NCLEX Microbiology MCQs – Part 2 (51–70)

Microbiology is one of the most crucial areas in nursing exams like the NCLEX, as it directly relates to infection control, patient care, and clinical safety. In this Part 2 (51–100) of NCLEX Microbiology MCQs, we bring you carefully crafted multiple-choice questions along with detailed explanations. These questions cover bacteria, viruses, fungi, and parasites commonly tested in nursing and medical exams.

By practicing these MCQs, you will not only strengthen your theoretical knowledge but also improve your clinical reasoning skills. Whether you are a nursing student in the USA, Canada, UK, Australia, or preparing for other global nursing exams, these microbiology practice questions will be your trusted resource.

Question 51

Which microorganism causes gas gangrene?

A) Clostridium botulinum
B) Clostridium tetani
C) Clostridium perfringens
D) Bacillus anthracis

Answer: C) Clostridium perfringens
Explanation: Gas gangrene is caused by Clostridium perfringens, an anaerobic, spore-forming bacterium that releases exotoxins.

Question 52

Which bacterial structure is responsible for adherence to host cells?

A) Capsule
B) Pili (fimbriae)
C) Flagella
D) Endospore

Answer: B) Pili (fimbriae)
Explanation: Pili enable bacteria to attach to host tissues, playing a key role in pathogenesis.

Question 53

Which virus causes rabies?

A) Lyssavirus
B) Retrovirus
C) Rhabdovirus
D) Orthomyxovirus

Answer: C) Rhabdovirus
Explanation: Rabies virus belongs to the Rhabdoviridae family, transmitted via bites of infected animals.

Question 54

Which microorganism causes tetanus?

A) Clostridium tetani
B) Clostridium perfringens
C) Bacillus anthracis
D) Pseudomonas aeruginosa

Answer: A) Clostridium tetani
Explanation: C. tetani produces tetanospasmin, a neurotoxin that blocks inhibitory neurotransmitters, causing muscle spasms.

Question 55

Which disease is caused by Haemophilus influenzae?

A) Meningitis
B) Tuberculosis
C) Scarlet fever
D) Whooping cough

Answer: A) Meningitis
Explanation: H. influenzae type b is a major cause of bacterial meningitis in children before widespread vaccination.

Question 56

Which parasite causes kala-azar (visceral leishmaniasis)?

A) Giardia lamblia
B) Leishmania donovani
C) Plasmodium falciparum
D) Toxoplasma gondii

Answer: B) Leishmania donovani
Explanation: Kala-azar is a protozoan infection spread by sandflies, caused by Leishmania donovani.

Question 57

Which microorganism is used in the production of yogurt?

A) Lactobacillus bulgaricus
B) E. coli
C) Streptococcus pneumoniae
D) Bacillus subtilis

Answer: A) Lactobacillus bulgaricus
Explanation: Yogurt is produced using Lactobacillus bulgaricus and Streptococcus thermophilus in fermentation.

Question 58

Which bacterium is known as “flesh-eating bacteria”?

A) Staphylococcus aureus
B) Streptococcus pyogenes
C) Pseudomonas aeruginosa
D) Klebsiella pneumoniae

Answer: B) Streptococcus pyogenes
Explanation: Necrotizing fasciitis is caused by Streptococcus pyogenes, releasing toxins that destroy soft tissues.

Question 59

Which microorganism causes African river blindness?

A) Onchocerca volvulus
B) Wuchereria bancrofti
C) Trichinella spiralis
D) Loa loa

Answer: A) Onchocerca volvulus
Explanation: Onchocerciasis is transmitted by blackflies carrying Onchocerca volvulus larvae.

Question 60

Which of the following is a retrovirus?

A) Influenza virus
B) Hepatitis B virus
C) HIV
D) Measles virus

Answer: C) HIV
Explanation: HIV is a retrovirus that uses reverse transcriptase to convert its RNA into DNA inside host cells.

Question 61

Which bacterium is responsible for typhoid fever?

A) Salmonella typhi
B) Shigella dysenteriae
C) Vibrio cholerae
D) E. coli

Answer: A) Salmonella typhi
Explanation: Typhoid fever is caused by Salmonella typhi, transmitted via contaminated food or water.

