Purple Broth w/Lactose and Durham Tube 8mL, 10/Pk

Purple Broth with Lactose is a differential medium used to test an organism's ability to ferment the disaccharide Lactose. Like its Dextrose counterpart, this broth uses Bromocresol Purple as the pH indicator, making it particularly useful for identifying Gram-negative enteric bacteria and enterococci.

The Test Principle:

1. Carbohydrate (Lactose): The medium supplies Lactose as the fermentable sugar. Bacteria must possess the enzyme $\beta$-galactosidase to break this down into glucose and galactose for fermentation.

2. pH Indicator (Bromocresol Purple):

   • Purple: Neutral pH (Initial state/Negative).

   • Yellow: Acidic pH (Positive for acid production).

3. Durham Tube: An inverted vial to detect gas production ($CO_2$ and $H_2$).

Clinical Significance (Coliforms):

This test is a classic method for distinguishing Coliforms (Lactose fermenters like E. coli and Enterobacter) from Non-Coliforms (Non-fermenters like Salmonella and Shigella).

• Rapid Fermenters: Organisms like E. coli will typically turn the tube Yellow with gas within 24-48 hours.

• Slow Fermenters: Some organisms (like Serratia or Citrobacter) may take longer to turn the tube yellow.

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