NCLEX Microbiology MCQs – Part 3 (101–150)
Microbiology plays a vital role in nursing and healthcare exams like the NCLEX-RN, NCLEX-PN, and other international medical tests. To help nursing students, medical aspirants, and healthcare professionals, we have carefully designed these NCLEX Microbiology MCQs (101–150). Each question is unique, thoroughly explained, and aligned with high standards of exam preparation.
These practice questions will strengthen your concepts on bacteria, viruses, fungi, parasites, and related infectious diseases—key areas tested in the NCLEX and other nursing board exams. By practicing them regularly, you’ll gain the confidence needed to score higher.
101. Which bacteria is most commonly associated with peptic ulcer disease?
A) Escherichia coli
B) Helicobacter pylori ✅
C) Salmonella typhi
D) Clostridium difficile
Explanation: Helicobacter pylori is strongly linked to peptic ulcers due to its ability to survive in the acidic stomach by producing urease, which neutralizes gastric acid.
102. Which of the following viruses is responsible for causing chickenpox?
A) Epstein-Barr virus
B) Varicella-Zoster virus ✅
C) Human papillomavirus
D) Cytomegalovirus
Explanation: Varicella-Zoster virus (VZV) causes chickenpox (varicella) and can later reactivate to cause shingles (herpes zoster).
103. Which fungus is most likely to cause oral thrush?
A) Aspergillus
B) Candida albicans ✅
C) Cryptococcus
D) Histoplasma
Explanation: Oral thrush is a yeast infection of the mouth caused by Candida albicans. It is common in immunocompromised patients and infants.
104. The Mantoux test is used for the diagnosis of which infection?
A) Syphilis
B) Tuberculosis ✅
C) Malaria
D) Leprosy
Explanation: The Mantoux (tuberculin skin) test detects exposure to Mycobacterium tuberculosis through a delayed-type hypersensitivity reaction.
105. Which of the following bacteria is Gram-positive?
A) Salmonella
B) Staphylococcus aureus ✅
C) Klebsiella
D) Neisseria
Explanation: Staphylococcus aureus is a Gram-positive cocci, whereas Salmonella, Klebsiella, and Neisseria are Gram-negative.
106. Which parasite causes malaria?
A) Trypanosoma brucei
B) Plasmodium species ✅
C) Giardia lamblia
D) Leishmania donovani
Explanation: Malaria is caused by Plasmodium species (P. falciparum, P. vivax, P. malariae, P. ovale), transmitted by the bite of Anopheles mosquitoes.
107. The causative agent of whooping cough is:
A) Bordetella pertussis ✅
B) Haemophilus influenzae
C) Corynebacterium diphtheriae
D) Streptococcus pneumoniae
Explanation: Bordetella pertussis infects the respiratory tract and causes whooping cough (pertussis).
108. Which of the following is a prion disease?
A) Rabies
B) Creutzfeldt-Jakob disease ✅
C) Influenza
D) Mumps
Explanation: Prion diseases are caused by misfolded proteins. Creutzfeldt-Jakob disease (CJD) is a rare but fatal neurodegenerative condition.
109. Which of the following vaccines is a live attenuated vaccine?
A) Polio (Salk)
B) BCG ✅
C) Hepatitis B
D) Tetanus
Explanation: BCG (for tuberculosis) is a live attenuated vaccine derived from Mycobacterium bovis.
110. Which bacterial infection is commonly associated with antibiotic-associated diarrhea?
A) Escherichia coli
B) Clostridium difficile ✅
C) Shigella
D) Vibrio cholerae
Explanation: Clostridium difficile overgrowth occurs after prolonged antibiotic use, leading to pseudomembranous colitis.
111. Which bacterium is the most common cause of urinary tract infections (UTIs)?
A) Klebsiella
B) Escherichia coli ✅
C) Enterococcus
D) Proteus
Explanation: E. coli accounts for ~80% of community-acquired UTIs due to its ability to adhere to urinary tract epithelium.
112. Which viral infection is known as “infectious mononucleosis”?
A) Cytomegalovirus
B) Epstein-Barr virus ✅
C) Hepatitis C virus
D) Adenovirus
Explanation: Epstein-Barr virus (EBV) causes infectious mononucleosis, commonly called the “kissing disease.”
113. Which bacterial infection is diagnosed using the Widal test?
A) Typhoid fever ✅
B) Tuberculosis
C) Syphilis
D) Diphtheria
Explanation: The Widal test detects antibodies against Salmonella typhi, the cause of typhoid fever.
114. Which virus causes acquired immunodeficiency syndrome (AIDS)?
A) Human immunodeficiency virus (HIV) ✅
B) Hepatitis B virus
C) Cytomegalovirus
D) Influenza virus
Explanation: HIV attacks CD4+ T-cells, leading to immune suppression and progression to AIDS.
115. Which fungus causes pneumonia in immunocompromised patients, especially those with HIV/AIDS?
A) Aspergillus
B) Pneumocystis jirovecii ✅
C) Candida albicans
D) Cryptococcus neoformans
Explanation: Pneumocystis jirovecii causes Pneumocystis pneumonia (PCP), a common opportunistic infection in AIDS patients.
