Microbiology is one of the most critical areas tested in the NCLEX exam. Understanding bacteria, viruses, infection control, and immune responses is essential for safe nursing practice. To help you prepare effectively, we have compiled NCLEX-style Microbiology MCQs with answers and explanations.

This is Part 1 (Questions 1–50), designed to strengthen your knowledge of pathogens, antibiotics, infection prevention, and laboratory techniques. Each question is carefully selected to match the NCLEX exam pattern and will help you master microbiology concepts step by step.

NCLEX Microbiology MCQs (Part 1: 1–50)

Question 1

Which of the following structures allows bacteria to attach firmly to host surfaces?

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

Answer: C) Pili (Fimbriae)
Explanation: Pili or fimbriae are hair-like structures on bacterial surfaces that help in adhesion to host tissues, a crucial step in infection.

Question 2

Which bacterial shape describes organisms that are spherical?

A) Bacilli
B) Spirilla
C) Cocci
D) Vibrio

Answer: C) Cocci
Explanation: Cocci are spherical-shaped bacteria. Bacilli are rod-shaped, spirilla are spiral-shaped, and vibrio are comma-shaped.

Question 3

The Gram stain differentiates bacteria based on:

A) DNA content
B) Cell wall structure
C) Capsule thickness
D) Presence of pili

Answer: B) Cell wall structure
Explanation: Gram-positive bacteria have thick peptidoglycan layers that retain crystal violet dye, while Gram-negative bacteria have thin walls and an outer membrane.

Question 4

Which of the following is the main function of bacterial endospores?

A) Reproduction
B) Protein synthesis
C) Survival under harsh conditions
D) Energy storage

Answer: C) Survival under harsh conditions
Explanation: Endospores protect bacteria from heat, radiation, chemicals, and desiccation, allowing survival in extreme environments.

Question 5

Which of the following is an obligate intracellular parasite?

A) Bacteria
B) Virus
C) Protozoa
D) Fungi

Answer: B) Virus
Explanation: Viruses cannot reproduce independently and require a living host cell to replicate.

Question 6

The Ziehl-Neelsen stain is used to detect:

A) Fungal spores
B) Acid-fast bacteria
C) Capsules
D) Gram-negative rods

Answer: B) Acid-fast bacteria
Explanation: Mycobacterium species (like M. tuberculosis) retain the red carbol fuchsin dye even after acid-alcohol treatment.

Question 7

Which of the following viruses is associated with cervical cancer?

A) Hepatitis B Virus (HBV)
B) Human Papillomavirus (HPV)
C) Epstein-Barr Virus (EBV)
D) HIV

Answer: B) Human Papillomavirus (HPV)
Explanation: High-risk HPV strains (16 and 18) are linked to cervical and other genital cancers.

Question 8

Which bacterial genus is commonly used in yogurt production?

A) Bacillus
B) Lactobacillus
C) Pseudomonas
D) Clostridium

Answer: B) Lactobacillus
Explanation: Lactobacillus ferments milk sugars into lactic acid, giving yogurt its sour taste and texture.

Question 9

Which of the following is an example of a vector-borne disease?

A) Tuberculosis
B) Malaria
C) Tetanus
D) Cholera

Answer: B) Malaria
Explanation: Malaria is transmitted by the bite of infected Anopheles mosquitoes, making it vector-borne.

Question 10

Which organelle in eukaryotic cells is most similar in function to bacterial plasma membranes?

A) Mitochondria
B) Golgi apparatus
C) Ribosomes
D) Lysosomes

Answer: A) Mitochondria
Explanation: Mitochondria produce energy (ATP) in eukaryotic cells and evolved from bacteria through endosymbiosis.

Question 11

The causative agent of tuberculosis is:

A) Mycobacterium leprae
B) Mycobacterium tuberculosis
C) Corynebacterium diphtheriae
D) Bacillus anthracis

Answer: B) Mycobacterium tuberculosis
Explanation: TB is caused by Mycobacterium tuberculosis, which is acid-fast and spread via airborne droplets.

Question 12

Which of the following diseases is caused by a prion?

A) Creutzfeldt-Jakob disease
B) Influenza
C) Malaria
D) Syphilis

Answer: A) Creutzfeldt-Jakob disease
Explanation: Prions are infectious proteins that cause neurodegenerative diseases such as CJD and mad cow disease.

Question 13

Which of the following structures is found only in Gram-negative bacteria?

A) Teichoic acid
B) Outer membrane
C) Thick peptidoglycan
D) Capsule

Answer: B) Outer membrane
Explanation: Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS), which contributes to toxicity.

Question 14

HIV primarily infects which type of cell?

A) B lymphocytes
B) CD4+ T lymphocytes
C) Red blood cells
D) Neutrophils

Answer: B) CD4+ T lymphocytes
Explanation: HIV targets CD4+ helper T cells, weakening the immune system and leading to AIDS.

Question 15

Which fungus is responsible for causing thrush?

