Question

Both Vibrio cholerae and Salmonella typhi are capable of causing disease inside of otherwise healthy individuals. The ID50 of V. cholerae is 1,000,000 cells, while the ID50 of S. typhi is 10,000 cells. Based on this information, which of the following statements is true?

a.Both V. cholerae and S. typhi are pathogenic, but V. cholerae is more virulent than S. typhi.
b.Both V. cholerae and S. typhi are pathogenic, but S. typhi is more virulent than V. cholerae.
c.S. typhi is pathogenic, while V. cholerae is non-pathogenic.
d.V. cholerae is pathogenic, while S. typhi is non-pathogenic.

Answer 1

Answer:

b.Both V. cholerae and S. typhi are pathogenic, but S. typhi is more virulent than V. cholerae.

Explanation:

$ID_{50}$ or 50% Infectious Dose  is the number of organisms (bacteria, viruses or fungi) required to produce disease in 50% of the hosts exposed to the organism.

An organism which has lesser $ID_{50}$ is said to be more virulent than the organism with greater $ID_{50}$. There is an inverse relation between 50% Infectious Dose and virulence.

Since both Salmonella typhi and Vibrio cholerae are able to infect  and produce disease so both of these organisms are pathogenic (able to cause disease). As lesser number of cells (10,000 cells) of Salmonella typhi are required to produce disease as compared to Vibrio cholerae (1,000,000 cells) so Salmonella typhi is more virulent than Vibrio cholerae.