116. Which bacterial structure is responsible for antibiotic resistance and horizontal gene transfer?
A) Capsule
B) Plasmid ✅
C) Flagella
D) Endospore
Explanation: Plasmids are extra-chromosomal DNA molecules that carry antibiotic resistance genes.
117. Which bacterium produces botulinum toxin?
A) Clostridium botulinum ✅
B) Clostridium tetani
C) Bacillus anthracis
D) Staphylococcus aureus
Explanation: Clostridium botulinum produces botulinum toxin, one of the most potent toxins, causing flaccid paralysis.
118. Which organism is responsible for malaria relapse due to dormant liver stages?
A) Plasmodium falciparum
B) Plasmodium vivax ✅
C) Plasmodium malariae
D) Plasmodium knowlesi
Explanation: P. vivax (and P. ovale) can remain dormant in the liver as hypnozoites, causing relapses.
119. Which microorganism is detected by the India ink test?
A) Candida
B) Cryptococcus neoformans ✅
C) Aspergillus
D) Histoplasma
Explanation: Cryptococcus neoformans (encapsulated yeast) can be visualized using India ink in cerebrospinal fluid (CSF).
120. Which bacteria cause scarlet fever?
A) Streptococcus pyogenes ✅
B) Staphylococcus aureus
C) Corynebacterium diphtheriae
D) Klebsiella pneumoniae
Explanation: Scarlet fever is caused by Streptococcus pyogenes producing erythrogenic exotoxin.
121. Which microorganism causes gas gangrene?
A) Clostridium perfringens ✅
B) Clostridium tetani
C) Pseudomonas aeruginosa
D) Escherichia coli
Explanation: Clostridium perfringens produces exotoxins leading to gas gangrene (myonecrosis).
122. Which virus causes German measles?
A) Measles virus
B) Rubella virus ✅
C) Parvovirus
D) Influenza virus
Explanation: Rubella virus causes German measles, a mild rash illness but dangerous during pregnancy.
123. Which bacterium causes diphtheria?
A) Bacillus anthracis
B) Corynebacterium diphtheriae ✅
C) Mycobacterium leprae
D) Streptococcus pneumoniae
Explanation: Corynebacterium diphtheriae produces a toxin that inhibits protein synthesis, leading to pseudomembrane formation.
124. Which microorganism is the most common cause of meningitis in newborns?
A) Neisseria meningitidis
B) Group B Streptococcus ✅
C) Haemophilus influenzae
D) Listeria monocytogenes
Explanation: In neonates, Group B Streptococcus (GBS) is the leading cause of meningitis.
125. Which bacteria is commonly associated with food poisoning from rice?
A) Clostridium perfringens
B) Bacillus cereus ✅
C) Salmonella
D) Shigella
Explanation: Bacillus cereus produces toxins in improperly stored cooked rice, leading to vomiting/diarrhea.
126. Which virus is responsible for warts?
A) Papillomavirus ✅
B) Herpes simplex virus
C) Adenovirus
D) Hepatitis virus
Explanation: Human papillomaviruses (HPV) cause warts and are associated with cervical cancer.
127. Which bacteria cause leprosy?
A) Mycobacterium tuberculosis
B) Mycobacterium leprae ✅
C) Treponema pallidum
D) Corynebacterium
Explanation: Mycobacterium leprae infects skin and peripheral nerves, leading to leprosy (Hansen’s disease).
128. Which organism causes amoebic dysentery?
A) Giardia lamblia
B) Entamoeba histolytica ✅
C) Trichomonas vaginalis
D) Plasmodium
Explanation: Entamoeba histolytica causes amoebiasis with bloody diarrhea.
129. Which viral hepatitis is transmitted mainly by the fecal-oral route?
A) Hepatitis A and E ✅
B) Hepatitis B
C) Hepatitis C
D) Hepatitis D
Explanation: HAV and HEV are transmitted by contaminated food/water, unlike HBV and HCV (bloodborne).
130. Which bacteria is most often linked with pneumonia in alcoholics?
A) Streptococcus pneumoniae
B) Klebsiella pneumoniae ✅
C) Pseudomonas aeruginosa
D) Legionella pneumophila
Explanation: Klebsiella pneumoniae causes severe pneumonia with “currant jelly sputum,” especially in alcoholics.
131. Which virus is responsible for shingles?
A) Epstein-Barr virus
B) Varicella-Zoster virus ✅
C) Cytomegalovirus
D) Herpes simplex virus
Explanation: VZV reactivates in dorsal root ganglia, causing shingles (herpes zoster).
132. Which bacterium causes syphilis?
A) Neisseria gonorrhoeae
B) Treponema pallidum ✅
C) Chlamydia trachomatis
D) Haemophilus ducreyi
Explanation: Treponema pallidum is a spirochete that causes syphilis, diagnosed with serologic tests (VDRL, RPR).
133. Which fungal infection is commonly acquired by inhaling spores from bird droppings?
A) Aspergillosis
B) Histoplasmosis ✅
C) Candidiasis
D) Blastomycosis
Explanation: Histoplasma capsulatum is found in soil with bird/bat droppings, causing histoplasmosis.
