NCLEX Microbiology MCQs – Part 4 (151–200)
Microbiology is a vital part of NCLEX preparation as it strengthens knowledge about pathogens, infections, and immunity. This post features Part 4 of our NCLEX Microbiology MCQs series (Questions) with answers and explanations, helping nursing and medical students test their skills and clarify concepts.
Each question is crafted to reflect the NCLEX exam pattern, focusing on high-yield areas such as bacteria, viruses, fungi, parasites, and clinical microbiology. With detailed explanations, you will not only identify the correct answers but also understand why they are correct, improving critical thinking for exam day.
151. Which bacterial structure is responsible for the transfer of antibiotic resistance genes?
A) Ribosome
B) Plasmid
C) Capsule
D) Flagella
Correct Answer: B) Plasmid
Explanation: Plasmids are small, circular DNA molecules in bacteria that can carry genes for antibiotic resistance. They can transfer between bacteria through conjugation, making infections harder to treat.
152. Which virus is responsible for both chickenpox and shingles?
A) Herpes simplex virus
B) Varicella-zoster virus
C) Epstein-Barr virus
D) Cytomegalovirus
Correct Answer: B) Varicella-zoster virus
Explanation: Varicella-zoster virus causes chickenpox as the primary infection. Later in life, it can reactivate in nerves to cause shingles (herpes zoster).
153. What is the primary role of bacterial pili?
A) Protein synthesis
B) Genetic transfer
C) Energy production
D) Cell wall formation
Correct Answer: B) Genetic transfer
Explanation: Pili (or fimbriae) are hair-like structures that help bacteria attach to surfaces and play a crucial role in conjugation, where plasmid DNA is transferred between bacteria.
154. Why are Gram-negative bacteria resistant to lysozyme?
A) Thick peptidoglycan layer
B) Outer membrane with lipopolysaccharides
C) Capsule covering
D) Absence of murein
Correct Answer: B) Outer membrane with lipopolysaccharides
Explanation: Gram-negative bacteria have an outer membrane that protects them from lysozyme, which normally breaks down peptidoglycan in Gram-positive bacteria.
155. Which microorganism causes lockjaw (tetanus)?
A) Clostridium tetani
B) Clostridium perfringens
C) Bacillus anthracis
D) Vibrio cholerae
Correct Answer: A) Clostridium tetani
Explanation: Clostridium tetani produces tetanospasmin, a neurotoxin that causes severe muscle spasms and lockjaw.
156. Which staining technique is used to identify Mycobacterium tuberculosis?
A) Gram stain
B) Ziehl-Neelsen stain
C) Capsule stain
D) Giemsa stain
Correct Answer: B) Ziehl-Neelsen stain
Explanation: Mycobacterium tuberculosis has a waxy cell wall rich in mycolic acid, making it acid-fast. Ziehl-Neelsen stain is used to detect acid-fast bacilli.
157. The causative agent of syphilis is:
A) Treponema pallidum
B) Neisseria gonorrhoeae
C) Chlamydia trachomatis
D) Haemophilus ducreyi
Correct Answer: A) Treponema pallidum
Explanation: Syphilis is a sexually transmitted infection caused by the spirochete Treponema pallidum, which cannot be cultured on artificial media.
158. Which microorganism is the leading cause of bacterial pneumonia in adults?
A) Haemophilus influenzae
B) Streptococcus pneumoniae
C) Klebsiella pneumoniae
D) Mycoplasma pneumoniae
Correct Answer: B) Streptococcus pneumoniae
Explanation: Streptococcus pneumoniae is the most common cause of community-acquired pneumonia in adults, identified by its capsule and optochin sensitivity.
159. Which organism causes Lyme disease?
A) Rickettsia rickettsii
B) Treponema pallidum
C) Borrelia burgdorferi
D) Leptospira interrogans
Correct Answer: C) Borrelia burgdorferi
Explanation: Lyme disease is transmitted by Ixodes ticks and caused by Borrelia burgdorferi, leading to erythema migrans (bull’s-eye rash).
160. Which bacterium produces diphtheria toxin?
A) Corynebacterium diphtheriae
B) Bacillus anthracis
C) Clostridium botulinum
D) Listeria monocytogenes
Correct Answer: A) Corynebacterium diphtheriae
Explanation: C. diphtheriae produces diphtheria toxin, an exotoxin that inhibits protein synthesis by inactivating elongation factor 2.
161. Which parasite causes malaria?
A) Giardia lamblia
B) Plasmodium species
C) Trypanosoma cruzi
D) Toxoplasma gondii
Correct Answer: B) Plasmodium species
Explanation: Malaria is caused by Plasmodium (falciparum, vivax, malariae, ovale), transmitted by female Anopheles mosquitoes.