Question 62

Which fungus causes cryptococcosis?

A) Candida albicans
B) Cryptococcus neoformans
C) Aspergillus fumigatus
D) Histoplasma capsulatum

Answer: B) Cryptococcus neoformans
Explanation: C. neoformans is an encapsulated yeast that causes meningitis, especially in AIDS patients.

Question 63

Which viral disease is transmitted by Aedes mosquitoes?

A) Yellow fever
B) Rabies
C) Polio
D) Smallpox

Answer: A) Yellow fever
Explanation: Aedes mosquitoes transmit yellow fever, dengue, Zika, and chikungunya viruses.

Question 64

Which bacterium produces diphtheria toxin?

A) Corynebacterium diphtheriae
B) Bacillus anthracis
C) Pseudomonas aeruginosa
D) Bordetella pertussis

Answer: A) Corynebacterium diphtheriae
Explanation: C. diphtheriae produces diphtheria toxin, leading to pseudomembrane formation in the throat.

Question 65

Which disease is caused by Plasmodium falciparum?

A) Sleeping sickness
B) Kala-azar
C) Malaria
D) Filariasis

Answer: C) Malaria
Explanation: P. falciparum is the most deadly species of Plasmodium, causing cerebral malaria.

Question 66

Which bacteria are spirochetes?

A) Treponema, Borrelia, Leptospira
B) E. coli, Salmonella, Shigella
C) Staphylococcus, Streptococcus
D) Bacillus, Clostridium

Answer: A) Treponema, Borrelia, Leptospira
Explanation: Spirochetes are spiral-shaped bacteria responsible for syphilis, Lyme disease, and leptospirosis.

Question 67

Which bacterium causes cholera?

A) Shigella dysenteriae
B) Vibrio cholerae
C) Salmonella enterica
D) Campylobacter jejuni

Answer: B) Vibrio cholerae
Explanation: Cholera is caused by V. cholerae, leading to severe watery diarrhea.

Question 68

Which test is used to diagnose tuberculosis?

A) ELISA
B) Mantoux test (PPD)
C) Widal test
D) VDRL test

Answer: B) Mantoux test (PPD)
Explanation: The Mantoux test (tuberculin skin test) detects prior exposure to Mycobacterium tuberculosis.

Question 69

Which virus causes measles?

A) Rubella virus
B) Morbillivirus
C) Adenovirus
D) Varicella-zoster virus

Answer: B) Morbillivirus
Explanation: Measles virus belongs to the Paramyxoviridae family, causing rash, fever, and cough.

Question 70

Which microorganism is the cause of syphilis?

A) Treponema pallidum
B) Neisseria gonorrhoeae
C) Chlamydia trachomatis
D) Haemophilus ducreyi

Answer: A) Treponema pallidum
Explanation: Syphilis is caused by Treponema pallidum, a spiral-shaped spirochete bacterium.

Question 71

Which bacterium causes Lyme disease?

A) Borrelia burgdorferi
B) Treponema pallidum
C) Rickettsia rickettsii
D) Chlamydia trachomatis

Answer: A) Borrelia burgdorferi
Explanation: Lyme disease is a tick-borne illness caused by Borrelia burgdorferi, leading to rash and arthritis.

Question 72

Which microorganism causes whooping cough?

A) Bordetella pertussis
B) Haemophilus influenzae
C) Mycobacterium tuberculosis
D) Corynebacterium diphtheriae

Answer: A) Bordetella pertussis
Explanation: B. pertussis infects the respiratory tract and produces toxins causing severe coughing fits.

Question 73

Which bacterium is responsible for leprosy?

A) Mycobacterium leprae
B) Mycobacterium bovis
C) Mycobacterium tuberculosis
D) Nocardia asteroides

Answer: A) Mycobacterium leprae
Explanation: Leprosy (Hansen’s disease) is caused by M. leprae, affecting skin and peripheral nerves.

Question 74

Which microorganism causes anthrax?

A) Bacillus anthracis
B) Bacillus cereus
C) Clostridium botulinum
D) Staphylococcus aureus

Answer: A) Bacillus anthracis
Explanation: Anthrax is caused by B. anthracis, a spore-forming bacterium affecting skin, lungs, and gut.