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

Answer: B) Candida albicans
Explanation: Oral thrush and vaginal yeast infections are caused by the overgrowth of Candida albicans.

Question 16

Which bacterial structure provides resistance to phagocytosis?

A) Ribosome
B) Capsule
C) Pili
D) Flagella

Answer: B) Capsule
Explanation: Capsules are protective layers that shield bacteria from being engulfed by immune cells.

Question 17

Which of the following diseases is caused by Clostridium tetani?

A) Botulism
B) Tetanus
C) Gas gangrene
D) Diphtheria

Answer: B) Tetanus
Explanation: Clostridium tetani produces a neurotoxin causing painful muscle spasms known as lockjaw.

Question 18

Which bacterial structure is used for motility?

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

Answer: B) Flagella
Explanation: Flagella are whip-like structures that allow bacterial movement.

Question 19

Which staining technique is used to identify fungal organisms?

A) Acid-fast stain
B) Gram stain
C) KOH preparation
D) Negative stain

Answer: C) KOH preparation
Explanation: Potassium hydroxide dissolves host cells and debris, leaving fungal elements visible.

Question 20

Which of the following is an example of an opportunistic infection in AIDS patients?

A) Streptococcal pharyngitis
B) Pneumocystis pneumonia
C) Common cold
D) Malaria

Answer: B) Pneumocystis pneumonia
Explanation: Pneumocystis jirovecii commonly causes pneumonia in immunocompromised individuals.

Question 21

Which toxin is produced by Vibrio cholerae?

A) Neurotoxin
B) Enterotoxin
C) Exotoxin A
D) Cytotoxin

Answer: B) Enterotoxin
Explanation: Cholera toxin is an enterotoxin that causes severe watery diarrhea.

Question 22

The vector for Lyme disease is:

A) Mosquito
B) Tick
C) Flea
D) Louse

Answer: B) Tick
Explanation: Lyme disease is caused by Borrelia burgdorferi and transmitted by Ixodes ticks.

Question 23

Which organelle is absent in prokaryotic cells?

A) Ribosomes
B) Cell wall
C) Mitochondria
D) Plasma membrane

Answer: C) Mitochondria
Explanation: Prokaryotes lack membrane-bound organelles, including mitochondria.

Question 24

Which of the following is a DNA virus?

A) Influenza virus
B) Rabies virus
C) Adenovirus
D) Measles virus

Answer: C) Adenovirus
Explanation: Adenoviruses are double-stranded DNA viruses that cause respiratory and eye infections.

Question 25

Which bacterial genus produces antibiotics such as streptomycin?

A) Bacillus
B) Streptomyces
C) Clostridium
D) Staphylococcus

Answer: B) Streptomyces
Explanation: Streptomyces are soil-dwelling bacteria that produce many antibiotics.

Question 26

Which type of immunity is provided by vaccines?

A) Natural passive immunity
B) Artificial active immunity
C) Artificial passive immunity
D) Natural active immunity

Answer: B) Artificial active immunity
Explanation: Vaccines stimulate the immune system to produce long-lasting antibodies.

Question 27

Which bacteria cause syphilis?

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

Answer: B) Treponema pallidum
Explanation: Syphilis is a sexually transmitted infection caused by the spirochete Treponema pallidum.

Question 28

Which bacterial infection is commonly associated with undercooked poultry?

A) Salmonella
B) Vibrio
C) E. coli O157:H7
D) Shigella

Answer: A) Salmonella
Explanation: Salmonella species are often transmitted through contaminated poultry and eggs.

Question 29

Which microorganism is responsible for malaria?

A) Virus
B) Bacteria
C) Protozoa
D) Fungus

Answer: C) Protozoa
Explanation: Malaria is caused by Plasmodium species, a protozoan parasite.

Question 30

Which of the following is a dimorphic fungus?

A) Candida albicans
B) Histoplasma capsulatum
C) Aspergillus
D) Penicillium

Answer: B) Histoplasma capsulatum
Explanation: Dimorphic fungi exist as molds at room temperature and yeast at body temperature.

Question 31

Which bacterium causes whooping cough?

A) Bordetella pertussis
B) Corynebacterium diphtheriae
C) Streptococcus pyogenes
D) Haemophilus influenzae

Answer: A) Bordetella pertussis
Explanation: Pertussis (whooping cough) is caused by Bordetella pertussis.

Question 32

Which is the most common cause of urinary tract infections (UTIs)?

A) Staphylococcus aureus
B) Pseudomonas aeruginosa
C) Escherichia coli
D) Klebsiella pneumoniae

Answer: C) Escherichia coli
Explanation: E. coli accounts for the majority of UTIs due to its uropathogenic strains.

Question 33

The causative agent of plague is:

A) Yersinia pestis
B) Salmonella typhi
C) Vibrio cholerae
D) Francisella tularensis

Answer: A) Yersinia pestis
Explanation: Plague (Black Death) is caused by Yersinia pestis, transmitted via fleas.

