Diagnosis of Neisseria infections by defined immunofluorescence. Methodologic aspects and applications.

Defined IF techniques have been used in our laboratories for the past 15 years for diagnosing meningococcal and gonococcal infections. Conjugates against these bacteria give desired specific staining (DSS) but also undersired specific staining (USS) due to cross-reacting antigens. USS is controlled by absorption. Nonspecific staining (NSS) of protein A-containing S. aureus caused by the reaction with the Fc part of the IgG molecule is blocked by adding RB 200-labeled antiS. aureus globulins to diluted FITC conjugates against gonococci or menigococci. Nss is also avoided by using FITC-labeled F(ab')2 fragments of IgG. By optimal labeling and separation of unlabeled FITC and heavily labeled molecules on Sephadex G-25 at low ionic strength and low pH, nonspecific reactions with tissues are reduced to a minimum. Defined IF can be utilized for diagnosing pathogenic Neisseria by examination of smears prepared from clinical specimens, as confirmative tests of oxidase-positive colonies, and for demonstrating these bacteria in tissue efflorescences and tissue biopsies. It is stressed that this technique should always be used in conjunction with conventional methods.