USMLE Microbiology Question Base

About a month after being bitten by a bat, a man develops an influenza-like illness. He subsequently develops striking mood changes, pharyngeal spasms with drooling, and seizures, and he falls into a coma. He eventually dies of his illness. This patient’s deterioration was most likely caused by a virus from which of the following groups?

After eating a dinner of leftovers that included rewarmed vegetable fried rice, a 17-year-old boy develops diarrhea and stomach pain. Which of the following is the most likely pathogen?

A 47 year old man presents with a nonproductive cough and rales on his chest examination. A chest x-ray film suggests atypical pneumonia. The pneumonia resolves after the treatment with azithromycin. A diagnosis of psittacosis is established by the presence of complement fixing antibodies against chlamydophila psittaci in the convalescent serum. Which of the following is the most likely occupation of this patient ?

A French exchange student in a town near the Ohio River presents to the local hospital with headache, fever, malaise, and nonproductive cough. He became ill several days after cleaning and moving a chicken coop where hundreds of chickens had roosted for many years. Which of the following microorganisms is most likely responsible for his illness?

Following a barbecue hosted by a hunter who served “bear hamburgers,” several guests develop abdominal pain and diarrhea; their condition progresses about a week later to fever, myalgia, periorbital edema, and petechial hemorrhages in the conjunctiva. A peripheral blood smear shows an increased eosinophil count. Which of the following is the most likely cause of these symptoms?

A young mother takes her infant to the pediatrician for the first time. The pediatrician notices the infant’s teeth are yellow. The antibiotic this mother most likely took during pregnancy

A 35-year-old man presents to the emergency depart­ment with intense back pain. He is hydrated and given pain medication. After several hours, he passes a kidney stone. Laboratory analysis of the stone reveals that it is composed of struvite (magnesium ammonium phos­phate). Infection with which of the following organisms promotes the production of such stones?

A culture of smooth Streptococcus agalactiae bacteria is grown in nutrient broth and allowed to incubate until the culture enters the decline phase of the growth curve. An extract of this process is added to a culture of rough S. agalactiae the logarithmic phase of the growth curve and incubated for 24 hours under appropriate culture conditions. The resulting culture develops some smooth and some rough strains of S. agalactiae. Purified DNase is then added to the flask and the culture is agitated gently lit 2 hours at 37°C. Afterward only rough strains of S. agalactiae are isolated from the culture. Which of the following processes would achieve the production of encapsulated S. agalactiae in this system?

An 18-year-old, previously healthy woman presents to the student health service with fever, vomiting, and diarrhea. On physical examination, she is hypotensive and has an erythematous, red, sunburn-like skin rash. She is currently menstruating and has. been using super-absorbent tampons. Which of the following findings from a positive culture would confirm the suspected diagnosis?

A 5-year-old child who has not had routine pediatric care develops a febrile disease with cough and a blotchy rash, and is brought to the emergency department On physical examination, there is cervical and axillary lymphadenopathy. Also noted is an erythematous, maculopapular rash behind the cars and along the hairline, involving the neck and, to a lesser extent, the trunk. Examination of this patient’s oropharynx would likely reveal which of the following lesions?

A 23-year-old woman suffers from a condition in which her antibodies react with antigens present on the surface of cells. The mechanism of action involves complement fixation by the antibody-antigen complex, which causes lysis or phagocytosis of the affected cell. Which of the following conditions is an example of this type of hypersensitivity?

A 20-year-old man with stridor is brought to the emergency department by his girlfriend. He had been complaining of abdominal pain earlier in the day. Physical examination is significant for well-demarcated regions of subcutaneous edema. He has had similar episodes before, and his mother and sister have the same condition. Which of the following substances is most likely deficient in this patient?

A 68-year-old patient with alcoholic cirrhosis is hospitalized with ascites and esophageal varices. The patient’s temperature is 38.3^oC (101.0^o F). Paracentesis reveals a polymorphonuclear cell count of 300/mm. Which of the following is the most likely infecting organism?

A 3-year-old girl presents with recurrent subcutaneous abscesses and furuncles. She has a history of pneumonia due to Serratia marcescens. Which of the following enzymes is most likely deficient in her neutrophils?

A patient presents with right lower-quadrant pain, fever, and diarrhea. Physical examination reveals diffuse abdominal tenderness; laboratory examination shows a moderate leukocytosis, leading to a presumptive diagnosis of acute appendicitis. Surgical exploration of the abdomen reveals mesenteric adenitis, but the appendix is normal. Which of the following organisms is most likely responsible for these signs and symptoms?

Which of the following cell surface markers is required for lysis of IgG-coated target cells (antibody-dependent, cell-mediated cytotoxicity, or ADCC) by natural killer cells?

A 34-year-old primigravid woman at 32 weeks gestation comes to the emergency department complaining of fever chills, dysuria, and back pain. The symptoms started 6 days ago with burning on urination and have progressively worsened. Her temperature is 39.1^o C. Physical examination shows left costovertebral angle tenderness. Urinalysis is positive for leukocytes and nitrites, Which of the following interleukins is being produced by macrophages and is stimulating fever production by its action on this patient’s hypothalamic cells ??

