Azide Dextrose Broth (ROTHE) - ADB
CAT No: AS‑1128
Selective Enrichment Medium for Enterococci Detection in Water, Food, and Dairy (ISO 7899‑1 Compliant)
 
Overview
Azide Dextrose Broth (ROTHE) is a highly selective liquid enrichment medium developed by Rothe et al. (1954) for the isolation and presumptive detection of faecal streptococci / enterococci (Enterococcus faecalis, E. faecium, E. durans, etc.) from water, milk, foods, and clinical specimens.
The presence of sodium azide (0.02–0.04%) inhibits Gram‑negative bacteria and most Gram‑positive organisms, while enterococci grow rapidly, producing dense turbidity within 18–24 hours at 37 °C. This broth is the official enrichment step in ISO 7899‑1 and DIN 38411 before confirmation on bile‑aesculin‑azide agar or membrane filtration.
 
Applications
Selective enrichment of enterococci from heavily contaminated samples (water, sewage, milk, meat products)
Most Probable Number (MPN) determination of faecal streptococci in water quality testing
First enrichment step in ISO 7899‑1 and national standards for enterococci in bathing and drinking water
Pre‑enrichment before confirmation on Kanamycin‑Aesculin‑Azide Agar or Bile Aesculin Agar
 
Key Features & Benefits
High selectivity due to sodium azide inhibition (0.2–0.3 g/L typical)
Rapid and heavy growth of enterococci (visible turbidity within 18–24 h)
Double‑strength formulation available for MPN tube series
Positive tubes show dense turbidity with sediment, requiring confirmation by subculture
 
Standard Composition (per liter – single strength)
Peptone / Meat Extract – 20.0 g
Glucose (Dextrose) – 5.0 g
Sodium Chloride (NaCl) – 5.0 g
Dipotassium Phosphate (K₂HPO₄) – 2.7 g
Monopotassium phosphate (KH₂PO₄) – 2.7 g
Sodium Azide (NaN₃) – 0.2g 
Final pH: 6.8 ± 0.2 at 25 °C
 
Preparation Instructions
Dissolve 32–35 g dehydrated medium in 1 L purified water.
Heat with frequent agitation until fully dissolved.
Do not autoclave – sodium azide is heat‑labile and toxic.
Dispense into tubes:
Single strength: 10 mL per tube
Double strength: 5 mL per tube (for MPN series)
Sterilize by tyndallization (100 °C for 30 min on three successive days) or by membrane filtration if required.
 
Incubation Conditions
Temperature: 35–37 °C (or 44 °C for faecal streptococci confirmation)
Time: 18–48 hours
Positive reaction: Dense turbidity, often with sediment
 
Storage & Stability
Dehydrated medium: Store at 10–30 °C, dry and protected from light
Prepared broth: Store at 2–8 °C; use within 4 weeks
 
Safety Note
Sodium azide is highly toxic and forms explosive compounds with copper or lead plumbing.
Dispose of broth and tubes properly according to laboratory safety protocols.
 
Intended Use
For laboratory, water, food, and environmental microbiology use only. Not for diagnostic or therapeutic applications without proper validation.