A simple assay to detect Escherichia coli producing heat labile enterotoxin: results of a field study of the Biken tests in Bangladesh.

In the Biken test a precipitin line forms in the agar between an Escherichia coli colony producing heat-labile enterotoxin (LT) and anti-cholera-toxin or anti-LT sera placed in an adjacent well. E. Coli isolates form 273 unselected patients with diarrhoea and 516 stock cultures of known toxin type were screened blindly for LT production by means of the Biken tests and the standard Chinese hamster ovary (CHO) cell assay. The Biken tests was 98% sensitive and 99% specific. All results of the Biken test which did not accord with the CHO cell assay were attributable to mixed stocks of LT-producing and non-LT-producing E. coli strains. The Biken test performed on agar plates with commercially available reagents offers clinical laboratories in developed and developing countries a simple, reliable, and inexpensive method of diagnosing diarrhoea caused by LT-producing strains of E. coli.