Synergistic effect of nonspecific immunostimulation and antibiotics in experimental peritonitis

To assess the role of combined immunomodulator and antibiotic therapy in sepsis, glucan--a beta 1,3 polyglucose--and gentamicin were administered in a model of murine peritonitis. ICR/HSD mice received one of four treatment regimens: 5% dextrose; gentamicin 0.02 mg intramuscularly (sub-MIC) 2 hours before peritonitis; glucan 0.1 mg intraperitoneally 24 hours before peritonitis; combined glucan-gentamicin treatment. All animals were challenged with 1 X 10(8) Escherichia coli intraperitoneally. Long-term survival was significantly enhanced in the combined therapy group (56%, p less than 0.05) when compared with D5W (0%), gentamicin alone (0%), or glucan alone (9%). Macrophage secretory activity, as assayed by interleukin-1 (IL-1) production, was significantly enhanced by combined therapy when compared with the other three treatment groups. Combined therapy significantly reduced E. coli bacteremia at 8 hours after inoculation, when compared with the other three groups. Availability of host neutrophils was assessed by peripheral counts and bone marrow proliferation assay. Combined glucan-gentamicin significantly enhanced bone marrow proliferation when compared with the other three groups and this enhancement correlated with increased circulating neutrophils. Combined immunomodulator and antibiotic therapy had synergistic effects on survival in E. coli peritonitis. This combined therapy enhanced macrophage secretory activity and bone marrow proliferation. Clinical use of immunomodulators may alter conventional use and dosage of antibiotics.