Question 34

Which bacteria are arranged in grape-like clusters?

A) Streptococcus
B) Staphylococcus
C) Bacillus
D) Vibrio

Answer: B) Staphylococcus
Explanation: Staphylococcus species form clusters resembling grapes.

Question 35

Which parasite causes sleeping sickness?

A) Leishmania donovani
B) Trypanosoma brucei
C) Entamoeba histolytica
D) Giardia lamblia

Answer: B) Trypanosoma brucei
Explanation: African sleeping sickness is transmitted by the tsetse fly.

Question 36

Which type of hypersensitivity reaction is anaphylaxis?

A) Type I
B) Type II
C) Type III
D) Type IV

Answer: A) Type I
Explanation: Type I hypersensitivity involves IgE-mediated allergic reactions such as anaphylaxis.

Question 37

Which bacterial enzyme breaks down hydrogen peroxide?

A) Coagulase
B) Catalase
C) Hyaluronidase
D) Oxidase

Answer: B) Catalase
Explanation: Catalase converts hydrogen peroxide into water and oxygen.

Question 38

Which disease is caused by Epstein-Barr virus (EBV)?

A) Hepatitis
B) Infectious mononucleosis
C) Smallpox
D) Poliomyelitis

Answer: B) Infectious mononucleosis
Explanation: EBV causes mononucleosis, also known as the “kissing disease.”

Question 39

Which parasite causes amebic dysentery?

A) Giardia lamblia
B) Entamoeba histolytica
C) Balantidium coli
D) Trichomonas vaginalis

Answer: B) Entamoeba histolytica
Explanation: Amebic dysentery is caused by E. histolytica.

Question 40

Which microorganism is used in the production of penicillin?

A) Aspergillus
B) Candida
C) Penicillium notatum
D) Rhizopus

Answer: C) Penicillium notatum
Explanation: The antibiotic penicillin was first discovered from Penicillium notatum.

Question 41

Which bacterial toxin is responsible for botulism?

A) Tetanospasmin
B) Botulinum toxin
C) Shiga toxin
D) Cholera toxin

Answer: B) Botulinum toxin
Explanation: Clostridium botulinum produces a neurotoxin that causes flaccid paralysis.

Question 42

Which part of the bacterial cell is targeted by penicillin?

A) Ribosomes
B) Cell wall synthesis
C) Plasma membrane
D) DNA replication

Answer: B) Cell wall synthesis
Explanation: Penicillin inhibits peptidoglycan synthesis in bacterial cell walls.

Question 43

Which virus causes chickenpox?

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

Answer: B) Varicella-zoster virus
Explanation: Chickenpox and shingles are caused by VZV.

Question 44

Which bacteria cause diphtheria?

A) Corynebacterium diphtheriae
B) Streptococcus pyogenes
C) Bacillus anthracis
D) Bordetella pertussis

Answer: A) Corynebacterium diphtheriae
Explanation: Diphtheria is caused by toxin-producing C. diphtheriae.

Question 45

Which microorganism causes leprosy?

A) Mycobacterium tuberculosis
B) Mycobacterium leprae
C) Treponema pallidum
D) Borrelia burgdorferi

Answer: B) Mycobacterium leprae
Explanation: Leprosy (Hansen’s disease) is caused by M. leprae.

Question 46

Which parasite causes giardiasis?

A) Trichomonas vaginalis
B) Giardia lamblia
C) Entamoeba coli
D) Leishmania

Answer: B) Giardia lamblia
Explanation: Giardiasis is an intestinal infection transmitted through contaminated water.

Question 47

Which test differentiates Staphylococcus aureus from other staphylococci?

A) Catalase test
B) Coagulase test
C) Oxidase test
D) Urease test

Answer: B) Coagulase test
Explanation: S. aureus is coagulase-positive, distinguishing it from other staphylococci.

Question 48

Which bacteria cause anthrax?

A) Clostridium perfringens
B) Bacillus anthracis
C) Salmonella typhi
D) Pseudomonas aeruginosa

Answer: B) Bacillus anthracis
Explanation: Bacillus anthracis is the causative agent of anthrax.

Question 49

Which microorganism is known as the “kissing bug” vector?

A) Anopheles mosquito
B) Triatomine bug
C) Tsetse fly
D) Sandfly

Answer: B) Triatomine bug
Explanation: The triatomine bug transmits Trypanosoma cruzi, causing Chagas disease.

Question 50

Which bacterium is associated with peptic ulcer disease?

A) Helicobacter pylori
B) E. coli
C) Salmonella enterica
D) Shigella dysenteriae

Answer: A) Helicobacter pylori
Explanation: H. pylori infects the stomach lining, leading to gastritis and peptic ulcers.

You’ve just completed NCLEX Microbiology MCQs Part 1 (1–50). These questions covered the basics of microbiology, infectious diseases, and laboratory methods. Keep practicing with the next parts for full coverage: