Turbidity standards for the preparation of standardized bacterial suspensions.
Polymer microparticle suspension (PMS).

McFarland PMS standards made of polymer microparticles are equivalent turbidity standards to the original McFarland BSS standards.

The optimized Polymer Microparticle Suspension is slower than the barium sulphate variant and has a better durability. The CLSI (Clinical and Laboratory Standards Institute) accepts the use of polymer polystyrene/latex particle suspension turbidity standards for the preparation of standardized bacterial suspensions.

The cell density of a bacterial suspension is adjusted in a simple comparison with the turbidity of the standard. This can be done both in direct visual comparison and by measurement in a spectrophotometer.

The turbidity value of the standard of 0.5 MFU (McFarland Unit) corresponds to a culture density of 1.5 x 108 cells/ml. This cell density is especially required for bacterial inocula for the antibiotic sensitivity test. For further cell concentrations see product information.

* Available as a customised version on request.

References:

• Joseph McFarland, M. D., JAMA, XLIX, 14,1176-1178 (1907).