<prompt> Salmonella typhi is the causative agent of typhoid fever. The infective does of S.typhiOne bacillus108-1010 bacilli102-105 bacilli1-10 bacilli  <response>: Ans. is c i.e., 102-105 bacilli In human volunteer experiments, the infective dose was found to be 103-106 bacilli. Organism Infective dose . ETEC . EIEC . EHEC . Shigella . Campylobactor jejuni . Yersinia enterocolitica . Vibrio 106-101deg 108-10m 10-100 104 108-109 1010 if source of infection is water 102-104 if source of infection is food 