1980 Volume 28 Issue 1 Pages 14-21
Opportunistic infection is an infection occurring in the host whose protective function has been decreased with a low virulent microorganism regarded usually as a nonpathogen. Most opportunistic pathogens are so low in virulence to the mouse that some treatment must be given to it to establish an experimental model for opportunistic infection.
To establish an experimental model for opprtunistic infection, leukopenia was induced by applying cyclophosphamide treatment to the mouse. Virulence of strains of various species to these mice was compared with that to nontreated control mice; senitivities of mice to the infecting organisms were compared by MLD values and their variances and therapeutic effects of antibiotics by ED50 values.
Leukocyte population of the mouse was normally 5, 000-6, 500 cells/cmm, which decreased to 900 cells/cmm in 4 days after administration of cyclophosphamide at a dose of 250 mg/kg. The sensitivities of the mouse to the infectious agent increased in parallel to the dose of cyclophosphamide.
The increased sensitivity differed depending upon the bacterial species; the sensitivity to Pseudomonas aeruginosa was the highest among glucose-nonfermenting gram-negative bacilli.
The effects of chemotherapy reflected the decreased protective function of the host. ED50 values of peroral penicillin, ampicillin, bacampicillin, and amoxicillin in Escherichia coil infection and those of carbenicillin and gentamicin in P. aeruginosa infection increased by 2-to 3-fold.
The above results confirmed that the host with decreased protective function is vulnerable to infection with a group of gram-negative bacilli regardad as opportunistic pathogens, and that chemotherapy becomes less effective in such cases that developing symptoms from infection.
