A 19-year-old male college student presents to the student health department with abdominal pain, diarrhea, and fever. He says that his symptoms started 1 day ago. He has had 10 stools in the past day and has noted blood mixed in with the stool on several occasions. He usually eats at home but reports having eaten chicken in the college cafeteria days ago. He has no history of gastrointestinal (GI) disease. On examination, he has a temperature of 37.8°C and appears to be in pain. His abdomen has hyperactive bowel sounds and is diffusely tender but without rigidity, rebound tenderness, or guarding. A stool sample tests positive for blood and fecal leukocytes. Stool cultures are sent and subsequently positive for a pathogenic organism. The causative agent recovered from feces was a slightly curved, gram-negative rod.
What is the most likely pathogenic organism?
In what atmospheric environment does this organism grow?
Case 2
A 30-year-old dairy farmer was in good health until the day prior to admission when he felt chilled and feverish. He developed nausea, vomiting, diarrhea, and lower abdominal discomfort and presented to the emergency room, where he was noted to be lethargic. His vital signs included a temperature of 40°C. His physical examination was remarkable for lower abdominal tenderness to palpation bilaterally. A rectal examination revealed occult blood in the stool. The patient was lethargic but had no focal neurological deficits. Of note, his 3-year-old child had been discharged from the hospital 2 days previously with a similar history.
The patient underwent a lumbar puncture because of his altered mental status and fever. Laboratory studies of cerebrospinal fluid (CSF) were within normal limits, and a bacterial culture of CSF was negative.
A stool examination for fecal leukocytes was positive, and stool culture was diagnostic. Biochemical examination of the organism revealed it to be a lactose nonfermenter on MacConkey agar, H2S negative, urea negative, and nonmotile at both 25 and 37°C.
On the basis of the biochemical reactions, which organism do you think this is?
Did the person have meningitis? Explain your answer.
What was the most likely source(s) of infection?
Case 3
A 48-year-old man presents to the emergency department with 2 days of crampy abdominal pain, nausea, vomiting, diarrhea, and fever. He has not had any blood in his stool. He denies contact with anyone with similar symptoms recently. He has not eaten any raw or unprocessed foods recently. The only food that he did not prepare himself in the past week was a breakfast of eggs "sunny side up" and bacon that he had at a diner the day before his symptoms started. On examination, he is tired appearing; his temperature is 37.7°C. The physician interprets a positive "tilt test," indicating significant volume depletion. His abdominal examination is notable for diffuse tenderness.
A MacConkey agar plate culture results in the following biochemical reactions:
TSI K/A with H2S, citrate positive, and urea negative. The serological tests were positive for this pathogen.
On the basis of the biochemical reactions, which organism do you think this is?
What are the most common sources of human infections with this organism?