Mc. Farland Standard

Mc Farland Standards are used for standardization of numbers of bacteria when required by procedures or for susceptibility testing. The basic 0,5 Mc Farland Standard contains approximately 1x10⁷ to 1x10⁸ CFU/ml (1x10¹⁰ to 1x10¹¹ CFU/L)

FORMULA

0,5 Mc Farland Standard
Barium Chloride, 0,048M solution	0,5 ml
Sulfuric Acid, 0,18M solution	99,5 ml
O.D at 625 nm	0,08-0,1
1,0 Mc Farland Standard
Barium Chloride, 0,048M solution	1,0 ml
Sulfuric Acid, 0,18M solution	99,0 ml
O.D. at 625 nm	0,16-0,2
2,0 Mc Farland Standard
Barium Chloride, 0,048M solution	2,0 ml
Sulfuric Acid, 0,18M solution	98,0 ml
O.D. at 625 nm	0,32-0,4
3,0 Mc Farland Standard
Barium Chloride, 0,048M solution	3,0 ml
Sulfuric Acid, 0,18M solution	97,0 ml
O.D. at 625 nm	0,48-0,6
4,0 Mc Farland Standard
Barium Chloride, 0,048M solution	4,0 ml
Sulfuric Acid, 0,18M solution	96,0 ml
O.D. at 625 nm	0,64-0,8
5,0 Mc Farland Standard
Barium Chloride, 0,048M solution	5,0 ml
Sulfuric Acid, 0,18M solution	95,0 ml
O.D. at 625 nm	0,8-1,0

This approximate formula may be adjusted and/or enriched to obtain best results.

STORAGE
Store standards at 2-30º C protected from direct light.

PROCEDURE
Vigourously agitate these turbidity standards on vortex just before use.

1. Inoculate a broth with 4-5 similar colonies from an agar plate culture. Mix thouroughly.
2. Incubate at 35º C for 2-6 hours until it achieves or exceeds the turbidity of Mc Farland Standard required. If necessary, dilute suspension with broth or saline to obtain a turbidity visually comparable to required standard.
3. Following standardized procedures inoculate plates for antimicrobial disk susceptibility tests. For testing the nutritive capacity of a medium dilute cell suspension according to previous references.

REFERENCES

1. Lennette, E.H., Ballows, A., Hausler, W.J.Jr., and Shadomy, H.J. Manual of Clinical Microbiology. 4th ed. 1985 Washington D.C.: American society for Microbiology.
2. NCCLS 1990 Quality assurance for commercially prepared microbiological culture media Approved standard Document M22-A Vol.10, No.14
3. NCCLS 1990 Performance standards for antimicrobial disk susceptibility tests 4th ed. Approved standard Document M2-A4 Vol.10, No.7