A baby born at 32 weeks’ gestation with Apgar scores of 2 and 7 was placed in the neonatal intensive care unit. She developed a fever and leukocytosis; lumbar puncture revealed pleocytosis with increased protein, decreased glucose, and grain-positive rods. Which of the following organisms was most likely isolated from the CSF?

A 27-year-old woman conies to the physician because of a 4-week history of lethargy and fatigue. She is gener­ally healthy and, except for a red, annular lesion on her right buttock 4 weeks ago, she has no other complaints. She does not smoke cigarettes and does not drink alco­hol. She proudly says that she goes for an afternoon jog 5 days a week in the woods by her home. Physical examination shows diffuse muscle tenderness and stiff­ness of the joints. Global eradication of this disease is unlikely in the foreseeable future because the causative organism

A 24-year-old woman in her third trimester of preg­nancy presents with urinary frequency and burning for the past few days. She denies fever, nausea, vomiting, or chills. She takes no medications besides prenatal vita­mins and is generally in good health. Physical examina­tion is remarkable for mild suprapubic tenderness, and a urine dipstick is positive for white blood cells, protein, and a small amount of blood. Culture produces greater than 100,000 colonies of gram-negative bacilli. Which of the following attributes of this uropathogenic organ­ism is most strongly associated with its virulence?

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 culture are capable of growth on blood agar containing 400,000 IU penicillin, the colonies are picked from the agar, placed in a nutrient broth, and a lytic phage is added. The bacteria and phage are cocultured until viral maturation is complete. The culture is centrifuged, and the supernatant is added to culture tubes containing clones of penicillin-sensitive S.aureus. After 4 hours of incubation at 37.0^oC, these broth cultures are poured onto blond agar Petri dishes containing 400,000 IU penicillin and incubated for 24 hours Out of 100 Petri dishes, 4 grow colonies. What Process has taken place in this experiment?

A 16-year-old boy with sickle cell disease is hospitalized for a severe infection. His spleen has autosple¬nectomized, and he has had other minor infections in the past. His symptoms include fever, chills, cough, and chest pain. Bacteria from the patient’s sputum are optochin-sensitive organisms with a positive Quellung reaction. Which of the following is the most likely pathogen?

After high-dose chemotherapy and irradiation, a 35-year-old woman with acute myeloid leukemia in remission receives a bone marrow transplant from her HLA-matched brother. One week after the graft, the patient develops a fever and a maculopapular rash over her upper extremities and back. She also notes abdominal pain and diarrhea. Laboratory examination is remarkable for elevation of alkaline phosphatase and bilirubin. Which of the following is the most likely cause of this patient’s symptoms?

A 3-week-old infant is found to have a particular virus. The family practitioner is especially concerned because the virus produces disease or sequelae that is/are more severe if the infection occurs at a very young age. This infant is most likely infected with which of the following viruses?

A 2-year-old boy presents to the emergency department with pneumonia. Since the age of 6 months, he has had recurrent pneumonia and sinusitis due to Streptococcus pneumoneae and Haemophilus influenzae. Careful assessment of his immune function would likely reveal abnormal function of the

A 32-year-old female presents to the office with fever and chills of 2 weeks’ duration. She also noticed blood in her urine this morning. She has a history of recent treatment for Lyme disease while visiting her daughter in upper New York State. Although she finished the course of doxycycline prescribed by her physician, she says she does not feel better. As part of her workup, peripheral blood smear stained with Wright-Giemsa identifies red blood cells. Which of the following is most likely causing her current symptoms?

A 24-year-old woman has fever, malaise, and a dry, nonproductive cough. She also complains of headache, muscle aches, and leg pain. Laboratory values arc signifi­cant for elevated cold agglutinins. Which of the following microorganisms is responsible for her symptoms?

A 3-week-old boy develops focal seizures, lethargy, and vomiting. Examination shows a bulging fontanelle. Which of the following organisms should he suspected?

After passing his physical examination, a 19-year-old army recruit gives urine and blood samples for further testing. Serum analysis yields elevated ALT, HBsAg, anti-HBc, HBeAg, and bilirubin. All other values are normal. What is the hepatitis B status of this recruit?

A 7-month-old child presents with a 4-day history of fever, deepening cough, and dyspnea. A chest x-ray film shows multiple interstitial infiltrates and hyperinflation of the lungs. Multinucleated giant cells with cytoplasmic inclusion bodies are seen when a nasal wash is inoculated into tissue culture. The most appropriate therapy includes administration of which of the following drugs?

A 3-year-old boy presents with a 1-day history of loose stools, fever, abdominal cramping, headache, and myalgia. He has no blood in the stool. A careful history reveals that he has several pet turtles. Which of the fol-lowing is the most likely pathogen?

A 20 year old college student presents to the university health clinic with sore throat, fever, and fatigue. Physical exam is significant for cervical lymphadenopathy and mild hepatomegaly. Heterophile antibody tests are negative. Microscopic examination of fibroblasts would be expected to reveal

A 24-year-old woman with a history of allergic rhinitis is involved in an automobile accident and sustains a splenic laceration. She undergoes abdominal surgery and is then transfused with 4 units of blood of the appropriate ABO and Rh type. As the transfusion progresses, she becomes rapidly hypotensive and develops airway edema, consistent with anaphylaxis. Which of the following pre-existing conditions best accounts for these symptoms?

