Comparative study of several culture media to determine coliforms and E. coli in dairy and cocoa products

Five culture media have been evaluated for the detection of coliforms, E. coli, and Enterobacteriaceae in several varieties of dairy products (fresh and dehydrated) and dehydrated cocoa products. Those media were: Brilliant green bile, Lauryl sulfate tryptone, Lactose glutamic acid, Enteric Enrichment broth, and Lactose broth. The medium with the highest sensitivity to coliforms detection was Lactose glutamic acid broth. Several times Brilliant green bile, Lactose or Enteric Enrichment broth were significantly less sensitive than the other two media. Except once, when it was significantly better, Lauryl sulfate broth was not significantly different from the other media. False positive results were most frequently found during the examination of dairy products with Lactose glutamic acid and Lactose broth, consequently confirmation reactions have to be carried out when these media are used. Frequently, Enteric Enrichment broth was less satisfactory for the detection of Enterobacteriaceae than the other media used. All five media showed more coliforms after 48 h than after 24 h of incubation at 30 degrees C. Whenever a significant difference existed in the sensitivity to determine E. coli, Lactose glutamic acid broth was significantly better than the other media.