Date of Original Version
A rapid method was developed to quantify toxigenic Escherichia coli, using a membrane filter procedure. After filtration of samples, the membrane filter was first incubated on a medium selective for E. coli (24 h, 44° C) and then transferred to tryptic soy agar (3%; 6 h, 37° C). To assay for labile toxin-producing colonies, the filter was then transferred to a monolayer of Y-1 cells, the E. coli colonies were marked on the bottom of the petri dish, and the filter was removed after 15 min. The monolayer was observed for a positive rounding effect after a 15- to 24-h incubation. The method has an upper limit of detecting 30 toxigenic colonies per plate and can detect as few as one toxigenic colony per plate. A preliminary screening for these enterotoxigenic strains in polluted waters and known positive fecal samples was performed, and positive results were obtained with fecal samples only.
Calderon R. L., & Levin, M. A. (1981). Quantitative Method for Enumeration of enterotoxigenic Escherichia coli. J. Clin. Microbiol., 13(1), 130-134. Retrieved from http://jcm.asm.org/content/13/1/130.
Available at: http://jcm.asm.org/content/13/1/130