A 7-year-old boy presents to the pediatrician because his mother noticed a “smoky” color to his urine. On questioning the mother, it is revealed that the child had a sore throat several weeks ago that was left untreated. Physical examination reveals hypertension and mild generalized edema. Urinalysis is significant for red blood cell casts. Which of the following accurately describes the microorganism responsible for this child’s illness?

A 21-year-old man presents with cough, fever, and hemoptysis. Blood tests show significantly elevated BUN and creatinine. Immunofluorescent microscopy reveals a diffuse linear pattern of fluorescence along the basement membranes of. alveolar septa and glomerular capillaries. Which type of hypersensitivity is associated with this disease?

A 20-year-old woman presents with a 2-day history of dysuria and increased urinary frequency. She states that she was recently married and was not sexu¬ally active prior to the marriage. Physical examination reveals a temperature of 100.7°F with normal vital signs. Gynecologic examination reveals no evidence of discharge, vaginitis, or cervicitis. Urinalysis reveals 14 white blood cells per high-powered field with many grant-negative rods. Which of the following is the most appropriate pharrnacotherapy?

A 25-year-old Afghani immigrant presents with a confluent maculopapular rash that began on her face then spread downward over her trunk. She states that 3 days ago she started having a fever and headache, with bilateral pain associated with the front and back of her neck. She also complains of joint pain. Which of the following diseases does she most likely have?

An otherwise healthy patient who has just received a prosthetic aortic valve develops postoperative fever. Blood cultures are done, and she is given broad-spectrum antibiotics. Two days later she is still febrile and clinically deteriorating. Which of the following is the most likely pathogen?

A formula-fed, 1-month-old boy is exposed to his sister, who has chickenpox. He does not develop signs of varicella. His mother had the infection 5 years ago. Which class of immunoglobulins did he acquire from his mother in utero that protected him from this virus?

A 53-year-old engineer with diabetes mellitus comes to the employee health center for an annual examina­tion. She has no complaints at this time. A review of her chart reveals that she is due for a few vaccinations, including the influenza A vaccine. She questions the physician about the necessity of the vaccine because she just received one a year ago. The physician should respond that last year’s influenza vaccine may be ineffective today because influenza A

A 54-year-old man with chronic renal failure receives a kidney transplant and is given immunosuppressive therapy with cyclosporine. Over the next 6 months, the patient’s creatinine levels progressively rise, and a needle biopsy of the kidney is performed. What is the biopsy most likely to show?

A 33-year-old HIV-positive man complains of head­ache and blurred vision. Physical examination revels papilledema and ataxia. Head CT is normal but CSF obtained by lumbar puncture reveals encapsulated organisms’ observable with India ink. Which of the following is true concerning this organism?

A 47-year-old man with a history of sickle cell dis­ease has had numerous hospitalizations requiring the placement of IV lines. The patient has poor peripheral venous access, and a catheter is placed in right sub­clavian vein. The patient subsequently develops right arm discomfort and swelling and a temperature of 40.1^o C with chills. Multiple blood cultures are taken, and gram-positive cocci are isolated. The organism is catalase-positive and produces whitish colonies on mannitol salt agar. The colonies are gamma-hemolytic on sheep blood agar. Which of the following organisms is the most likely cause of this patient’s symptoms?

A 65-year-old man undergoes coronary artery bypass surgery that entails grafting the left internal mammary artery to the left main coronary artery to form an alter¬native conduit for blood flow. This patient received a(n)

A 23-year-old woman with a history of sickle cell disease presents with fever and severe bone pain localized to her left tibia. An x-ray film reveals a lytic lesion, and blood cultures reveal infection. A bone culture grows gram-negative rods. Which of the following best describes the infecting organism?

A 69-year-old alcoholic man comes to the emergency department because of high fever, chills, and a cough. He says that he has been producing “lots of thick, bloody, gelatinous mucus” over the past 2 days. Gram staining of the sputum reveals pinkish-red bacilli. Chest x-ray shows consolidation of the upper lobes. Which of the following is found only in microorganisms with this color Gram staining?

A 60-year-old woman comes to the physician because of fever, chills, and a cough for the past 2 weeks. She lives at home with her husband, has no chronic medical conditions, and has not traveled recently. She does not smoke cigarettes or drink alcohol Her temperature is 38.2°C (100.8^oF). Physical examination reveals altered breath sounds. Chest x-ray is abnormal. Which of the following is the most likely causal organism?

A 58-year-old alcoholic man with multiple dental caries develops a pulmonary abscess and is treated with anti­biotics. Several days later, he develops nausea, vomiting, abdominal pain, and voluminous, malodorous, green diarrhea. Which of the following antibiotics is most likely responsible for this patient’s symptoms?

A 4-year-old child who has had repeated infections with staphylococci and streptococci has normal phagocytic function and delayed hypersensitivity responses. Lymph node biopsy would most likely reveal