorrect
because the response regulator requires phosphorylation by the sensor kinase.
7. A 30-year-old patient who recently traveled to Southeast Asia presents with fever, jaundice, and
dark urine. Laboratory findings show elevated bilirubin, elevated liver enzymes, and
hemoglobinuria. A blood smear reveals intracellular parasites in red blood cells. Which of the
following is the most likely diagnosis and the vector involved?
A. Babesiosis, transmitted by Ixodes ticks
B. Malaria (Plasmodium falciparum), transmitted by Anopheles mosquitoes
C. Leptospirosis, transmitted by contact with rodent urine
D. Dengue fever, transmitted by Aedes mosquitoes
Answer: B
Rationale: The presentation of fever, jaundice, dark urine (hemoglobinuria), and intracellular parasites
in RBCs is classic for severe malaria, especially P. falciparum, which can cause hemolysis and
blackwater fever. The vector is the female Anopheles mosquito. Babesiosis also has intraerythrocytic
parasites but typically occurs in the US and Europe, and the vector is Ixodes ticks; it usually causes
milder hemolysis. Leptospirosis and dengue do not show intraerythrocytic parasites.
Page 3
, 8. A patient with cystic fibrosis (CF) develops a chronic lung infection with a mucoid strain of
Pseudomonas aeruginosa. The mucoid phenotype is due to overproduction of alginate. Which of
the following mechanisms explains why mucoid strains are more resistant to opsonophagocytosis?
A. Alginate inhibits complement deposition on the bacterial surface, reducing C3b opsonization.
B. Alginate binds to antibodies, preventing Fc receptor recognition by phagocytes.
C. Alginate induces biofilm formation that physically shields the bacteria from immune cells.
D. Alginate suppresses the respiratory burst of neutrophils by scavenging reactive oxygen species.
Answer: A
Rationale: Alginate, a polysaccharide capsule, inhibits complement activation by binding to complement
components and preventing deposition of C3b on the bacterial surface. This reduces opsonization and
subsequent phagocytosis. While alginate also contributes to biofilm formation, the primary mechanism
for resistance to opsonophagocytosis is complement inhibition. Option B is incorrect; alginate does not
bind antibodies. Option D is not the primary mechanism; alginate is not a potent ROS scavenger.
9. A researcher is studying a novel virus that has a segmented negative-sense RNA genome. The
virus is isolated from a patient with hemorrhagic fever. Which of the following is the most likely
family of this virus, and what is a key characteristic of its replication?
A. Bunyaviridae; replication occurs in the cytoplasm, and the virus utilizes cap-snatching to initiate
transcription.
B. Orthomyxoviridae; replication occurs in the nucleus, and the virus uses a primer-dependent mechanism.
C. Arenaviridae; replication occurs in the cytoplasm, and the virus uses an ambisense coding strategy.
D. Filoviridae; replication occurs in the cytoplasm, and the virus produces a single polyprotein.
Answer: A
Rationale: Bunyaviridae (now part of the order Bunyavirales) have segmented negative-sense RNA
genomes and replicate in the cytoplasm. They use cap-snatching from host mRNAs to prime
transcription. Many cause hemorrhagic fevers (e.g., Hantavirus, Rift Valley fever virus).
Orthomyxoviridae (influenza) have segmented negative-sense RNA but replicate in the nucleus and use
cap-snatching as well; however, the question specifies hemorrhagic fever, which is more typical of
bunyaviruses. Arenaviridae have an ambisense genome, not purely negative-sense. Filoviridae have
non-segmented negative-sense RNA.
10. A patient is diagnosed with a systemic fungal infection. The organism is dimorphic, growing as
a mold at 25°C and as a yeast at 37°C. It is endemic to the Ohio and Mississippi River Valleys.
Which of the following is the most likely species, and what is its primary ecological niche?
A. Histoplasma capsulatum; found in soil enriched with bat or bird droppings
B. Coccidioides immitis; found in alkaline desert soils of the southwestern US
C. Blastomyces dermatitidis; found in moist soil and decaying vegetation in the Great Lakes region
D. Paracoccidioides brasiliensis; found in tropical soils of Central and South America
Answer: A
Rationale: Histoplasma capsulatum is a dimorphic fungus endemic to the Ohio and Mississippi River
Valleys. It grows as a mold in soil (especially with bat or bird guano) and converts to yeast at body
temperature. It causes histoplasmosis, often asymptomatic but can cause disseminated disease.
Coccidioides immitis is endemic to the southwestern US (desert soil). Blastomyces dermatitidis is
endemic to the Great Lakes and Ohio River Valley but is not primarily associated with bat/bird
Page 4