162. Which bacterial toxin causes botulism?
A) Endotoxin
B) Exotoxin A
C) Botulinum neurotoxin
D) Shiga toxin
Correct Answer: C) Botulinum neurotoxin
Explanation: Clostridium botulinum produces a neurotoxin that blocks acetylcholine release, leading to flaccid paralysis.
163. Which virus is responsible for infectious mononucleosis?
A) Cytomegalovirus
B) Epstein-Barr virus
C) Human herpesvirus-6
D) Varicella-zoster virus
Correct Answer: B) Epstein-Barr virus
Explanation: EBV, a member of the herpesvirus family, causes mononucleosis with fever, sore throat, lymphadenopathy, and atypical lymphocytes.
164. What is the primary mode of transmission of hepatitis A virus?
A) Blood transfusion
B) Sexual contact
C) Fecal-oral route
D) Insect bites
Correct Answer: C) Fecal-oral route
Explanation: Hepatitis A virus spreads mainly through contaminated food and water, unlike hepatitis B and C which spread via blood and body fluids.
165. Which organism is the cause of whooping cough?
A) Bordetella pertussis
B) Haemophilus influenzae
C) Klebsiella pneumoniae
D) Mycobacterium tuberculosis
Correct Answer: A) Bordetella pertussis
Explanation: Bordetella pertussis causes whooping cough by producing pertussis toxin, which damages respiratory epithelial cells.
166. Which fungus is associated with pigeon droppings and can cause meningitis?
A) Candida albicans
B) Aspergillus fumigatus
C) Cryptococcus neoformans
D) Histoplasma capsulatum
Correct Answer: C) Cryptococcus neoformans
Explanation: Cryptococcus, an encapsulated yeast, often found in pigeon droppings, causes meningitis especially in immunocompromised patients.
167. Which bacterial enzyme breaks down hydrogen peroxide into water and oxygen?
A) Oxidase
B) Catalase
C) Coagulase
D) Hyaluronidase
Correct Answer: B) Catalase
Explanation: Catalase protects bacteria from oxidative damage by breaking down hydrogen peroxide into water and oxygen bubbles.
168. Which microorganism is associated with peptic ulcer disease?
A) Campylobacter jejuni
B) Helicobacter pylori
C) Vibrio cholerae
D) Salmonella typhi
Correct Answer: B) Helicobacter pylori
Explanation: H. pylori survives in the stomach by producing urease, damaging the gastric mucosa and leading to peptic ulcers and gastric cancer.
169. Which virus causes rabies?
A) Retrovirus
B) Rhabdovirus
C) Flavivirus
D) Togavirus
Correct Answer: B) Rhabdovirus
Explanation: Rabies virus belongs to the Rhabdoviridae family and is transmitted through bites of infected animals, causing fatal encephalitis.
170. Which bacterium causes anthrax?
A) Bacillus subtilis
B) Bacillus anthracis
C) Clostridium botulinum
D) Staphylococcus aureus
Correct Answer: B) Bacillus anthracis
Explanation: Bacillus anthracis, a spore-forming Gram-positive rod, produces anthrax toxin and causes cutaneous, pulmonary, or gastrointestinal anthrax.
171. Which virus causes chickenpox?
A) Cytomegalovirus
B) Varicella-zoster virus
C) Herpes simplex virus
D) Human papillomavirus
Correct Answer: B) Varicella-zoster virus
Explanation: Varicella-zoster virus (VZV), a herpesvirus, causes chickenpox (primary infection) and shingles (reactivation in adulthood).
172. Which microorganism is the most common cause of urinary tract infections (UTIs)?
A) Staphylococcus aureus
B) Escherichia coli
C) Klebsiella pneumoniae
D) Proteus mirabilis
Correct Answer: B) Escherichia coli
Explanation: E. coli, part of the normal gut flora, is the leading cause of UTIs due to its fimbriae that adhere to urinary tract epithelium.
173. Which protozoan causes amoebic dysentery?
A) Giardia lamblia
B) Entamoeba histolytica
C) Trichomonas vaginalis
D) Leishmania donovani
Correct Answer: B) Entamoeba histolytica
Explanation: E. histolytica causes amoebic dysentery with bloody diarrhea and liver abscesses. It spreads via contaminated food and water.
174. Which microorganism causes tuberculosis?
A) Mycobacterium leprae
B) Mycobacterium tuberculosis
C) Mycobacterium avium
D) Nocardia asteroides
Correct Answer: B) Mycobacterium tuberculosis
Explanation: M. tuberculosis, an acid-fast bacillus, spreads via respiratory droplets and causes chronic lung infection with granuloma formation.
