Salmonella typhi is a type of bacteria that causes typhoid fever, a serious illness primarily spread through contaminated food and water. It is part of the Salmonella genus, which includes other bacteria that can cause food poisoning. Symptoms of typhoid fever include high fever, weakness, stomach pain, and diarrhea or constipation. Once ingested, Salmonella typhi can invade the intestinal wall and enter the bloodstream, leading to systemic infection. Vaccines are available to help prevent typhoid fever, especially in areas where the bacteria are common. Proper sanitation and hygiene practices are essential to reduce the risk of infection.