A 31-year-old man comes to the physician because of a 2-day history of abdominal pain and diarrhea. He reports that his stools are streaked with blood and mucus. He returned from a vacation in the Philippines 3 weeks ago. His vital signs are within normal limits. Abdominal examination shows hyperactive bowel sounds. A photomicrograph of a trichrome-stained wet mount of a stool specimen is shown. Which of the following organisms is the most likely cause of this patient's symptoms?
ACampylobacter jejuni
BGiardia lamblia
CCryptosporidium parvum
DShigella dysenteriae
EEntamoeba histolytica
A 10-year-old girl is brought to the emergency department because of a 2-day history of bloody diarrhea and abdominal pain. Four days ago, she visited a petting zoo with her family. Her temperature is 39.4°C (102.9°F). Abdominal examination shows tenderness to palpation of the right lower quadrant. Stool cultures at 42°C grow colonies that turn black after adding phenylenediamine. Which of the following best describes the most likely causal organism?
AGram-positive, anaerobic, rod-shaped bacteria that form spores
BGram-positive, aerobic, rod-shaped bacteria that produce catalase
CGram-negative, non-flagellated bacteria that do not ferment lactose
DGram-negative, flagellated bacteria that do not ferment lactose
EGram-negative, non-flagellated bacteria that ferment lactose
A 14-year-old boy presents with abdominal pain and diarrhea after returning from an East Asian vacation. Stool sample reveals the presence of red and white blood cells. Stool culture shows growth of immobile, non-lactose fermenting gram-negative rods. The attending physician explains to the medical students that the bacteria function by invading intestinal M-cells. The bacterium responsible for this patient's infection is:
AShigella dysenteriae
BSalmonella enteritidis
CHelicobacter pylori
DEscherichia coli
EVibrio cholerae
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