A RAPID TEST TO DETECT ST-PRODUCING ESCHERICHIA-COLI IN FOOD

Pasteurized milk, liquid egg, minced meat, and various salads were artificially contaminated with varying numbers of cells from six Escherichia coli (E. coli) strains able to produce heat-stable enterotoxins (ST). The ST-producing E. coli were detected by the following procedure within 24 h without isolation by cultivation. After enrichment of the food sample in GN broth (4 h at 37-degrees-C), the material was transferred to brain heart infusion broth, incubated (16-18 h at 37-degrees-C), centrifuged (20 min, 7000 g) and heated to 80-degrees-C for 10 min, the supernatant was tested with the infant mouse test. The sensitivity (= ratio of detectable E. coli per total microbial numbers in the food sample) of the test procedure was high even in many food samples with a considerable competitive microbial flora. The procedure was used to test 419 routine food samples. Enterotoxigenic bacteria were found in 7 samples of liquid egg and 4 samples of salad. The test is recommended as a rapid screening test in food control.