Microbiological Assay of the β‐Exotoxin of Bacillus thuringiensis

Summary. The β‐exotoxin of Bacillus thuringiensis var. thuringiensis suppressed the growth of Sarcina flava and certain other bacteria. The antibacterial effect on S. flava was correlated with the amount of exotoxin as determined by absorption at 260 nm as well as to the toxic response in bioassays using the larvae of the housefly. Growth inhibition of S. flava could be shown in cup plate assay of the cellfree supernatant of B. thuringiensis var. thuringiensis cultures, prepurified and purified β‐exotoxin. The results showed that it was possible to use S. flava in a quantative assay of the β‐exotoxin activity of B. thuringiensis.