Demonstration of Escherichia coli heat-labile enterotoxin using bacterial cell sonicates.

Agar-plate colonies of Escherichia coli were suspended in 0.5 ml distilled water and sonicated for 15 s. The sonicate was tested for E. coli heat-labile enterotoxin by an enzyme-linked immunosorbent assay (ELISA). Sonication of enterotoxin-producing E. coli cells gave detectable toxin concentrations, which correlated well with the results obtained using culture broth supernatants for toxin detection in the ELISA. By using sonicates of isolated bacterial colonies from primary isolation agar plates, the subcultivation on agar plates or in culture broth tubes can be omitted. This may reduce the possibility of losing the plasmids coding for enterotoxin production. The time needed for analysis of suspected toxin producing E. coli strains will be reduced accordingly. Suspensions with bacterial counts of 10(6) per ml or more of E. coli, gave detectable levels of heat-labile enterotoxin in the sonicates.