Influence of various immunosuppressive agents on the occurrence of endogenous bacteraemia in mice

The influence of six immunosuppressive agents on the occurrence of endogenous bacteraemia in mice was evaluated. The mortality rates in conventional ddY mice given cyclophosphamide (CY), fluorouracil (5-FU), methotrexate (MTX), cisplatin (CDDP) or FK-506 intraperitoneally, or dexamethasone (DXM) subcutaneously were 70, 100, 100, 100, 0 and 0%, respectively. Pseudomonas aeruginosa was isolated from 70% of mice treated with CY but from only 10% of mice treated with 5-FU and 30% treated with MTX. Enterobacteria were isolated from 90% of mice treated with 5-FU. Specific-pathogen-free (SPF) mice fed P. aeruginosa were also treated with these agents. All mice in the CY, 5-FU, MTX and CDDP groups died whereas mice treated with DXM and FK-506 showed 20% and 0% mortality, respectively. Pure cultures of P. aeruginosa were obtained from all of the mice treated with CY. Polymicrobial bacteraemia with P. aeruginosa and enterobacteria occurred in 5, 25, 5 and 5% of mice treated with 5-FU, MTX, CDDP and DXM, respectively. Enterobacterial bacteraemia was observed in 70% of mice treated with CDDP and in 5% of the DXM group. Different types of bacteraemia were induced by different immunosuppressive agents. The mechanism of immunosuppression may affect the frequency of bacteraemia and the causative organism.