175. Which bacterium causes syphilis?
A) Borrelia burgdorferi
B) Treponema pallidum
C) Haemophilus ducreyi
D) Chlamydia trachomatis
Correct Answer: B) Treponema pallidum
Explanation: Syphilis is caused by Treponema pallidum, a spirochete transmitted sexually or congenitally.
176. Which bacterium causes tetanus?
A) Clostridium botulinum
B) Clostridium difficile
C) Clostridium tetani
D) Bacillus anthracis
Correct Answer: C) Clostridium tetani
Explanation: C. tetani produces tetanospasmin, a neurotoxin that blocks inhibitory neurotransmitters, leading to spastic paralysis.
177. Which microorganism causes leprosy?
A) Mycobacterium leprae
B) Mycobacterium avium
C) Mycobacterium tuberculosis
D) Nocardia species
Correct Answer: A) Mycobacterium leprae
Explanation: M. leprae infects skin and peripheral nerves, causing leprosy (Hansen’s disease). It is transmitted by prolonged close contact.
178. Which virus causes AIDS?
A) Hepatitis B virus
B) Human T-cell leukemia virus
C) Human immunodeficiency virus
D) Epstein-Barr virus
Correct Answer: C) Human immunodeficiency virus
Explanation: HIV destroys CD4+ T-cells, leading to AIDS, characterized by opportunistic infections and cancers like Kaposi’s sarcoma.
179. Which parasite causes sleeping sickness?
A) Leishmania donovani
B) Trypanosoma cruzi
C) Trypanosoma brucei
D) Giardia lamblia
Correct Answer: C) Trypanosoma brucei
Explanation: Sleeping sickness (African trypanosomiasis) is caused by Trypanosoma brucei, transmitted by the tsetse fly.
180. Which virus causes measles?
A) Rubella virus
B) Morbillivirus (Paramyxovirus family)
C) Adenovirus
D) Enterovirus
Correct Answer: B) Morbillivirus (Paramyxovirus family)
Explanation: Measles virus causes high fever, cough, Koplik spots, and a maculopapular rash. It spreads via respiratory droplets.
181. Which microorganism causes diphtheria?
A) Corynebacterium diphtheriae
B) Haemophilus influenzae
C) Streptococcus pyogenes
D) Bacillus cereus
Correct Answer: A) Corynebacterium diphtheriae
Explanation: C. diphtheriae produces diphtheria toxin, leading to pseudomembrane formation in the throat and myocarditis.
182. Which bacterium causes cholera?
A) Vibrio cholerae
B) Shigella dysenteriae
C) Salmonella enterica
D) Escherichia coli
Correct Answer: A) Vibrio cholerae
Explanation: Vibrio cholerae causes severe watery diarrhea (“rice-water stools”) by producing cholera toxin, which activates cAMP.
183. Which virus causes polio?
A) Retrovirus
B) Flavivirus
C) Enterovirus (Poliovirus)
D) Rhabdovirus
Correct Answer: C) Enterovirus (Poliovirus)
Explanation: Poliovirus infects motor neurons in the spinal cord, causing paralysis. Widespread vaccination has nearly eradicated polio globally.
184. Which fungus causes thrush?
A) Candida albicans
B) Aspergillus species
C) Cryptococcus neoformans
D) Histoplasma capsulatum
Correct Answer: A) Candida albicans
Explanation: C. albicans causes oral thrush, vaginal yeast infection, and systemic candidiasis, especially in immunocompromised patients.
185. Which organism causes gas gangrene?
A) Staphylococcus aureus
B) Clostridium perfringens
C) Bacillus anthracis
D) Pseudomonas aeruginosa
Correct Answer: B) Clostridium perfringens
Explanation: C. perfringens produces alpha toxin, causing myonecrosis (gas gangrene) with foul-smelling tissue and gas bubbles.
186. Which virus causes German measles (rubella)?
A) Paramyxovirus
B) Rubella virus (Togavirus family)
C) Adenovirus
D) Varicella-zoster virus
Correct Answer: B) Rubella virus (Togavirus family)
Explanation: Rubella virus causes a mild rash illness, but congenital rubella can cause birth defects like cataracts, deafness, and heart disease.
187. Which bacterium is commonly associated with hospital-acquired infections and multidrug resistance?
A) Pseudomonas aeruginosa
B) Escherichia coli
C) Clostridium tetani
D) Listeria monocytogenes
Correct Answer: A) Pseudomonas aeruginosa
Explanation: P. aeruginosa causes ventilator-associated pneumonia, urinary tract infections, and sepsis, especially in hospitalized or immunocompromised patients.
188. Which microorganism causes typhoid fever?
A) Salmonella typhi
B) Shigella sonnei
C) Vibrio cholerae
D) Escherichia coli
Correct Answer: A) Salmonella typhi
Explanation: Typhoid fever is caused by Salmonella typhi, transmitted via contaminated food and water, leading to prolonged fever and abdominal pain.