134. Which parasite causes sleeping sickness?
A) Leishmania
B) Trypanosoma brucei ✅
C) Plasmodium
D) Giardia
Explanation: Trypanosoma brucei (transmitted by tsetse fly) causes African sleeping sickness.
135. Which bacterium is identified by the acid-fast staining method?
A) Escherichia coli
B) Mycobacterium tuberculosis ✅
C) Neisseria gonorrhoeae
D) Staphylococcus aureus
Explanation: Mycobacterium tuberculosis has mycolic acid in its cell wall, requiring Ziehl-Neelsen acid-fast staining.
136. Which viral infection can cause congenital birth defects like deafness and cataracts?
A) Rubella ✅
B) Mumps
C) Influenza
D) Polio
Explanation: Congenital rubella syndrome occurs when Rubella virus infects pregnant women, affecting fetal development.
137. Which bacterium is linked with gastric cancer?
A) Salmonella
B) Helicobacter pylori ✅
C) Shigella
D) Klebsiella
Explanation: Chronic H. pylori infection increases the risk of gastric adenocarcinoma.
138. Which parasite is commonly diagnosed by the “Scotch tape test”?
A) Trichuris trichiura
B) Enterobius vermicularis ✅
C) Ascaris lumbricoides
D) Taenia solium
Explanation: Enterobius vermicularis (pinworm) eggs are detected using the tape test.
139. Which microorganism causes tetanus?
A) Clostridium perfringens
B) Clostridium tetani ✅
C) Bacillus anthracis
D) Staphylococcus epidermidis
Explanation: C. tetani produces tetanospasmin toxin, leading to spastic paralysis.
140. Which bacterium is the main cause of meningitis in adolescents and young adults?
A) Neisseria meningitidis ✅
B) Streptococcus pneumoniae
C) Listeria monocytogenes
D) Haemophilus influenzae
Explanation: Neisseria meningitidis spreads rapidly in close-contact environments like dormitories.
141. Which virus causes rabies?
A) Lyssavirus ✅
B) Filovirus
C) Coronavirus
D) Rhabdovirus
Explanation: Rabies virus (a Lyssavirus from the Rhabdoviridae family) causes fatal encephalitis.
142. Which bacterium is associated with hospital-acquired pneumonia and ventilator infections?
A) Pseudomonas aeruginosa ✅
B) Salmonella typhi
C) Staphylococcus epidermidis
D) Streptococcus pyogenes
Explanation: Pseudomonas aeruginosa thrives in hospital settings, causing ventilator-associated pneumonia.
143. Which fungus causes “valley fever”?
A) Coccidioides immitis ✅
B) Blastomyces
C) Candida
D) Aspergillus
Explanation: Coccidioides immitis causes coccidioidomycosis, also called valley fever, endemic in desert areas.
144. Which bacterium causes cholera?
A) Salmonella enterica
B) Vibrio cholerae ✅
C) Shigella dysenteriae
D) Campylobacter jejuni
Explanation: Vibrio cholerae produces cholera toxin, causing severe watery diarrhea (“rice-water stools”).
145. Which virus causes mumps?
A) Rubella virus
B) Paramyxovirus ✅
C) Adenovirus
D) Coxsackievirus
Explanation: Mumps virus (a paramyxovirus) causes salivary gland swelling and orchitis.
146. Which bacterium is associated with dental caries?
A) Lactobacillus
B) Streptococcus mutans ✅
C) Staphylococcus aureus
D) Neisseria
Explanation: Streptococcus mutans produces acid from sugar metabolism, leading to tooth decay.
147. Which protozoan parasite causes giardiasis?
A) Giardia lamblia ✅
B) Plasmodium vivax
C) Entamoeba histolytica
D) Leishmania
Explanation: Giardia lamblia infects the intestines, causing diarrhea, bloating, and malabsorption.
148. Which bacteria are commonly responsible for otitis media in children?
A) Escherichia coli
B) Streptococcus pneumoniae ✅
C) Neisseria meningitidis
D) Salmonella
Explanation: Streptococcus pneumoniae is the leading cause of middle ear infections in children.
149. Which bacterium causes anthrax?
A) Bacillus anthracis ✅
B) Clostridium perfringens
C) Streptococcus pyogenes
D) Listeria monocytogenes
Explanation: Bacillus anthracis produces toxins causing cutaneous, gastrointestinal, or inhalation anthrax.
150. Which virus causes polio?
A) Enterovirus (Poliovirus) ✅
B) Coronavirus
C) Orthomyxovirus
D) Herpesvirus
Explanation: Poliovirus, an enterovirus, can cause paralysis by infecting motor neurons in the spinal cord.
This completes NCLEX Microbiology MCQs Part 3 (101–150). We’ve provided detailed explanations to ensure you don’t just memorize the answers but understand the underlying concepts.
📌 Next Steps:
- Revise Part 1 (1–50) and Part 2 (51–100) for full coverage.
- Bookmark this page and share it with your fellow nursing aspirants.
With consistency and smart practice, your success in NCLEX and other international nursing exams is within reach! 🌍✨