OXOID MacConkey Agar No. 3

OXOID MacConkey Agar No. 3 – Selective & Differential Medium for Enteric Bacteria

OXOID MacConkey Agar No. 3 is a high-performance selective and differential culture medium designed for the isolation and differentiation of Gram-negative enteric bacteria. Manufactured by Oxoid, this formulation is widely used in clinical, food, water, and pharmaceutical laboratories for reliable detection of lactose-fermenting organisms.

 What is MacConkey Agar No. 3?

MacConkey Agar No. 3 is a refined version of the traditional MacConkey medium with improved selectivity and differentiation. It contains bile salts and crystal violet to inhibit Gram-positive bacteria, allowing selective growth of Gram-negative organisms, especially members of the Enterobacteriaceae family.

 Key Features

• Selective Medium – Inhibits Gram-positive bacteria
• Differential Medium – Distinguishes lactose fermenters from non-fermenters
• Enhanced Performance – Improved clarity and colony differentiation
• Reliable Results – Ideal for routine diagnostic and quality control use

 Composition (Typical per Liter)

• Peptone: 20.0 g
• Lactose: 10.0 g
• Bile salts No. 3: 1.5 g
• Sodium chloride: 5.0 g
• Neutral red (pH indicator): 0.03 g
• Crystal violet: 0.001 g
• Agar: 13.5 g
• Final pH: 7.1 ± 0.2 at 25°C

 Principle of the Medium

• Lactose Fermenters (e.g., E. coli) produce acid → colonies appear pink to red
• Non-Lactose Fermenters (e.g., Salmonella, Shigella) remain colorless or pale
• Bile salts & crystal violet suppress Gram-positive organisms

 Applications

• Clinical Diagnostics – Isolation of enteric pathogens
• Food & Water Testing – Detection of coliform bacteria
• Pharmaceutical QC – Microbial limit testing
• Environmental Monitoring – Contamination analysis

 Directions for Use

1. Suspend the required amount of powder in distilled water.
2. Heat with agitation to dissolve completely.
3. Sterilize by autoclaving at 121°C for 15 minutes.
4. Cool to 45–50°C and pour into sterile Petri dishes.
5. Allow to solidify and inoculate sample.

 Storage & Shelf Life

• Store at 10–30°C in a dry place
• Protect from light and moisture
• Keep container tightly closed

 Precautions

• For laboratory use only
• Use aseptic techniques
• Do not overheat during preparation (may affect performance)

Why Choose OXOID MacConkey Agar No. 3?

With the trusted quality of Oxoid, this medium ensures accurate differentiation and dependable results, making it a preferred choice for microbiology laboratories worldwide.