Failure to detect cell-associated enterotoxin B in Staphylococcus aureus by immunofluorescence

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Staphylococcus aureus produces enterotoxin B, a significant virulence factor.
• Immunofluorescence is a common technique for detecting bacterial antigens.
• Protein A on S. aureus can non-specifically bind to the Fc region of intact immunoglobulin G (IgG).

Purpose of the Study:

• To investigate the suitability of intact IgG for detecting Staphylococcus aureus enterotoxin B on the cell surface using immunofluorescence.
• To evaluate the efficacy of F(ab(1))(2)-fragments of anti-enterotoxin B globulin for accurate antigen detection.
• To compare the detection limits of immunofluorescence and immunodiffusion for extracellular enterotoxin B.

Main Methods:

• Immunofluorescence assays using fluorescein isothiocyanate-labeled rabbit anti-enterotoxin B globulin (intact IgG) and F(ab(1))(2)-fragments.
• Testing both enterotoxin B-producing and -nonproducing Staphylococcus aureus strains.
• Quantitative comparison of extracellular enterotoxin B using immunodiffusion.

Main Results:

• Cell fluorescence was observed with intact IgG, likely due to protein A-IgG interaction, not cell-bound enterotoxin B.
• No cell-bound enterotoxin B was detected using F(ab(1))(2)-fragments of anti-enterotoxin B globulin.
• Immunofluorescence successfully detected soluble enterotoxin B, with immunodiffusion revealing approximately 1,000-fold higher extracellular levels compared to the cell fraction.

Conclusions:

• Intact IgG is unsuitable for detecting S. aureus cell surface antigens other than protein A in conventional immunofluorescence.
• F(ab(1))(2)-fragments of IgG are recommended for accurate immunofluorescence detection of bacterial antigens.
• This study highlights the importance of fragment selection in immunofluorescence to avoid non-specific binding artifacts.