Bacteriology USMLE Step 1 Practice Questions
62 board-style USMLE Step 1 questions in Microbiology/Immunology. Each question shows the correct answer; create a free account for the full explanation and adaptive practice.
- USMLE Step 1 · medium25. A 51-year-old man sustains a deep crush injury to his leg during a farm accident. Two days later, he presents with severe pain, crepitus, and foul-smelling purulent discharge. V…
- USMLE Step 1 · hard26. A 38-year-old man presents with a 3-month history of productive cough, unintentional 8-kg weight loss, and night sweats. Vital signs show BP 118/76, HR 92, RR 18, temp 37.8°C, a…
- USMLE Step 1 · medium27. A 72-year-old man on chemotherapy presents with fever (39.2°C), confusion, and neck stiffness two weeks after consuming unpasteurized cheese. Vital signs show HR 108, BP 136/82,…
- USMLE Step 1 · medium28. A 5-year-old boy presents with fever (39.2°C), abdominal cramping, and small-volume bloody diarrhea after a daycare outbreak. Vital signs show HR 115/min, RR 22/min, BP 100/62 m…
- USMLE Step 1 · easy29. A 34-year-old man returns from South Asia presenting with profuse watery diarrhea, severe dehydration, and abdominal cramping for 3 days. Vital signs show BP 90/60 mmHg, HR 118/…
- USMLE Step 1 · medium30. A 19-year-old woman presents with her third episode of gonococcal cervicitis in 12 months despite appropriate ceftriaxone and azithromycin treatment. Vital signs show BP 118/76,…
- USMLE Step 1 · easy31. A 17-year-old male presents with a painful, fluctuant abscess on his thigh following football practice. Vital signs show BP 118/76, HR 92, RR 16, Temp 38.2°C, SpO2 98% on room a…
- USMLE Step 1 · easy32. A 7-year-old boy presents for routine health maintenance with vital signs BP 110/70 mmHg, HR 88/min, RR 20/min, temperature 37.2°C, and SpO2 98% on room air. He receives a boost…
- USMLE Step 1 · medium33. A 35 year old woman has severe seasonal allergic rhinitis that has not improved with antihistamines or intranasal glucocorticoids. She starts a program of repeated administratio…
- USMLE Step 1 · medium34. A 2-year-old boy with functional asplenia secondary to sickle cell disease (hemoglobin S on electrophoresis) presents for preventive vaccination against encapsulated bacteria. V…
- USMLE Step 1 · easy35. A 6-year-old boy presents with recurrent bacterial sinusitis (HR 102, BP 108/70, RR 22, Temp 38.2°C). CT sinuses shows opacification of maxillary sinuses with normal neutrophil…
- USMLE Step 1 · hard36. A 14 month old boy is evaluated for persistent fever and cervical lymphadenitis 6 weeks after receiving the BCG vaccine outside the United States. Culture of a lymph node aspira…
- USMLE Step 1 · medium37. A 23 year old woman comes to the clinic because of recurrent sinus infections and 3 episodes of bacterial pneumonia over the past 2 years. She has chronic diarrhea and notes tha…
- USMLE Step 1 · hard38. A 30-year-old researcher in a microbiology laboratory adds an antibiotic toxin to isolated mitochondria. Within minutes, ATP production ceases completely, the proton gradient ac…
- USMLE Step 1 · medium39. A 35-year-old healthcare worker with no respiratory symptoms undergoes TB exposure screening. Forty-eight hours after intradermal PPD placement, she develops a 16 mm area of ind…
- USMLE Step 1 · hard40. A 4-week-old laboratory mouse receives an intraperitoneal injection of live nonencapsulated Streptococcus pneumoniae mixed with heat-killed encapsulated strain. Within 48 hours,…
- USMLE Step 1 · medium41. A 68-year-old woman presents with fever (38.9°C), malaise, and knee swelling 10 days after prosthetic knee arthroplasty. Vital signs show HR 102/min, BP 138/88 mmHg, RR 18/min,…
- USMLE Step 1 · medium42. A 24-year-old woman presents to the emergency department with fever (39.2°C), vomiting, and a diffuse erythematous sunburn-like rash. Vital signs show hypotension (88/56 mmHg),…
- USMLE Step 1 · medium43. A 61-year-old woman on mechanical ventilation for 8 days develops fever (38.9°C), tachycardia (HR 112), and purulent sputum. Chest X-ray shows new bilateral infiltrates. Sputum…
- USMLE Step 1 · medium44. A 67-year-old man presents with fever (39.2°C), hypotension (BP 88/52), and confusion. Blood cultures grow gram-negative rods. On examination, he has warm extremities and tachyc…
- USMLE Step 1 · medium45. A 47-year-old male presents with a nonproductive cough and rales on his chest examination. A chest x-ray film suggests atypical pneumonia. The pneumonia resolves after treatment…
- USMLE Step 1 · medium46. A 68-year-old male with alcoholic cirrhosis presents with abdominal distension and hematemesis. Vital signs: BP 92/58, HR 108, RR 20, Temp 38.5°C, SpO2 98% on room air. Paracent…
- USMLE Step 1 · medium47. A culture of Staphylococcus aureus bacteria is selected over many months for its ability to grow in increasing concentrations of penicillin. When colonies of this original cultu…
- USMLE Step 1 · medium48. An 18-year-old, previously healthy female presents to the student health service with fever, vomiting, and diarrhea. On physical examination, she is hypotensive, red, sunburn-li…