Enhanced susceptibility of mice with streptozotocin-induced diabetes to type II group B streptococcal infection

Abstract

Since diabetes mellitus predisposes adults to group B streptococcal (GBS) bacteremia, a murine model of streptozotocin-induced diabetes and type II GBS bacteremia was developed to assess certain immune factors which might influence susceptibility to infection. In diabetic mice, the 50% lethal dose for two strains of type II GBS was significantly lower (greater than 1 log10 decrease in CFU per milliliter) than in control animals. This enhanced virulence of GBS for diabetic animals was associated with prolonged bacteremia, persistent sequestration of organisms in the splanchnic reticuloendothelial system, and a shift from splenic to hepatic clearance. Although immunization of control and diabetic animals resulted in high concentrations of type-specific serum antibody, it had no effect on late reticuloendothelial system sequestration in diabetics. In contrast, depletion of complement by treatment of mice with cobra venom factor blocked reticuloendothelial system clearance and resulted in fatal infection in both diabetic and control mice. These results indicate that neither type-specific antibody nor an intact complement system is adequate for effective clearance of type II GBS bacteremia in mice with experimentally induced diabetes. This clearance deficit could be the result of a defect in hepatocyte membrane receptors necessary for removal of this encapsulated microorganism.