Salmonella typhi is the causative agent of typhoid fever. The infective dose of S. typhi is:

Ans. (c) 102 - 105 bacilli Infective dose of salmonella varies from 200 to 106 colony forming units and the ingested dose is an impoant determinant of incubation period Organism Infective dose Shigella 10 - 1000 Vibrio >1010 (if source of infection is water) 102- 104 (if source of infection is food) Campylobacter jejuni 104 Yersinia enterocolitica 108- 109 EHEC 10 - 100