United State Medical Licensing Examination (Step 1) Set 15

A 30-year-old previously healthy patient has all the gastrointestinal symptoms of infection with hepatitis A virus (HAV), yet all the tests for HAV-IgG and HAV-IgM are negative. Which of the following is the most likely cause of this infection?

In a quantitative serological test, the results shown below were obtained (+ = antibody detected, 0 = no antibody detected). Which of the following courses of action should be taken?

A Gram-stain smear of spinal fluid from a 2- year-old child reveals short gram-negative rods. It grows on enriched chocolate agar, but does not grow on blood agar, except adjacent to a streak of staphylococci. The organism most probably is which of the following?

Clinical laboratory results indicate that an AIDS patient in a county hospital in San Antonio is infected with an acid-fast bacillus. Which of the following bacteria is this organism most likely to be?

Within hours after being bitten by a cat trapped in a flood drain, a member of the rescue team develops redness, swelling, and intense pain at the site of the bite. Laboratory results indicate the presence of mixed flora in the wound, including a gram-negative rod that is frequently associated with cat and dog bites and that often leads to complications such as osteomyelitis if untreated. Which of the following is most likely to be this organism?

Which of the following immunoglobulins is responsible for passing the placental barrier and attacking the Rh+ fetal red blood cells in hemolytic disease of the newborn (erythroblastosis fetalis)?

A 27-year-old man was treated with penicillin for gonorrhea. Thirty-five days later he was reinfected with the same germ, and his physician administered an intramuscular dose of penicillin. Two minutes following the injection of penicillin, the patient experienced hypotension and shock and became unconscious. This reaction was most likely mediated by which of the following?

A 78-year-old patient with an episode of acute urinary retention was catheterized. Three days later, he developed fever and suprapubic pain. Culture of the urine revealed a thin film of bacterial growth over the entire blood agar plate, and the urease test was positive. Which of the following is the most likely organism to cause this infection?

A similar virus was isolated from several students in a day-care school that experienced a respiratory disease outbreak. This virus passes through a 50 nm filter, grows best in human diploid fibroblasts at 33

Sputum from a patient with a respiratory infection reveals bacteria that resist engulfment by phagocytic WBCs. Which of the following factors is most likely responsible for this virulence?