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.

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

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

Explanation:

This is because the  infective  dose/ ID50 represented the  quantitative number of pathogenic organisms required to cause infection in 50% of adult human host exposed to it or infected  in a given route. The ID50 varies with the state of immune response of the subject in the experiental investigations , the strain of the pathogen involved , and  the route of administration .

The route is important because pathogens which  enter the host through oral route may be slowed down in biochemical,activities or even be killed, because of the acidity of the medium which may affect the ID50 of the pathogen.

Thus V, cholerae strain  with ID50  of 1,000,000 should be more virulent, causing faster  infection per 50 % of exposed adults subjects  than S.typhi of 10,000.