USMLE Microbiology Part 1
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- 1.One of three blood culture bottles drawn from a patient with unexplained fevers reveals gram-positive cocci growing in clusters. Which of the following tests would be most useful in determining whether this organism is a part of the normal skin flora?
- A.
Bacitracin resistance
- B.
Catalase
- C.
Coagulase
- D.
Novobiocin resistance
- E.
Optochin resistance
- 2.A 4-month-old infant presents with failure to thrive, progressive muscular weakness, and poor head control. On questioning, the mother states that she typically feeds the baby soy-based formula sweetened with honey. Which of the following organisms is most likely to be responsible for the child's presentation?
- A.
Clostridium botulinum
- B.
Clostridium difficile
- C.
Clostridium perfringens
- D.
Clostridium tetani
- E.
Corynebacterium diphtheriae
- 3.A 35-year-old woman presents to her gynecologist with complaints of burning on urination for the past 2 days. Dipstick test of her urine demonstrates marked positivity for leukocyte esterase, but no reactivity for nitrite. Urine culture later grows out large numbers of organisms. Which of the following bacteria are most likely to be responsible for this patient's infection?
- A.
Enterobacter sp.
- B.
Enterococcus faecalis
- C.
Escherichia coli
- D.
Klebsiella pneumoniae
- E.
Pseudomonas aeruginosa
- 4.A 37-year-old woman presents with 3 days of progressive joint pain in her ankles, knees, and wrists. She recalls three similar episodes over the past several years. On examination, she has a temperature of 38.7 C, her blood pressure is 110/70 mm Hg, and her heart rate is 90/min. She has a diffuse petechial rash over her trunk and extensor surfaces. Her ankles and knees are swollen, red, and tender with decreased range of motion, and there is tenderness over the tendon sheaths of her hands and forearms. Blood cultures are negative. Aspiration of joint fluid reveals a white cell count of 22,000/mm3 with no visible organisms, but culture on chocolate agar is positive. Which of the following is an attribute of the causative organism that allows it to produce recurrent infections?
- A.
It is an intracellular pathogen
- B.
It is resistant to ceftriaxone
- C.
It is resistant to complement-mediated lysis
- D.
Its capsule is not immunogenic
- E.
Its pili undergo antigenic and phase variation
- 5.A Pap smear from a woman with chronic cervicitis shows cytoplasmic inclusions within epithelial cells. Fluorescent antibodies identify both these inclusions and "elementary bodies." The intracellular organisms causing the infection are unusual because they cannot synthesize which of the following?
- A.
ATP
- B.
Cholesterol
- C.
DNA
- D.
Proteins
- E.
RNA
- 6.A patient with colorectal cancer develops septicemia complicated by endocarditis. You would expect the blood cultures to grow
- A.
Streptococcus agalactiae
- B.
Streptococcus bovis
- C.
Streptococcus pneumoniae
- D.
Streptococcus pyogenes
- E.
Streptococcus viridans
- 7.A 54-year-old woman suffering from influenza deteriorates and develops shaking chills and a high fever. Physical examination is remarkable for dullness to percussion at the left base and decreased breath sounds on the left. Chest x-ray confirms the diagnosis of lobar pneumonia, presumed to be caused by Streptococcus pneumoniae. The patient has no known drug allergies. Which of the following antibiotics would be most appropriate to treat the patient's condition?
- A.
Cefotaxime
- B.
Chloramphenicol
- C.
Erythromycin
- D.
Penicillin
- E.
Vancomycin
- 8.An otherwise healthy 3-year-old child is brought to the pediatrician with umbilicated, flesh-colored papules on his trunk. This condition is related to infection with which of the following viruses?
- A.
Cytomegalovirus
- B.
Herpesvirus 6
- C.
Parvovirus
- D.
Poxvirus
- E.
