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A RAPID, SPECIFIC MEMBRANE FILTRATION PROCEDURE FOR ENUMERATION OF ENTEROCOCCI IN RECREATIONAL WATER
Citation:
Messer, J. AND A. Dufour. A RAPID, SPECIFIC MEMBRANE FILTRATION PROCEDURE FOR ENUMERATION OF ENTEROCOCCI IN RECREATIONAL WATER. Applied and Environmental Microbiology 64(2):678-680, (1998).
Description:
A two-step membrane filter (MP) method with mE medium, upon which the membrane must be incubated for 48 h and then transferred to a substrate medium to differentiate enterococci, is recommended by the U.S.Environmental Protection Agency to measure enterococci in fresh and marine recreational waters. The original mE medium was modified by reducing the triphenyltetrazolium chloride from 0.15 to 0.02 g/liter and adding 0.75 of indoxyl B-D-glucoside per liter. The new MF medium, mE1 medium, detected levels of enterococci in 24 h comparable to those detected by the original mF medium in 48 h, with the same level of statisticalconfidence. In addition, the use of mE1 medium eliminated the need to transfer the membrane to a substrate medium to differentiate enterococci from other genera of the fecal streptococcal group. Colonies from mE1 medium were examined to determine the rates of false-positive and false-negative occurrences, mEl medium had a false-positive rate of 6.0% and a false-negative rate of 6.5%. Interlaboratory testing of the MF method with mE1 medium demonstrated that the relative reproducibility standard deviations among laboratories ranged from 2.2% for marine water to 18.9% for freshwater. The comparative recovery studies, specificity determinations, and multilaboratory evaluation indicated that mE1 medium has analytical performance characteristics equivalent to those of mE medium. The simplicity of use and decreased incubation time with mE1 medium will facilitate the detection and quantification of enterococci in fresh and marine recreational waters.