Role of bacterial and host factors in the pathogenesis of Shigella septicemia

To determine the role of bacterial and host factors in the pathogenesis of shigellemia, blood and fecal Shigella isolates were compared for serum resistance and siderophore production, and shigellemic patients were examined for decreased serum bactericidal activity or increased serum transferrin saturation compared to control patients with non-bacteremic shigellosis. The majority of both blood (36/38) and fecal (36/48) Shigella isolates were sensitive to normal serum (greater than 2 log kill/60 min). Shigella dysenteriae type 1 strains were the most sensitive, and Shigella sonnei strains were the most resistant. Siderophore production was species- and serotype-dependent. Shigella dysenteriae type 1 produced only enterochelin; most Shigella flexneri expressed only aerobactin, and Shigella sonnei secreted both types of siderophores. No difference in siderophores was noted between blood and fecal strains within a given serotype. In contrast, shigellemic patients exhibited a 43-fold decrease in serum bactericidal activity and a two-fold increase in transferrin saturation compared to well-nourished control patients. These results indicate that the pathogenesis of Shigella septicemia is not related to serum resistance or siderophore production but may involve serum abnormalities associated with malnutrition.