Enumerate coliform organisms in water samples using Thermo Scientific™ Oxoid™ Membrane Endo Agar LES (Dehydrated) when used with basic Fuschin (BR0050). This membrane filtration medium is prepared according to the Lawrence Experimental Station formulation of McCarthy, Delaney and Grasso1 and used for the enumeration of coliform organisms in water2 using a 2-stage enrichment technique.
Use Membrane Endo Agar LES for enumeration of coliform organisms in water.
The value of the membrane filter technique for the enumeration of coliform organisms in water lies in its greater reliability and precision when compared with the MPN multiple tube test3. McCarthy, Delaney and Grasso1 have recommended a two-stage process of enrichment to provide a non-toxic environment for maximal resuscitation of the coliforms.
Calabrese and Bissonnette4 found that supplementation of M-Endo medium with catalase and sodium pyruvate resulted in improved recovery of coliform bacteria from chlorinated sewage effluent.
Experiments carried out by Noble5 indicated that sodium sulphite and Basic Fuchsin can be extremely detrimental to the stressed coliforms, reducing the total count.
Enrichment for a period of 2 hours ± 0.5 hours in single strength Lauryl Tryptose Broth CM0451 will give adequate resuscitation to the stressed coliform organisms and provide the best assessment of the quality of the drinking water.
Enrichment is usually not necessary for the examination of non-potable waters and sewage effluents.
Selection of the sample volume is governed by the expected bacterial density. An ideal quantity will result in growth of more than 50 coliform colonies and less than 200 colonies of all types.
All organisms which produce a colony with a golden-green metallic sheen within 24 hours incubation are considered members of the coliform group. The sheen may cover the entire colony or be restricted to the central area or the periphery. The recommended depth of M-Endo Agar LES in plates restricts the colony size and hence facilitates carrying out the colony count.
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