USMLE (National Board) Practice Examination, Block One
A 9-year-old girl was playing soccer when she began to limp. She has a pain in her leg and points to her upper thigh when asked where it hurts. Her temperature is 101°F. X-ray of the femur reveals that the periosteum is eroded. You order a blood culture. Which one of the following would be the MOST likely blood culture findings?
(A) Gram-negative rods that grow on EMB agar, forming purple colonies and a green sheen
(B) Gram-positive cocci that grow on blood agar, causing a clear zone of hemolysis, and are coagulase-positive
(C) Gram-positive rods that grow only anaerobically and form a double zone of hemolysis on blood agar
(D) Gram-negative diplococci that grow on chocolate agar, are oxidase-positive, and ferment maltose
(E) Gram-positive cocci that grow on blood agar, causing a green zone of hemolysis, and are not inhibited by optochin and bile
Your summer research project is to study the viruses that cause upper respiratory tract infections. You have isolated a virus from a patient’s throat and find that its genome is RNA. Furthermore, you find that the genome is the complement of viral mRNA within the infected cell. Of the following, which one is the MOST appropriate conclusion you could draw?
(A) The virion contains a polymerase.
(B) The purified genome RNA is infectious.
(C) The genome RNA is segmented.
(D) A single-stranded DNA is synthesized during replication.
(E) The genome RNA encodes a precursor polypeptide that must be cleaved by a protease.
A 25-year-old man has a history of four episodes of boils in the last year. Boils are abscesses caused by Staphylococcus aureus. Which one of the following is MOST likely to be the underlying immunologic factor that predisposes him to multiple episodes of boils?
(A) A deficient amount of the C8 component of complement in his plasma
(B) An inability of his macrophages to present antigen in association with class I MHC proteins
(C) A failure to release granzymes from his cytotoxic T cells
(D) An insufficient amount of IgG in his plasma
You are reading an article that says that otitis media is commonly caused by nonencapsulated strains of Haemophilus influenzae. You ...