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NBME-style Microbiology Practice Exam Questions and correct answers 2025 . Questions are r, Exams of Microbiology

Texas CollegeMicrobiology

NBME-style Microbiology Practice Exam Questions and correct answers 2025 . Questions are representative of USMLE Step 1/ NBME-style multiple-choice format.

Typology: Exams

2024/2025

Available from 06/23/2025

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NBME-style Microbiology Practice Exam
Questions and correct answers 2025
. Questions are representative of USMLE Step 1/ NBME-style multiple-choice format.
1. A 5-year-old boy develops a sore throat and fever. His throat is
erythematous with grayish-white exudates. Throat culture grows beta-
hemolytic colonies that are bacitracin-sensitive. Which is the most likely
pathogen?
• Streptococcus agalactiae
• Streptococcus mutans
• Streptococcus pyogenes
• Streptococcus pneumoniae
• Corynebacterium diphtheriae
Streptococcus pyogenes is Group A Streptococcus, which is bacitracin-sensitive and
commonly causes pharyngitis with exudate.
2. A patient who recently returned from Africa presents with cyclic fevers,
chills, and malaise. Blood smear shows trophozoites in RBCs. Which of the
following is the most likely organism?
• Babesia microti
• Plasmodium falciparum
• Trypanosoma brucei
• Leishmania donovani
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff
pf12
pf13
pf14
pf15
pf16
pf17
pf18
pf19
pf1a
pf1b
pf1c
pf1d
pf1e
pf1f
pf20
pf21
pf22
pf23
pf24
pf25
pf26
pf27

Partial preview of the text

Download NBME-style Microbiology Practice Exam Questions and correct answers 2025 . Questions are r and more Exams Microbiology in PDF only on Docsity!

NBME-style Microbiology Practice Exam

Questions and correct answers 2025

. Questions are representative of USMLE Step 1/ NBME-style multiple-choice format.

  1. A 5-year-old boy develops a sore throat and fever. His throat is erythematous with grayish-white exudates. Throat culture grows beta- hemolytic colonies that are bacitracin-sensitive. Which is the most likely pathogen?
  • Streptococcus agalactiae
  • Streptococcus mutans
  • Streptococcus pyogenes
  • Streptococcus pneumoniae
  • Corynebacterium diphtheriae Streptococcus pyogenes is Group A Streptococcus, which is bacitracin-sensitive and commonly causes pharyngitis with exudate.
  1. A patient who recently returned from Africa presents with cyclic fevers, chills, and malaise. Blood smear shows trophozoites in RBCs. Which of the following is the most likely organism?
  • Babesia microti
  • Plasmodium falciparum
  • Trypanosoma brucei
  • Leishmania donovani
  • Toxoplasma gondii Plasmodium falciparum causes malaria with cyclic fevers and trophozoites visible inside RBCs.
  1. A 24-year-old sexually active woman presents with dysuria and mucopurulent cervical discharge. Which organism is most likely responsible?
  • Gardnerella vaginalis
  • Neisseria gonorrhoeae
  • Trichomonas vaginalis
  • Chlamydia trachomatis
  • Mycoplasma genitalium Neisseria gonorrhoeae commonly causes cervicitis with purulent discharge and dysuria in women.
  1. A 3-year-old develops diarrhea after a trip to a petting zoo. Stool culture on sorbitol-MacConkey agar shows colorless colonies. Which toxin is involved?
  • LT toxin
  • ST toxin
  • Shiga-like toxin
  • Cholera toxin
  • Alpha-toxin EHEC (e.g., O157:H7) produces Shiga-like toxin and doesn't ferment sorbitol, explaining the colorless colonies.
  • Lethal toxin
  • Shiga toxin
  • Lipid A endotoxin Scarlet fever caused by S. pyogenes involves erythrogenic exotoxin, a superantigen.
  1. Which bacterium is associated with pseudomembranous colitis following antibiotic use?
  • Escherichia coli
  • Bacteroides fragilis
  • Clostridioides difficile
  • Clostridium perfringens
  • Proteus mirabilis C. difficile overgrowth after antibiotics produces toxins A and B, leading to pseudomembranous colitis.
  1. A man is bitten by a dog and develops cellulitis within 24 hours. Which is the most likely organism?
  • Staphylococcus aureus
  • Pasteurella multocida
  • Bartonella henselae
  • Capnocytophaga canimorsus
  • Streptococcus viridans Pasteurella multocida, found in dog and cat mouths, causes rapid-onset soft tissue infections.
  1. A woman with AIDS presents with chronic watery diarrhea. Stool acid-fast staining reveals oocysts. What is the organism?
  • Giardia lamblia
  • Entamoeba histolytica
  • Cryptosporidium parvum
  • Cyclospora cayetanensis
  • Isospora belli Cryptosporidium is an acid-fast oocyst-forming protozoan causing chronic diarrhea in immunocompromised patients. (More questions continued below...) NBME Microbiology Practice Exam (continued)
  1. A neonate develops meningitis. Culture shows gram-negative rods. Which is most likely?
  • Staphylococcus epidermidis
  • Streptococcus pneumoniae
  • Listeria monocytogenes
  • Escherichia coli
  • Neisseria meningitidis E. coli (especially K1 strain) is a common cause of neonatal meningitis along with Group B strep and Listeria.
  • Mycoplasma pneumoniae Klebsiella causes necrotizing pneumonia with thick, bloody (currant jelly) sputum.
  1. A teenage boy has fever, sore throat, posterior cervical lymphadenopathy, and atypical lymphocytosis. What virus is likely?
  • Cytomegalovirus
  • HSV- 1
  • Epstein-Barr virus
  • Adenovirus
  • HIV EBV causes mononucleosis with atypical lymphocytes and posterior cervical lymphadenopathy.
  1. Which fungal pathogen is most likely to cause meningitis in AIDS patients and is detected with India ink?
  • Candida albicans
  • Cryptococcus neoformans
  • Aspergillus fumigatus
  • Histoplasma capsulatum
  • Coccidioides immitis Cryptococcus causes meningitis in immunocompromised hosts and appears as encapsulated yeast in India ink stain.
  1. Which virus causes congenital sensorineural hearing loss, periventricular calcifications, and hepatosplenomegaly?
  • Rubella virus
  • Cytomegalovirus
  • Herpes simplex virus
  • Toxoplasma gondii
  • Varicella-zoster virus Congenital CMV is the most common cause of congenital viral infection and leads to sensorineural hearing loss.
  1. A person develops watery diarrhea after drinking untreated mountain stream water. Trophozoites with two nuclei are seen. What is the pathogen?
  • Entamoeba histolytica
  • Giardia lamblia
  • Cryptosporidium parvum
  • Cyclospora cayetanensis
  • Trichuris trichiura Giardia is transmitted through freshwater; trophozoites have a characteristic “face-like” appearance.
  1. Which virus can cause progressive multifocal leukoencephalopathy in immunosuppressed patients?
  • HSV- 2
  • CMV
  • JC virus

