Diagnostic Laboratory Section

PREPARATION OF INOCULUM

Mc Farland opacity solution

• Solution A (0.048 M Bacl2)

                        Dissolve 1.75 gm BaCl₂ in 100 ml distilled water

• Solution B (0.36N H₂SO₄)

                       Dissolve 1 ml H₂SO₄ (AG SP gr. 1.84) in 100 ml distilled water

Working solution

• Mix 0.5 ml solution A and 99.5 ml solution B
• Shake vigorously and dispense in to 4-6 ml sealed tubes/ screw capped vials.
• Store in the dark at room temperature and replace after three months

Preparing inoculum

• Select the colonies of uniform morphological character (usually 4-5 colonies) from non specific agar plates (nutrient agar plate) inoculate in soya bean casein digest broth or tryptone soya broth.
• Incubate 2-8 hours and adjust the turbidity of the test suspension (bacterial culture) with sterile broth or saline and compare with the turbidity of the standard (0.5 Mc Farland opacity) against white background with contrasting with black lines until both are equal.