Variola
- 9.A 39-year-old black man presents with complaints of anorexia, malaise, fatigue, dark urine, and upper abdominal discomfort. He admits to homosexuality, but denies blood transfusions, alcohol intake, or intravenous drug abuse. On physical examination, the patient has a temperature of 100.2 degrees F, scleral icterus, and jaundice. His liver is palpable below the right costal margin, and there is moderate right upper quadrant tenderness. Liver function test results are as follows: total bilirubin 12.4%, SGOT 980 units, SGPT 1200 units. Serologic findings are as follows: anti-hepatitis A IgM negative, HBsAg positive, anti-HBc IgM positive, HBeAg positive, anti-HBsAb negative, hepatitis C negative. When this patient enters the window period, what would likely be the first change in his serologic findings?
- A.
He will become HBcAg positive
- B.
He will become HBc IgG positive
- C.
He will become HBeAg negative
- D.
He will become HBsAb positive
- E.
He will become HBsAg negative
- 10.A 15-year-old girl in a rural community has swollen, painful lymph nodes in her right axilla. Physical examination reveals multiple scratches on her right arm with a papule associated with one of the scratch marks. She states that the scratches occurred about 5 days ago. What type of animal is the most likely source of the infection?
- A.
Cat or kitten
- B.
Chicken
- C.
Dog or puppy
- D.
Horse
- E.
Parrot
- 11.A 73-year-old woman with a history of diabetes presents with left ear pain and drainage of pus from the ear canal. She has swelling and tenderness over the left mastoid bone. Which of the following microorganisms is the most likely causative agent?
- A.
Hemophilus influenzae
- B.
Klebsiella pneumoniae
- C.
Mucor sp
- D.
Pseudomonas aeruginosa
- E.
Streptococcus pyogenes
- 12.A 29-year-old female diagnosed with AIDS has been suffering from a progressive blurring of vision in her right eye. On funduscopic examination, a small white opaque lesion is noted on the retina of her right eye. Which of the following is the most appropriate therapy for this patient?
- A.
Acyclovir
- B.
Amantadine
- C.
Flucytosine
- D.
Ganciclovir
- E.
Zidovudine
- 13.A newborn is infected in utero with an enveloped virus containing double-stranded DNA. The child develops petechiae, hepatosplenomegaly, and jaundice. Brain calcifications are detected on computed tomography (CT). With which of the following viruses is the newborn most likely infected?
- A.
Cytomegalovirus
- B.
Hepatitis B
- C.
Hepatitis C
- D.
Hepatitis D
- E.
Herpes simplex
- 14.A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen. Which of the following is the most likely causative organism?
- A.
Legionella pneumophila
- B.
Listeria monocytogenes
- C.
Spirillium minus
- D.
Staphylococcus aureus
- E.
Streptococcus pneumoniae
- 15.A 33-year-old woman presents with fever, vomiting, severe irritative voiding symptoms, and pronounced costovertebral angle tenderness. Laboratory evaluation reveals leukocytosis with a left shift; blood cultures indicate bacteremia. Urinalysis shows pyuria, mild hematuria, and gram-negative bacteria. Which of the following drugs would best treat this patient's infection?
- A.
Ampicillin and gentamicin
- B.
Erythromycin
- C.
Gentamicin and vancomycin
- D.
Phenazopyridine and nitrofurantoin
- E.
Tetracycline
- 16.A newborn infant has multiple, hemorrhagic, cutaneous lesions and does not respond to sound. Head CT scan shows periventricular calcifications. Which of the following infectious agents is the most likely cause of this child's presentation?
- A.
Cytomegalovirus
- B.
Herpes simplex
- C.
Rubella
- D.
Syphilis
- E.
Toxoplasmosis
- 17.A very ill neonate has widespread granulomas. In utero infection with which of the following organisms is suggested by this finding?
- A.
Clostridium botulinum
- B.
Escherichia coli
- C.
Haemophilus influenzae
- D.
Listeria monocytogenes
- E.
