Evaluation of Sanita-kun E. coli & Coliform Sheet Medium for the Enumeration of Total Coliforms and E. coli

Abstract

The Sanita-kun E. coli & Coliform sheet medium consists of a transparent cover film, an adhesive sheet, a layer of nonwoven fabric, and a water-soluble compound film, including a culture medium formula for the enumeration of total coliforms and differentiation of Escherichia coli. The Sanita-kun E. coli & Coliform sheet is a chromogenic medium and contains X-Gal, which is hydrolyzed by beta-galactosidase from coliforms to produce a visible blue dye and Salmon-glucuronic acid, which is hydrolyzed by beta-glucuronidase from E. coli to produce a red-purple dye. It is easy to distinguish the difference between E. coli and coliform (other than E. coli) colonies. Total coliforms and E. coli can be enumerated by incubating the sheet medium at 35 + 1 degrees C for 21-24 h without further confirmation. The Sanita-kun E. coli & Coliform sheets were validated as a medium for the enumeration of E. coli and total coliform in meats and meat products using processed meat and two types of raw and frozen meats using stomacher and blender homogenization. In the stomacher homogenization, all 100 samples showed no significant difference between Sanita-kun sheet and AOAC Method 966.24. The linear correlation coefficients (r2) were calculated as 0.90 (coliform) and 0.79 (E. coli). In the blender homogenization, out of 100 samples tested, 99 showed no significant difference between Sanita-kun sheet and AOAC Method 966.24, but the count of total coliforms of Sanita-kun in one sample of uninoculated raw beef was significantly higher than that obtained by AOAC Method 966.24. The linear r2 values were calculated as 0.84 (coliform) and 0.86 (E. coli). The inclusivity and exclusivity study indicated an inclusivity rate of 100% and an exclusivity rate of 95.4%. The sensitivity study showed positive results when the homogenate or dilution contained 3 CFU/mL of coliform or E. coli. The performance of four different lots of the sheets was equivalent, and suggested no change of the performance at least for 3 years at 2-15 degrees C. The Sanita-kun E. coli & Coliform sheet medium has been granted Performance Tested Method status.