Detection by a staphylococcal coagglutination test of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli.

For detection of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli, the staphylococcal coagglutination test reported by Brill et al. (J. Clin. Microbiol. 9:49-55, 1979) was modified to give better results. Staphylococcal cells were sensitized with anti-heat-labile enterotoxin antiserum and suspended in phosphate-buffered saline containing 0.5% bovine serum albumin, 0.05% Tween 80, 0.01% gelatin, and 0.02% NaN3. The test strain was cultured in 0.25 ml of Biken broth no. 2 in a test tube (12 by 100 mm) stood at an inclination of about 10 degrees to the horizontal. After incubation for 5 h at 37 degrees C, the cells were collected by centrifugation at 2,500 rpm for 15 min and suspended in 50 microliters of polymyxin B solution (20,000 IU/ml). The suspension was then incubated for 1 h at 37 degrees C and centrifuged at 2,500 rpm for 15 min, and 10 microliters of the supernatant was used for the test on a slide. The results of the modified test correlated completely with those obtained by the Biken test. The modifications of the staphylococcal coagglutination test described here allow for detection of heat-labile enterotoxin-producing enterotoxigenic E. coli within 6 to 7 h after inoculation of a test strain.