The intracellular nature of Salmonella infection during the early stages of mouse typhoid.

In mouse enteric fever (typhoid) infection with S. typhimurium, the bacteria appear to grow intracellularly, and at least during the early phase of infection they are in splenic PMNs rather than macrophages. Inflammation caused by salmonella infection and other infections, such as MHV, results in inflammatory responses that enhance resistance to salmonella infection. At least in the case of MHV, this effect is most pronounced on the rate of salmonella growth. Since the effects of the Ity locus on salmonella growth rate are readily seen during the first few days of infection, when salmonella are primarily within PMNs, the Ity locus is able to mediate its effect on salmonella pathogenesis in PMNs in vivo. Whether or not macrophages play a predominant role in salmonella pathogenesis later in infection is not yet known.