Development and application of immunochromatographic tests for the detection of staphylococcal enterotoxin E

Abstract

Two rapid immunochromatographic assay formats for the detection of Staphylococcus aureus enterotoxin serotype E (SEE) were developed. For both tests, polyclonal antibodies against SEE were immobilized on a membrane strip representing the test zone, while second anti-SEE antibodies conjugated to dyed latex particles were employed as markers in sandwich immunoassay. In a two-step test format, sample and labelled antibodies were preincubated prior to immunochromatography, whereas in a one-step test the labelled antibodies were integrated in the test pad and activated by addition of the sample solution. In the presence of SEE in a sample solution, colour development at the antibody-coated zone occured within 20 min. The visual detection limits for SEE in buffer solution were at 5 ng ml-1 (two-step test) and at 10 ng ml-1 (one-step test), respectively. Both assays were specific for SEE and showed no cross-reaction with serotype A, B, C, and D enterotoxins. When the two-step test format was used for the identification of SEE in S. aureus culture broth, the detection limit was found to be 10 ng ml-1. Culture supernatants of 10 enterotoxigenic strains of S. aureus were analysed with the immunochromatographic two-step test and with a microtitre plate enzyme immunoassay (EIA) test kit for enterotoxins A-E. Results obtained by the immunochromatographic test (presence or absence of SEE) were in excellent agreement with those of the microtitre EIA.