ONPG Disks are used to detect the presence of β-galactosidase, an enzyme found in lactose-fermenting organisms. Lactose utilization depends upon two enzymes: β-galactoside permease, which catalyzes transport of lactose into the cell, and β-galactosidase, which breaks down lactose into galactose and glucose. β-Galactosidase is not lactose specific and can act on simple galactosides including the ONPG (o-nitrophenyl-β-D-galactopyranose) substrate. ONPG hydrolysis results in the release of galactose, and the yellow chromogenic compound, o-nitrophenol. The test substrate, ONPG, does not depend on an induced or constitutive permease enzyme to enter the cell, therefore reactions are rapid and occur within a 24-hour period even for late lactose fermenters.
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Sterile filter paper discs (50 pcs, diameter 6 mm) impregnated with o-nitrophenyl-β-D-galactopyranose
Most studies on Salmonella enterica serovar Typhimurium infection focus on strains ATCC SL1344 or NTCC 12023 (ATCC 14028). We have compared the abilities of these strains to induce membrane ruffles and invade epithelial cells. S. Typhimurium strain 12023 is less
There are many other methods of detection to indicate the presence of E. coli. Review common tests and biochemical reactions for this contaminant.
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