Colony immunoblot assay for the detection of staphylococcal toxic shock syndrome toxin 1 (TSST-1) with anti-TSST-1 F(ab')2 fragments.
Toxic shock syndrome toxin 1 (TSST-1), an exoprotein of Staphylococcus aureus, is strongly implicated in the pathogenesis of TSS. Detection of TSST-1, however, is often hindered in immunoassays because of the cosecretion of protein A, a genetic trait which appears to be coordinately expressed with other exoproteins in S. aureus. We developed a colony immunoblot assay for rapid screening of TSST-1-producing S. aureus using TSST-1-specific rabbit F(ab')2 fragments. The sensitivity and specificity of this method were compared with those of a quantitative noncompetitive enzyme-linked immunosorbent assay (ELISA) for 34 S. aureus isolates (17 TSS-associated and 17 non-TSS-associated isolates). Cosecreted protein A in culture supernatants was evaluated by a quantitative competitive ELISA. The results clearly indicated the superiority of F(ab')2 fragments in eliminating nonspecific reactivity of protein A in the colony immunoblot assay. The sensitivity of the immunoblot with TSST-1-specific F(ab')2 was similar to that with whole immunoglobulin G (94 versus 82%, respectively; P = 0.601, Fisher's exact test), but the specificity was markedly improved (94 versus 59%, respectively; P = 0.039). Among TSST-1-negative isolates (as determined by ELISA), strains which gave false-positive results in the immunoglobulin G immunoblot assay produced higher amounts of protein A than strains which gave true-negative results (P = 0.08, Mann-Whitney rank sum test, one tailed). Among strains positive for TSST-1, the level of TSST-1 detected in culture supernatants correlated inversely with the amount of protein A secreted (rs = -0.64; P less than 0.01, Spearman rank correlation). These findings validate the utility of a rapid screening method for the detection of TSST-1-producing S. aureus and support the concept of coordinate secretion of exoproteins in S. aureus.
Department of Medicine, University of British Columbia, Vancouver, Canada.
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See
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Adilman
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Bartlett
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Chow
D001427:Bacterial Toxins; D004768:Enterotoxins / Q000032:analysis* / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D015151:Immunoblotting; D007140:Immunoglobulin Fab Fragments; D011237:Predictive Value of Tests; D012772:Shock, Septic / Q000382:microbiology*; D013205:Staphylococcal Protein A / Q000032:analysis; D013211:Staphylococcus aureus; D018089:Superantigens
D001427:Bacterial Toxins; D004768:Enterotoxins; D007140:Immunoglobulin Fab Fragments; D013205:Staphylococcal Protein A; D018089:Superantigens; C030107:enterotoxin F, Staphylococcal