Question 75

Which virus causes chickenpox?

A) Varicella-zoster virus
B) Rubella virus
C) Morbillivirus
D) Cytomegalovirus

Answer: A) Varicella-zoster virus
Explanation: Chickenpox is caused by VZV, which can later reactivate as shingles (herpes zoster).

Question 76

Which protozoan parasite causes amoebic dysentery?

A) Entamoeba histolytica
B) Giardia lamblia
C) Trichomonas vaginalis
D) Cryptosporidium parvum

Answer: A) Entamoeba histolytica
Explanation: Amoebiasis is caused by E. histolytica, transmitted via contaminated food and water.

Question 77

Which microorganism causes trachoma (leading cause of blindness)?

A) Chlamydia trachomatis
B) Neisseria gonorrhoeae
C) Staphylococcus aureus
D) Treponema pallidum

Answer: A) Chlamydia trachomatis
Explanation: Chronic infection with C. trachomatis leads to trachoma, a preventable cause of blindness.

Question 78

Which bacterium causes gonorrhea?

A) Neisseria gonorrhoeae
B) Chlamydia trachomatis
C) Treponema pallidum
D) Haemophilus ducreyi

Answer: A) Neisseria gonorrhoeae
Explanation: Gonorrhea is a sexually transmitted infection caused by N. gonorrhoeae.

Question 79

Which parasite causes sleeping sickness?

A) Trypanosoma brucei
B) Plasmodium vivax
C) Toxoplasma gondii
D) Leishmania tropica

Answer: A) Trypanosoma brucei
Explanation: Sleeping sickness (African trypanosomiasis) is transmitted by the tsetse fly.

Question 80

Which virus causes German measles?

A) Rubella virus
B) Morbillivirus
C) Adenovirus
D) Coxsackie virus

Answer: A) Rubella virus
Explanation: Rubella (German measles) is caused by rubella virus, dangerous in pregnancy due to congenital rubella syndrome.

Question 81

Which bacterium causes food poisoning from reheated rice?

A) Bacillus cereus
B) Clostridium perfringens
C) Staphylococcus aureus
D) Salmonella enteritidis

Answer: A) Bacillus cereus
Explanation: B. cereus spores survive cooking and cause vomiting/diarrhea when rice is improperly stored.

Question 82

Which bacterium causes scarlet fever?

A) Streptococcus pyogenes
B) Staphylococcus aureus
C) Corynebacterium diphtheriae
D) Haemophilus influenzae

Answer: A) Streptococcus pyogenes
Explanation: Scarlet fever is caused by S. pyogenes releasing erythrogenic toxin.

Question 83

Which microorganism causes cholera-like diarrhea in immunocompromised patients?

A) Cryptosporidium parvum
B) Giardia lamblia
C) Entamoeba histolytica
D) Balantidium coli

Answer: A) Cryptosporidium parvum
Explanation: Cryptosporidiosis causes severe watery diarrhea, especially in AIDS patients.

Question 84

Which bacterium is associated with peptic ulcers?

A) Helicobacter pylori
B) Escherichia coli
C) Salmonella typhi
D) Vibrio cholerae

Answer: A) Helicobacter pylori
Explanation: H. pylori colonizes stomach lining and is linked to ulcers and gastric cancer.

Question 85

Which virus causes polio?

A) Enterovirus
B) Rhinovirus
C) Adenovirus
D) Norovirus

Answer: A) Enterovirus
Explanation: Poliovirus, an enterovirus, infects motor neurons causing paralysis.

Question 86

Which microorganism causes cat-scratch disease?

A) Bartonella henselae
B) Pasteurella multocida
C) Francisella tularensis
D) Yersinia pestis

Answer: A) Bartonella henselae
Explanation: Cat-scratch disease is caused by B. henselae, transmitted by cat scratches or bites.

Question 87

Which virus causes smallpox?

A) Variola virus
B) Vaccinia virus
C) Varicella-zoster virus
D) Rubella virus

Answer: A) Variola virus
Explanation: Smallpox was caused by variola virus, eradicated by global vaccination.

