Immunofluorescent detection of enterotoxin B from S. Aureus

Abstract The well-known fact that many Staphylococcus aureus strains react with antisera to other bacteria and normal sera has been a major problem in immunofluorescent detection of various bacterial antigens. A reaction between protein A and the Fc-portion of IgG from different species is now well documented. Staphylococcal strains with a high content of protein A reacted strongly with FITC-labelled IgG from nonimmunized rabbits and rabbits immunized against various bacterial antigens. Pepsin digestion of the IgG eliminated the nonspecific reaction thus showing that the Fc-part of the IgG is involved. The specific immunological activity of the F(ab 1 ) 2 -fragments was intact. FITC-conjugated IgG and F(ab 1 ) 2 from rabbits immunized with purified enterotoxin B was used for detection of enterotoxin B with immunofluorescence. S. aureus strains with a high production of enterotoxin B and protein A, reacted in immunofluorescence with IgG but not F(ab 1 ) 2 . Enterotoxin B positive but protein A negative strains failed to react with IgG or F(ab 1 ) 2 . In all experiments antigonococcal IgG were included before pepsin digestion and conjugation as a control. In this system the same titre was recorded with both IgG and F(ab 1 ) 2 . The findings suggest that enterotoxin B is not detectable on the surface of S. aureus with immunofluorescence methods in current use.