189. Which virus causes smallpox?
A) Herpes simplex virus
B) Poxvirus (Variola virus)
C) Rubella virus
D) Paramyxovirus
Correct Answer: B) Poxvirus (Variola virus)
Explanation: Variola virus caused smallpox, a deadly disease eradicated by global vaccination in 1980.
190. Which bacterium causes plague?
A) Francisella tularensis
B) Yersinia pestis
C) Brucella abortus
D) Rickettsia prowazekii
Correct Answer: B) Yersinia pestis
Explanation: Yersinia pestis, transmitted by flea bites, caused the historical Black Death. It leads to bubonic, septicemic, or pneumonic plague.
191. Which protozoan causes giardiasis?
A) Entamoeba histolytica
B) Giardia lamblia
C) Cryptosporidium parvum
D) Balantidium coli
Correct Answer: B) Giardia lamblia
Explanation: Giardia causes watery diarrhea with foul-smelling stools. It spreads via contaminated water (hikers’ diarrhea).
192. Which bacterium produces toxic shock syndrome toxin (TSST-1)?
A) Streptococcus pyogenes
B) Staphylococcus aureus
C) Pseudomonas aeruginosa
D) Klebsiella pneumoniae
Correct Answer: B) Staphylococcus aureus
Explanation: S. aureus produces TSST-1, causing toxic shock syndrome with fever, hypotension, and rash.
193. Which virus causes mumps?
A) Paramyxovirus
B) Adenovirus
C) Rubella virus
D) Parvovirus
Correct Answer: A) Paramyxovirus
Explanation: Mumps virus causes parotitis, orchitis, meningitis, and pancreatitis, and spreads through respiratory droplets.
194. Which microorganism causes gonorrhea?
A) Treponema pallidum
B) Neisseria gonorrhoeae
C) Chlamydia trachomatis
D) Haemophilus ducreyi
Correct Answer: B) Neisseria gonorrhoeae
Explanation: N. gonorrhoeae, a Gram-negative diplococcus, causes gonorrhea, presenting with purulent urethritis and pelvic inflammatory disease.
195. Which parasite causes malaria with the most severe form (cerebral malaria)?
A) Plasmodium malariae
B) Plasmodium vivax
C) Plasmodium falciparum
D) Plasmodium ovale
Correct Answer: C) Plasmodium falciparum
Explanation: P. falciparum is the deadliest malaria species, causing cerebral malaria, kidney failure, and severe anemia.
196. Which bacterium is the main cause of bacterial meningitis in newborns?
A) Neisseria meningitidis
B) Group B Streptococcus (Streptococcus agalactiae)
C) Listeria monocytogenes
D) Haemophilus influenzae
Correct Answer: B) Group B Streptococcus (Streptococcus agalactiae)
Explanation: Group B strep is the most common cause of neonatal meningitis, often acquired during childbirth.
197. Which bacterium is responsible for diphtheria-like illness but is not Corynebacterium diphtheriae?
A) Corynebacterium ulcerans
B) Bacillus subtilis
C) Mycobacterium bovis
D) Clostridium perfringens
Correct Answer: A) Corynebacterium ulcerans
Explanation: C. ulcerans produces a toxin similar to diphtheria toxin, leading to pharyngitis and pseudomembrane formation.
198. Which virus causes hemorrhagic fever with renal syndrome?
A) Dengue virus
B) Hantavirus
C) Ebola virus
D) Marburg virus
Correct Answer: B) Hantavirus
Explanation: Hantavirus, transmitted by rodent excreta, causes hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome.
199. Which fungus causes valley fever?
A) Histoplasma capsulatum
B) Coccidioides immitis
C) Blastomyces dermatitidis
D) Cryptococcus neoformans
Correct Answer: B) Coccidioides immitis
Explanation: Coccidioides immitis causes valley fever (coccidioidomycosis), common in desert regions of the Americas.
200. Which bacterium produces enterotoxin that causes food poisoning within hours of eating?
A) Staphylococcus aureus
B) Clostridium botulinum
C) Escherichia coli
D) Salmonella typhi
Correct Answer: A) Staphylococcus aureus
Explanation: S. aureus produces pre-formed enterotoxin that causes rapid-onset food poisoning with vomiting and diarrhea.
NCLEX Microbiology MCQs Part 1 (1–50)
NCLEX Microbiology MCQs Part 2 (51–100)
NCLEX Microbiology MCQs Part 3 (101–150)
This concludes Part 4 of our NCLEX Microbiology MCQs series. With answers and detailed explanations, these questions will help you analyze concepts, identify weak areas, and strengthen exam readiness.
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