Question 88

Which bacterium is responsible for Legionnaires’ disease?

A) Legionella pneumophila
B) Klebsiella pneumoniae
C) Mycoplasma pneumoniae
D) Streptococcus pneumoniae

Answer: A) Legionella pneumophila
Explanation: L. pneumophila spreads via inhalation of contaminated water droplets.

Question 89

Which fungus causes athlete’s foot?

A) Trichophyton rubrum
B) Candida albicans
C) Cryptococcus neoformans
D) Aspergillus niger

Answer: A) Trichophyton rubrum
Explanation: Athlete’s foot (tinea pedis) is caused by dermatophytes like T. rubrum.

Question 90

Which bacterium lacks a cell wall?

A) Mycoplasma pneumoniae
B) Chlamydia trachomatis
C) Rickettsia prowazekii
D) Treponema pallidum

Answer: A) Mycoplasma pneumoniae
Explanation: M. pneumoniae causes atypical pneumonia and is resistant to beta-lactam antibiotics.

Question 91

Which bacterium causes bubonic plague?

A) Yersinia pestis
B) Francisella tularensis
C) Bartonella henselae
D) Pasteurella multocida

Answer: A) Yersinia pestis
Explanation: Plague is transmitted via flea bites carrying Y. pestis.

Question 92

Which virus causes mumps?

A) Paramyxovirus
B) Adenovirus
C) Herpesvirus
D) Poxvirus

Answer: A) Paramyxovirus
Explanation: Mumps virus (paramyxovirus) causes swelling of salivary glands.

Question 93

Which bacterium is responsible for diphtheria?

A) Corynebacterium diphtheriae
B) Bacillus anthracis
C) Clostridium tetani
D) Bordetella pertussis

Answer: A) Corynebacterium diphtheriae
Explanation: C. diphtheriae produces diphtheria toxin, leading to throat pseudomembrane.

Question 94

Which parasite causes malaria?

A) Plasmodium species
B) Toxoplasma gondii
C) Trypanosoma cruzi
D) Leishmania donovani

Answer: A) Plasmodium species
Explanation: Malaria is caused by Plasmodium falciparum, vivax, malariae, and ovale.

Question 95

Which bacterium produces botulinum toxin?

A) Clostridium botulinum
B) Clostridium tetani
C) Bacillus anthracis
D) Pseudomonas aeruginosa

Answer: A) Clostridium botulinum
Explanation: C. botulinum produces neurotoxin blocking acetylcholine, causing paralysis.

Question 96

Which virus causes hepatitis C?

A) Flavivirus
B) Hepadnavirus
C) Picornavirus
D) Retrovirus

Answer: A) Flavivirus
Explanation: Hepatitis C virus belongs to the Flaviviridae family, transmitted via blood.

Question 97

Which bacterium is linked with dental caries?

A) Streptococcus mutans
B) Streptococcus pyogenes
C) Lactobacillus acidophilus
D) Staphylococcus aureus

Answer: A) Streptococcus mutans
Explanation: S. mutans metabolizes sugars into acids, damaging tooth enamel.

Question 98

Which virus causes Ebola?

A) Filovirus
B) Rhabdovirus
C) Retrovirus
D) Adenovirus

Answer: A) Filovirus
Explanation: Ebola virus belongs to Filoviridae, causing hemorrhagic fever with high mortality.

Question 99

Which bacterium causes tuberculosis?

A) Mycobacterium tuberculosis
B) Mycobacterium leprae
C) Nocardia asteroides
D) Bacillus anthracis

Answer: A) Mycobacterium tuberculosis
Explanation: TB is caused by M. tuberculosis, transmitted via airborne droplets.

Question 100

Which virus causes AIDS?

A) HIV
B) Hepatitis B virus
C) Influenza virus
D) Cytomegalovirus

Answer: A) HIV
Explanation: AIDS (Acquired Immunodeficiency Syndrome) is caused by Human Immunodeficiency Virus, a retrovirus.

Mastering microbiology concepts is essential for passing the NCLEX and becoming a safe and effective nurse. The above 50 MCQs with explanations (51–100) provide a strong foundation for your exam preparation.

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