No abstract

Blastomyces dermatitidis evokes responses of human cellular immunity typical of other intracellular fungal pathogens. Differences in growth rates of intracellular Blastomyces yeast and the differences in amounts of yeast phagocytized by macrophages were determined for macrophages derived from peripheral blood monocytes from 11 persons with treated blastomycosis and 11 normal, healthy persons. Cellular immunity was examined by lymphocyte uptake of [3H]thymidine in response to a specific antigen of Blastomyces yeast. Yeast were more readily phagocytized by macrophages from the previously treated donors when compared with those from the normal donors; the yeast were confirmed to be intracellular by transmission electron microscopy. Likewise, a decrease in growth rates of yeast was demonstrable in cultures of macrophages from previously treated donors as compared with normal donors. This greater efficiency of phagocytosis and growth inhibition of B. dermatitidis reflects another mechanism of human cellular immunity to this fungal infection.

An enzyme immunoassay (EIA) for the capsular polysaccharide of Streptococcus pneumoniae type III was developed and applied to the measurement of this antigen in cerebrospinal fluid (CSF) in an experimental model of pneumococcal meningitis. EIA was performed by a single-antibody sandwich technique in which the globulin fraction of pneumococcal type-specific antiserum (antiserum-globulin) was used to coat the solid phase before antigen attachment and to conjugate with the labelling enzyme, horseradish peroxidase. Under optimum assay conditions EIA detected purified pneumococcal type-III capsular polysaccharide in concentrations as low as 0.15 ng/ml in aqueous buffer. Assayed by EIA, the mean concentration of type-III capsular polysaccharide in CSF of rabbits with pneumococcal meningitis increased exponentially from 24 h to 96nh of infection (range 13.9 ng/ml--62 500 ng/ml). Effective antimicrobial therapy of rabbits with meningitis was associated with a rapid decrease in the CSF concentration of the capsular antigen, although it was still detected in concentration in the range 1--10 ng/ml in 100% of animals treated for 4 days. Thus EIA provides a quantitative and extremely sensitive method of measuring type-III pneumococcal capsular polysaccharide in CSF.

One explanation for the failure of cephalothin to cure patients with bacterial meningitis is that desacetylcephalothin, as in vivo metabolite that has less antibacterial activity than the parent drug, penetrates more efficiently into cerebrospinal fluid (CSF); In experimental pneumococcal meningitis in rabbits, the peak levels of cephalothin and desacetylcephalothin in CSF after an intramuscular injection of 250 mg of cephalothin/kg were, respectively, 1.43 +/- 4.9 microgram/ml (2.8% of peak serum level) and 1.69 +/- 0.57 microgram/ml (2.2% of peak serum level). The observed half-life of desacetylcephalothin in CSF (3.32/hr) was longer (P less than 0.01) than that of cephalothin (0.72/hr). Choroid plexuses isolated from the lateral cerebral ventricles of rabbits with meningitis took up cephalothin in vitro more avidly than desacetylcephalothin (P less than 0.05), and metabolism of cephalothin to desacetylcephalothin by isolated choroid plexuses was demonstrated directly. Thus, intrathecal metabolism of cephalothin by the choroid plexus may contribute to the unsatisfactory performance of cephalothin in bacterial meningitis.

Rosaramicin, a new macrolide antibiotic, was compared with penicillin G in the treatment of pneumococcal meningitis in rabbits. Animals were infected intracistemally with 104 colony-forming units of Streptococcus pneumoniae type III (rosaramicin minimal inhibitory/bactericidal concentrations, 0.25/0.5 ,ug/ml; penicillin G miniimal inhibitory/bactericidal concentrations, 0.03/0.06 pug/ml). Treatment was instituted 96 h later. Infusion of rosaramicin at 25 mg/kg per h intravenously for 8 h produced a peak cerebrospinal fluid (CSF) drug concentration of 1.54 pug/ml (range, 0.87-3.6 pug/ml). During this infusion the numbers of pneumococci in CSF decreased from 6.2 ± 0.5 to 3.36 ± 1.12 logio colony-forming units per ml. Penicillin G, infused at 30 mg/kg per h for 8 h, reached a similar concentration in CSF but caused a greater reduction (P < 0.01) in CSF bacteria, from 6.4 ± 0.36 to 1.3 ± 0.67 logio colony-forming units per ml. Penicillin G, at 100 mg/kg per day intramuscularly for 5 days, cured 7 of 10 rabbits with pneumococcal meningitis. A higher dose, 300 mg/kg per day for 5 days, was no more efficacious: 11 of 14 rabbits were cured. Rosaramicin at 100 mg/kg per day intramuscularly for 5 days cured only 5 of 15 rabbits with meningitis, but a higher dosage regimen of that drug (250 mg/kg per day intramuscularly) produced acute, fuhminant enterocecitis and death within 48 h in seven of eight rabbits. No cytotoxin was detected in the feces of one rabbit with acute enterocecitis. Thus the efficacy of rosaramicin in experimental pneumococcal meningitis, measured by bacterial clearance from CSF and by treatment outcome, was less than that of penicillin G. In addition, high-dose parenteral rosaramicin caused acute, fulminant enterocecitis in a high proportion of treated rabbits.