Analysis of enterococci using portable testing equipment for developing countries – variance of Azide NutriDisk medium under variable time and temperature

This report compares the enterococci count on samples obtained with Azide NutriDisk (AND) (sterile, dehydrated culture medium) and Slanetz & Bartley (SB) medium when exposed to a variable in incubation time and temperature. Three experiments were performed to examine the recovery of enterococci on AND and SB media using membrane filtration with respect to: (a) incubation time; (b) incubation temperature; and (c) a combination of the two. Presumptive counts were observed at 37, 41, 46 and 47 °C and at 20, 24, 28 and 48 h. These were compared to AWWA standard method 9230 C (44 °C, 44 h). Samples were confirmed using Kanamycin Aesculin Azide (KAA) agar. Friedman's ANOVA and Students t-test analysis indicated higher enumeration of enterococci when grown on AND (p=0.45) than SB (p=<0.001) at all temperatures with a survival threshold at 47 °C. Significant results for AND medium were noted at 20 h (p=0.021), 24 h (p=0.278) and 28 h (p=0.543). The study concluded that the accuracy of the AND medium at a greater time and temperature range provided flexibility in incubator technology making it an appropriate alternative to SB medium for monitoring drinking water using field testing kits in developing countries.