title: Standardization of Neisseria meningitidis serogroup B colorimetric serum bactericidal assay.
abstract: The correlate of protection for serogroup B meningococci is not currently known, but for serogroup C it is believed to be the serum bactericidal assay (SBA). The current SBAs are labor intensive and the variations in protocols among different laboratories make interpretation of results difficult. A colorimetric SBA (cSBA), based on the ability of Neisseria meningitidis serogroup B to consume glucose, leading to acid production, was standardized by using group B strain Cu385-83 as the target. The cSBA results were compared to those obtained for a traditional colony-counting microassay (mSBA). Glucose and bromocresol purple pH indicator were added to the medium in order to estimate growth of cSBA target cell survivors through color change. Different variants of the assay parameters were optimized: growth of target cells (Mueller Hinton agar plates), target cell number (100 CFU/per well), and human complement source used at a final concentration of 25%. After the optimization, three other group B strains (H44/76, 490/91, and 511/91) were used as targets for the cSBA. The selection of the assay parameters and the standardization of cSBA were done with 13 sera from vaccinated volunteers. The titers were determined as the higher serum dilution that totally inhibited the bacterial growth marked by the color invariability of the pH indicator. This was detected visually as well as spectrophotometrically and was closely related to a significant difference in the growth of target cell survivors determined using Student's t test. Intralaboratory reproducibility was +/-1 dilution. The correlation between bactericidal median titers and specific immunoglobulin G serum concentration by enzyme immunoassay was high (r = 0.910, P < 0.01). The bactericidal titers generated by the cSBA and the mSBA were nearly identical, and there was a high correlation between the two assays (r = 0.974, P < 0.01). The standardized cSBA allows easy, fast, and efficient evaluation of samples.
authors.affiliation: Department of Basic and Clinical Immunology, Finlay Institute, 27 avenue #198 and 202, La Lisa, P.O. Box 16017, Havana City, Cuba. trodriguez@finlay.edu.cu
authors.forename: Tamara
authors.initials: T
authors.lastname: Rodríguez
authors.forename: Miriam
authors.initials: M
authors.lastname: Lastre
authors.forename: Barbara
authors.initials: B
authors.lastname: Cedré
authors.forename: Judith
authors.initials: J
authors.lastname: del Campo
authors.forename: Gustavo
authors.initials: G
authors.lastname: Bracho
authors.forename: Caridad
authors.initials: C
authors.lastname: Zayas
authors.forename: Carlos
authors.initials: C
authors.lastname: Taboada
authors.forename: Miriam
authors.initials: M
authors.lastname: Díaz
authors.forename: Gustavo
authors.initials: G
authors.lastname: Sierra
authors.forename: Oliver
authors.initials: O
authors.lastname: Pérez
mesh_terms: D000293:Adolescent; D000328:Adult; D001770:Blood Bactericidal Activity; D003124:Colorimetry; D003165:Complement System Proteins / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D009345:Neisseria meningitidis / Q000145:classification / Q000276:immunology*; D012680:Sensitivity and Specificity; D012703:Serotyping
chemical_list: D007074:Immunoglobulin G; D003165:Complement System Proteins