Endo Agar (NutriSelect Plus) is a selective and differential culture medium used for the isolation, cultivation, and differentiation of Gram-negative enteric microorganisms, specifically coliforms, from clinical and non-clinical samples. It is widely utilized in the microbiological examination of water, dairy products, and food.
Endo Agar was originally developed by Endo to differentiate between lactose-fermenting and non-lactose-fermenting intestinal bacteria. The selectivity of the medium is achieved through the inclusion of sodium sulfite and basic fuchsin, which inhibit the growth of Gram-positive bacteria. The medium is differential based on the ability of organisms to ferment lactose. When coliforms ferment lactose, the resulting acetaldehyde reacts with the sodium sulfite/fuchsin complex, releasing basic fuchsin. This colors the colonies red and, in the case of Escherichia coli, produces a characteristic metallic green sheen. Non-lactose fermenters remain colorless or pale pink.
Advantages
- Clear Differentiation: Provides a highly distinctive visual profile for E. coli, making presumptive identification straightforward.
- High-Quality Indicators: NutriSelect® Plus formulation ensures a stable color background and sharp, reproducible sheen development.
- Standardized Reference: Complies with international methods for the testing of water and dairy products.
- Versatile Application: Can be used for both direct streak inoculation and the membrane filtration method.
- Potent Inhibition: Effectively suppresses Gram-positive flora that could otherwise interfere with the analysis of enteric pathogens.
Interpretation of Results
| Microorganism | Colony Appearance | Interpretation |
|---|---|---|
| Escherichia coli | Red colonies with metallic green sheen | Lactose Fermenter (Coliform) |
| Klebsiella aerogenes | Pink to red, mucoid, no sheen | Lactose Fermenter (Coliform) |
| Salmonella typhimurium | Colorless to pale pink | Non-lactose fermenter |
| Staphylococcus aureus | Inhibited | Negative (-) |
Technical specifications
| Catalogue number | E5399 |
| Brand / Product Line | Sigma-Aldrich / NutriSelect Plus |
| Typical Composition (g/L) | Peptone (10.0); Lactose (10.0); K2HPO4 (3.5); Sodium sulfite (2.5); Basic fuchsin (0.5); Agar (15.0) |
| pH (at 25 °C) | 7.5 ± 0.2 |
| Preparation | 41.5 g/L |
| Storage Temperature | 15 – 25 °C |
Available packaging options
| E5399-500G | 500 g plastic bottle |
| Brand | Merck |
| Pack size | 500 g |
