Salmonellae are a Gram-negative, flagellated, facultative anaerobes of the family Enterobacteriaceae (Giannella; Morphology). They are, small, rod-shaped bacilli, with a polysaccharide capsule characterized by their O, H and V antigens. The organisms produce H2S from inorganic sulfur and produce acid and gas from glucose, with the exception of S. typhi which is a non-gas producer and only produces minimal H2S. Salmonella are relatively resistant to bile salts and this trait can be utilized for selective isolation media. They reduce nitrates (NO3 to NO2 or all the way to N2) and are oxidase negative. Salmonella do not ferment lactose. They are endergonic, using glucose for energy. The bacteria are readily isolated from stool specimens or rectal swabs on selective/differential agar media (e.g. XLD, XLT-4, SS or brilliant green agar supplemented with novobiocin.
There were over 2501 recognized strains of Salmonellae identified as of 2004, but human infections are caused almost exclusively by serotypes Salmonella typhi and Salmonella paratyphi which cause enteric fever, Salmonella typhimurium which causes enteritis, Salmonella enteritidis which causes enteritis, and Salmonella choleraesuis which causes septicemia (Barrali; Morphology; World). Taxonomically, all strains of Salmonellae fall within one species, S. enterica, but they continue to be recognized by species names. The optimum growth temperature for most Salmonellae serotypes, including S. typhi, is 35 to 37C, with a minimum of 7C and a maximum of 45C for S. typhi and 49.5C for other non-typhoid salmonellae (Non-typhoid; Samonellae). The optimum pH for growth is 7 to 7.5 for both types, with a minimum of 3.8 and a maximum of 9.5. They are facultative anaerobes so can grow with or without the presence of air. They can grow under nitrogen at a rate only slightly less than their growth under air.
S. typhi can survive for 230 days on sweets and for 4 day...