title: Minimum number of bacteria needed for antigen detection by counterimmunoelectrophoresis: in vivo and in vitro studies.
abstract: Threshold concentrations of Streptococcus pneumoniae type 3, Haemophilus influenzae type b, and Streptococcus sp. group B type Ib required for positive counterimmunoelectrophoresis reactions were determined in vivo and in vitro. Animals were infected intraperitoneally with various concentrations of microorganisms: adult mice with S. pneumoniae, suckling rats with H. influenzae, and 3-week-old mice with Streptococcus sp. group B. At 24 h after infection a minimum blood concentration of 10(3) colony-forming units (CFU)/ml was needed for S. pneumoniae or H. influenzae before antigen was detected in the serum. A minimum concentration of 10(6) CFU/ml was needed for Streptococcus sp. group B at 10 h after infection. Larger threshold concentrations (10(4) CFU/ml for S. pneumoniae, 10(5) CFU/ml for H. influenzae, and 10(7) CFU/ml for Streptococcus) were required in broth-grown cultures before cell-free antigens could be demonstrated by counterimmunoelectrophoresis in the medium. Marked levels of antigen release by group B streptococci were observed as the cultures entered early stationary phase. This study provides evidence of a long-accepted, though poorly substantiated, hypothesis that a threshold concentration of microorganism is necessary before counterimmunoelectrophoresis reactions become positive. Counterimmunoelecrophoresis results for clinical specimens should be interpreted cautiously in light of this evidence.
mesh_terms: D000818:Animals; D000833:Animals, Suckling; D000942:Antigens, Bacterial / Q000032:analysis*; D003378:Counterimmunoelectrophoresis; D006193:Haemophilus influenzae / Q000276:immunology; D007122:Immunoelectrophoresis; D051379:Mice; D051381:Rats; D018805:Sepsis / Q000276:immunology; D013292:Streptococcus agalactiae / Q000276:immunology; D013296:Streptococcus pneumoniae / Q000276:immunology
chemical_list: D000942:Antigens, Bacterial