Validation of Medi·Ca EC Method for AOAC Research Institute Certification.

A ready-made dry medium method for Escherichia coli and coliform count, the Medi·Ca EC method, was compared with the most probable number (MPN) method using Brilliant Green Lactose Bile broth and E. coli broth (AOAC INTERNATIONAL Official MethodSM 966.24) for seven food matrixes: raw beef, raw pork, raw frozen pork, raw lamb, raw salmon, frankfurter sausage, and cooked ham. The mean difference between the two methods at each contamination level for each matrix was <0.5 log10, and the 95% confidence intervals for the mean differences fell within the range of -0.5 to 0.5, with the exception of a few cases in the independent laboratory study. sr and RSDr values of the Medi·Ca EC method were generally lower than those of the MPN method, and r2 ranged from 0.91 to 0.99. Product consistency and stability studies showed little variability between production lots and the shelf-life of 20 months. An incubation time within the range of 22-26 h did not adversely affect the results; however, variations in sample volume did affect final counts. These results showed that the Medi·Ca EC method is a reasonable alternative to the reference method for the selected food matrixes and makes it possible to simultaneously detect and enumerate E. coli and coliform in only 24 h.