Haemophilus ducreyi causes chancroid, a painful ulcer with tender lymphadenopathy ("you do cry").

  1. A patient with a prosthetic heart valve presents with fever and new murmur. Blood cultures show gram-positive cocci in clusters. Which organism is likely?
  • Streptococcus viridans
  • Enterococcus faecalis
  • Staphylococcus epidermidis
  • Staphylococcus aureus
  • Streptococcus pyogenes Staphylococcus epidermidis is a common cause of prosthetic valve endocarditis due to its biofilm formation.
  1. A farmer presents with a painless black eschar on his hand. Which organism is responsible?
  • Clostridium perfringens
  • Bacillus anthracis
  • Sporothrix schenckii
  • Mycobacterium marinum
  • Francisella tularensis Bacillus anthracis causes cutaneous anthrax with a painless black eschar due to lethal factor.
  1. Which parasite causes perianal itching, especially at night, and is diagnosed via the "scotch tape" test?
  • Ascaris lumbricoides
  • Enterobius vermicularis
  • Trichuris trichiura
  • Strongyloides stercoralis
  • Taenia solium Enterobius (pinworm) causes nocturnal perianal pruritus and is diagnosed with tape test.
  1. A woman develops vaginal itching and frothy green discharge. A wet mount shows motile protozoa. What is the organism?
  • Gardnerella vaginalis
  • Candida albicans
  • Trichomonas vaginalis
  • Neisseria gonorrhoeae
  • Chlamydia trachomatis Trichomonas is a flagellated protozoan causing green discharge and vaginal inflammation.
  1. A boy with cat exposure develops fever and swollen lymph nodes. Which organism is likely?
  • Brucella spp.
  • Yersinia pestis
  • Bartonella henselae
  • Pasteurella multocida
  • Francisella tularensis
  • Blastomyces dermatitidis
  • Paracoccidioides brasiliensis
  • Cryptococcus neoformans Blastomyces is endemic to the Great Lakes and causes pulmonary and skin infections.
  1. What is the most likely cause of pneumonia in a college student with non- productive cough and normal WBC count?
  • Streptococcus pneumoniae
  • Klebsiella pneumoniae
  • Haemophilus influenzae
  • Mycoplasma pneumoniae
  • Legionella pneumophila Mycoplasma causes "walking pneumonia" in young adults; chest x-ray often looks worse than symptoms.
  1. Which parasite causes liver abscesses and flask-shaped ulcers in the colon?
  • Giardia lamblia
  • Entamoeba histolytica
  • Cryptosporidium parvum
  • Schistosoma mansoni
  • Toxoplasma gondii Entamoeba invades the colonic wall and can form liver abscesses with anchovy paste-like contents.
  1. A patient who eats undercooked pork develops seizures due to brain cysts. What organism is responsible?
  • Trichinella spiralis
  • Toxoplasma gondii
  • Taenia solium
  • Echinococcus granulosus
  • Ascaris lumbricoides Taenia solium causes neurocysticercosis, leading to seizures and calcified brain cysts.
  1. A child with a rash on face that spreads and becomes vesicular is found to have a honey-colored crust. What is the most likely cause?
  • Staphylococcus aureus
  • Streptococcus pyogenes
  • Varicella-zoster virus
  • Coxsackievirus
  • Herpes simplex virus S. aureus is a common cause of non-bullous impetigo with honey-colored crusts.
  1. What is the mechanism of diphtheria toxin?
  • ADP-ribosylation of G protein
  • Activation of adenylate cyclase