Neisseria gonorrhoeae
- 18.A 37-year-old female presents to the emergency room with a fever. Chest x-ray shows multiple patchy infiltrates in both lungs. Echocardiography and blood cultures suggest a diagnosis of acute bacterial endocarditis limited to the tricuspid valve. Which of the following is the most probable etiology?
- A.
Congenital heart disease
- B.
Illicit drug use
- C.
Rheumatic fever
- D.
Rheumatoid arthritis
- E.
Systemic lupus erythematosus
- 19.A 4-year-old boy is brought to the emergency room in extreme respiratory distress, with a temperature of 103.8 degrees Fahrenheit. He is drooling and has difficulty swallowing, and on physical examination, inspiratory stridor is noted. A lateral x-ray shows swelling of the epiglottis. He has had no previous vaccinations. Which of the following agents is the most likely cause of these symptoms?
- A.
Haemophilus influenzae
- B.
Klebsiella pneumoniae
- C.
Legionella pneumophila
- D.
Mycoplasma pneumoniae
- E.
Streptococcus pyogenes
- 20.A 15-year-old boy presents to his physician with several weeks of slowly worsening pruritus of both of his feet. He is otherwise well and taking no medications. On examination, he has bilateral, erythematous, dry scaling lesions that are most obvious in the interdigital web spaces and on the soles. There is no bleeding or exudate. What would most likely be found in a potassium hydroxide (KOH) mount of a scraping of the affected skin?
- A.
Branching hyphae with rosettes of conidia
- B.
Branching, septate hyphae
- C.
Budding yeasts
- D.
Hyphae, arthroconidia, and blastoconidia
- E.
Pigmented, septate hyphal fragments
- F.
Short, curved hyphae and round yeasts
- 21.A 24-year-old AIDS patient develops chronic abdominal pain, low-grade fever, diarrhea, and malabsorption. Oocysts are demonstrated in the stool. Which of the following organisms is most likely to be the cause of the patient's diarrhea?
- A.
Diphyllobothrium latum
- B.
Entamoeba histolytica
- C.
Giardia lamblia
- D.
Isospora belli
- E.
Microsporidia
- 22.An African child develops massive unilateral enlargement of his lower face in the vicinity of the mandible. Biopsy demonstrates sheets of medium-sized blast cells with admixed larger macrophages. This type of tumor has been associated with which of the following?
- A.
Epstein-Barr virus and t(8;14)
- B.
Hepatitis B and t(9;22)
- C.
Herpesvirus and CD5
- D.
Human immunodeficiency virus and CD4
- E.
Human papillomavirus and t(2;5)
- 23.A 49-year-old Vietnamese man is diagnosed with tuberculosis. On physical examination, large flocculent masses are noted over the lateral lumbar back, and a similar mass is located in the ipsilateral groin. This pattern of involvement strongly suggests an abscess tracking along the
- A.
Adductor longus
- B.
Gluteus maximus
- C.
Gluteus minimus
- D.
Piriformis
- E.
Psoas major
- 24.A 36-year-old man with AIDS develops right-sided weakness involving the lower, but not the upper, limb. MRI scans reveal a ring-enhancing lesion within the white matter of the left frontal lobe. A biopsy shows coagulative necrosis of brain parenchyma with macrophage-rich chronic inflammatory infiltration admixed with microscopic cysts that contain characteristic bradyzoites. Which of the following is the most common source of this type of infection?
- A.
Anopheles mosquitoes
- B.
Bird droppings
- C.
Cats
- D.
Cooling systems
- E.
Washbasins
- 25.A 16-year-old girl presents with a painlessly enlarged lymph node in her right axilla. Peripheral blood counts are within normal limits. The lymph node is biopsied, and numerous granulomas filled with neutrophils and necrotic debris are observed. Which of the following organisms could produce this disease?
- A.
Bartonella henselae
- B.
Borrelia burgdorferi
- C.
Chlamydia psittaci
- D.
Coxiella burnetii
- E.
Rickettsia prowazekii
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