49940 Millipore

ONPG Disks

for microbiology

Synonym: β-Galactosidase Test Disks, 2-Nitrophenyl-β-D-galactopyranoside Disks

  •  NACRES NA.85



Related Categories Discs, Strips and Cards, Identification Tests & Reagents, Indicator Organisms, Microbiology
Quality Level   100
grade   for microbiology
shelf life   limited shelf life, expiry date on the label
application(s)   microbiology: suitable (microbial identification)
Featured Industry   Environmental
Food and Beverages
shipped in   wet ice
storage temp.   2-8°C
suitability   bacteria


General description

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.


Sterile filter paper discs (50 pcs, diameter 6 mm) impregnated with o-nitrophenyl-β-D-galactopyranose

Safety & Documentation

Safety Information

Personal Protective Equipment 
NONH for all modes of transport
WGK Germany 
Flash Point(F) 
Not applicable
Flash Point(C) 
Not applicable


Certificate of Analysis (COA)

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Protocols & Articles


Differentiation of Escherichia coli from coliforms

In August 2008, the discovery of E. coli-contaminated beef in the United States prompted a nationwide recall of beef. The source turned out to be one supplier that had a history of contamination of i...
Jvo Siegrist
AnalytiX Volume 8 Article 5
Keywords: Decarboxylations, Fermentation, Genetic, Indicators, Microbiology, Reductions

Identification of Microorganisms Based on Color

For microbiologists the most fundamental stain was developed in 1884 by the Danish bacteriologist Hans Christian Gram. The Gram Stain allows the determination of morphology, dividing bacteria into tw...
Jvo Siegrist
Microbiology Focus Edition 1.4, Product Manager Microbiology....
Keywords: Antibiotics, Enzyme activity, Fermentation, Gram stain, Help, Indicators, Reductions

Microbiology Introduction

An initial aim of all microbiologists is the reproducible growth of their microbial cultures, no matter whether the microorganisms are of natural origin or have been genetically engineered by man. Re...
Keywords: Absorption, Aerobic, Anaerobic, Antibiotics, Antimicrobials, Buffers, Culture media, Diffusion, Environmental, Filtration, Genetic, Growth factors, Metabolism, Phase transitions, Precipitation, Reductions, Respiration, Sample preparations, Vitamins

Vibrio Detection

Vibrios are motile, curved or comma-shaped bacilli and have a single polar flagella with sheet proteins. They are often found in open water, freshwater and saltwater. Vibrios are facultative aerobe a...
Jvo Siegrist
Microbiology Focus Edition 1.3
Keywords: Dehydration reaction, Diagnostic, Fermentation, Indicators, Metabolism, Microbiology

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