Salmonella typhi is the causative agent of typhoid fever. What is the infective dose of S. typhi?

The infectious dose of Salmonella typhi causing typhoid fever is 10 3 - 10 6 colony forming units. Any conditions which decrease either the stomach acidity or intestinal integrity increases the susceptibility to Salmonella infection. Salmonella typhi and S. paratyphi is known to cause enteric fever. Salmonellae are gram-negative, non-spore-forming, facultatively anaerobic bacilli. They produce acid on glucose fermentation, reduce nitrates, and do not produce cytochrome oxidase. Salmonella infection begins with the ingestion of contaminated water. They causes enteric fever which is a systemic disease characterized by fever and abdominal pain. Ref: Harrison's Principles of Internal Medicine, 18e chapter 153, By David A. Pegues; Samuel I. Miller.