Implen OD600
®
User Manual Version 1.0
21
McFarland
Method Overview
The McFarland standard is a technique used to estimate the density of bacterial suspensions by visual comparison
with a series of turbidity standards. This method is particularly useful when direct cell counting is not feasible or
practical. The McFarland standard is commonly employed in microbiology laboratories for various applications such
as antimicrobial susceptibility testing and bacterial inoculum preparation.
The procedure involves preparing a series of standard turbidity solutions known as McFarland standards. These
standards have specific turbidity levels corresponding to different optical densities. The most common McFarland
standard is 0.5, which is roughly equivalent to 1.5 x 10^8 colony-forming units (CFU) per milliliter for most bacterial
species.
A sample suspension is compared to the standard curve established using McFarland standard solutions with known
turbidity values. This provides an estimate of the cell density in the suspension.
A calibration curve for the 16mm test tube is saved on the device as a standard and can be used as the default
setting.
Note: The default 16mm tube calibration curve was generated using the McFarland standards set from Company ProLab,
Serial Number 395123, traceable to 260-140 SD2350, with a calibration date of February 27, 2024.
Note: Please be aware that standards can vary between batches and supplier. For optimal accuracy, it is recommended to
create your own calibration curve using your own standards, as these can differ and may expire over time.
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