MacConkey Broth Purple is designed for the presumptive identification of coliforms. The medium contains ox bile, which inhibits the growth of Gram-positive organisms, ensuring the selection of Gram-negative enteric bacteria. Lactose serves as the fermentable carbohydrate source. When coliforms ferment lactose, they produce acid and gas. The acid production causes the pH indicator, bromocresol purple, to change color from purple to yellow. Gas production is typically detected using an inverted Durham tube. As part of the NutriSelect® Plus line, this medium is manufactured under strict quality controls to ensure high sensitivity and batch-to-batch consistency.
Advantages
- High Sensitivity: Bromocresol purple provides a sharper and clearer color change compared to neutral red, especially in samples with inherent turbidity.
- Effective Selectivity: High-quality ox bile ensures robust inhibition of Gram-positive bacteria and non-enteric flora.
- Standardized Testing: Widely used for the Most Probable Number (MPN) technique for coliform enumeration in water and dairy.
- NutriSelect® Plus Quality: Premium-grade ingredients ensure optimal growth and reliable biochemical reactions.
- Clear Results: The distinct purple-to-yellow transition simplifies the interpretation of presumptive positive results.
Interpretation of Results
| Reaction |
Appearance |
Interpretation |
| Acid Production |
Medium turns yellow |
Lactose fermentation positive |
| Gas Production |
Bubble in Durham tube |
Gas production positive |
| Negative Result |
Medium remains purple |
No lactose fermentation |
Technical specifications
| Catalogue number |
16377 |
| Brand / Product Line |
Sigma-Aldrich / NutriSelect® Plus |
| Target Organisms |
Coliforms (e.g., E. coli, Klebsiella) |
| Typical Composition (g/L) |
Peptone (20.0); Lactose (10.0); Ox bile (5.0); NaCl (5.0); Bromocresol purple (0.01) |
| pH (at 25 °C) |
7.3 ± 0.2 |
| Preparation |
40.01 g/L |
| Storage Temperature |
15 – 25 °C |
Available packaging options
| 16377-500G |
500 g plastic bottle |