  • Inhibition of EF- 2
  • Inhibition of DNA synthesis
  • Cleavage of SNARE proteins
  • Aspergillus fumigatus
  • Histoplasma capsulatum
  • Coccidioides immitis Candida forms pseudohyphae and is a common cause of catheter-related fungemia.
  1. Which organism is transmitted via tick bite and causes fever, hemolytic anemia, and "Maltese cross" forms on smear?
  • Babesia microti
  • Plasmodium vivax
  • Rickettsia rickettsii
  • Borrelia burgdorferi
  • Anaplasma phagocytophilum Babesia causes a malaria-like illness and shows Maltese cross inside RBCs.
  1. A patient presents with oral thrush, esophagitis, and diaper rash. Which fungus is the cause?
  • Cryptococcus neoformans
  • Candida albicans
  • Aspergillus fumigatus
  • Mucor species
  • Histoplasma capsulatum Candida albicans causes mucocutaneous infections and is common in immunocompromised hosts.
  1. A man has non-painful genital papules that ulcerate and heal. Later, he develops gummas and tabes dorsalis. What stage of syphilis is he in now?
  • Primary
  • Secondary
  • Tertiary
  • Latent
  • Congenital Tertiary syphilis includes gummas, neurosyphilis (tabes dorsalis), and cardiovascular complications.
  1. Which bacterium uses actin rockets to move from cell to cell and causes meningitis in the elderly?
  • Neisseria meningitidis
  • Listeria monocytogenes
  • Streptococcus pneumoniae
  • Escherichia coli
  • Salmonella enterica Listeria spreads intracellularly using actin polymerization and causes meningitis in neonates and elderly.
  1. Which virus causes a descending maculopapular rash starting at the hairline, Koplik spots, and cough?
  • Rubella virus
  • Parvovirus B
  1. What is the most common cause of viral gastroenteritis in adults in the US?
  • Adenovirus
  • Rotavirus
  • Astrovirus
  • Norovirus
  • Coronavirus Norovirus is a common cause of viral gastroenteritis, especially in cruise ships and adults.
  1. A pigeon breeder presents with headache, fever, and stiff neck. CSF shows yeast with a thick capsule. What is the cause?
  • Candida albicans
  • Aspergillus fumigatus
  • Cryptococcus neoformans
  • Histoplasma capsulatum
  • Blastomyces dermatitidis Cryptococcus from bird droppings causes meningitis in immunocompromised patients.
  1. Which virus is transmitted by the Aedes mosquito and causes joint pain, rash, and fever?
  • Dengue virus
  • Chikungunya virus
  • Zika virus
  • West Nile virus
  • Yellow fever virus

Chikungunya causes fever and polyarthritis; spread by Aedes mosquitoes.

  1. A patient presents with rice-water stools. What is the virulence mechanism of the organism responsible?
  • AB toxin that inhibits protein synthesis
  • Invasion of intestinal mucosa
  • Activation of adenylate cyclase via Gs
  • Heat-stable enterotoxin
  • Endotoxin release Vibrio cholerae toxin permanently activates Gs, increasing cAMP and leading to watery diarrhea.
  1. A person in Arizona develops pneumonia and skin nodules. Sputum shows spherules with endospores. Diagnosis?
  • Blastomycosis
  • Histoplasmosis
  • Coccidioidomycosis
  • Cryptococcosis
  • Aspergillosis Coccidioides immitis causes “Valley fever” with spherules containing endospores.
  1. Which bacterial toxin causes flaccid paralysis by inhibiting acetylcholine release?
  • Botulinum toxin
  • Tetanospasmin