Universal Filter Membrane Medium (without Membrane Filter)

Principle And Interpretation

Field of Application: Water, waste water, pharmaceuticals, cosmetics, packing materials and other clinical test materials. DriFilter Membrane Nutrient Pad Medium is ready to use sterile culture media in the form of a 50 mm biological inert absorbent pads impregnated with HiChrome Universal Differential medium, then dried and sterilized in 55 mm petri plate. They eliminate the need of laborious media preparation and autoclaving procedures. The nutrient pads are to be just rewetted with sterile distilled water and are ready to use. Use of nutrient pads allows larger sample volumes to be tested at a time. Interpretation of results is directly by counting the CFUs and also quantifies the microbial load present in the sample. HiChrome Universal Differential Medium is a modification of the medium formulated on basis of the work carried out by Pezzlo (1), Wilkie et al (2), Friedman et al (3), Murray et al (4), Soriano and Ponte (5) and Merlino et al (6). HiChrome Universal Differential Medium is recommended for the presumptive identification of microorganisms from clinical and non-clinical specimens where the medium has broader application as a general nutrient agar for isolation of various microorganisms. This medium helps in the identification of some gram-positive bacteria and gram-negative bacteria on the basis of different colony colours exhibited by them. These colours are formed due to the reactions of genus or species specific enzymes with the two chromogenic substrates incorporated in the medium. Enterococcus species, Escherichia coli and coliforms produce enzymes which specifically cleave these chromogenic substrates to give characteristically distinctive colony colours. Peptones in the medium serve as sources of amino acids like phenylalanine and tryptophan which aids in indicating tryptophan deaminase activity, thereby facilitating the identification of Proteus species, Morganella species and Providencia species. One of the chromogenic substrate is cleaved by B-glucosidase enzyme possessed by Enterococci resulting in the formation of bluish green colonies. Escherichia coli possesses the enzyme ẞ- galactosidase which specifically cleaves the other chromogenic substrate resulting in the formation of purple coloured colonies. Escherichia coli can be differentiated and confirmed from other similar coloured colonies, by performing the indole test. Coliforms cleave both the chromogenic substrates forming blue to purple coloured colonies. Colonies of Proteus, Morganella and Providencia species appear brown due to tryptophan deaminase activity.Peptic digest of animal tissue and casein enzymic hydrolysate provide nitrogenous, carbonaceous compounds, essential growth nutrients and also serve as a source of amino acids.