Volunteer studies are used to determine the infectious dose of Salmonella required to cause gastroenteritis. The curve obtained during the studies is shown in the diagram as line 2. Which of the following organisms could be represented by line 1 on this diagram?

Question

Volunteer studies are used to determine the infectious dose of Salmonella required to cause gastroenteritis.  The curve obtained during the studies is shown in the diagram as line 2.  Which of the following organisms could be represented by line 1 on this diagram?

Quizplus · Accepted Answer

11ec160b_3804_4ce9_9249_0d6d45de8b7c_MD0001_00 The 50% infectious dose (ID₅₀) corresponds to the minimum number of organisms required to cause disease in 50% of affected individuals. The organism in Line 1 has an ID₅₀ ~10². Depending on the age and condition of the host and on the species of Shigella, as few as 10 Shigella organisms can cause disease. For example, the ID₅₀ for S dysenteriae is 10, for S flexneri is 100, and for S sonnei is 500. Shigella is able to invade tissues and is highly adapted to surviving the acidity of the stomach and the bacteriostatic action of bile. The incubation period for shigellosis is 24-72 hours. Disease begins with watery diarrhea and progresses to fever, abdominal pain, dysentery, and tenesmus (painful rectal spasm associated with the urge to defecate but little passage of stool). A much larger inoculum of Salmonella (approximately 10⁷) is required for successful infection in a susceptible host. Other organisms that can cause diarrhea with only a small inoculum include Campylobacter jejuni (around 500 cells), Entamoeba histolytica (as few as 1-10 organisms), and Giardia lamblia (as few as 1-10 organisms). (Choices A, B, D, and E) In general, the ID₅₀ for Salmonella, Vibrio, Clostridium perfringens, and Escherichia coli are high (10⁴-10⁸). Educational objective: Depending on the age and condition of the host and the species of Shigella, as few as 10-500 cells can cause infection.

Volunteer Studies Are Used to Determine the Infectious Dose of Salmonella