Prevention of radiation-induced bacteraemia by post-treatment with OK-432 and aztreonam

The effects of combined treatment with OK-432, an immunomodulator prepared from Streptococcus haemolyticus, and aztreonam, a monobactum antibiotic, in the prevention of radiation-induced bacteraemia and mortality were examined in ICR-MCH mice irradiated with 9.5 Gy. The organisms recovered from the irradiated mice were Streptococcus faecalis and Proteus mirabilis. Treatment with aztreonam reduced the incidence of mice infected with Proteus mirabilis (p < 0.01), but it showed no efficacy on Streptococcus faecalis. OK-432 could reduce the frequency of bacteraemia attributed to both organisms (p < 0.05). Combined treatment with OK-432 and aztreonam further decreased the incidence of bacteraemia by both organisms; no organisms were recovered at 14 days following irradiation. The survival rate at 30 days following irradiation was 80% in mice treated with OK-432 plus aztreonam and 55% with OK-432 alone, while it was 0% in the groups treated with aztreonam or saline alone. These results indicated that combined treatment with OK-432 and a suitable antibiotic such as aztreonam is more effective than OK-432 or aztreonam alone.