What is McFarland Turbidity?

McFarland turbidity standards are a set of reference solutions used to quantify the turbidity of microbial suspensions, particularly in laboratories. These standards consist of a series of dilutions of barium sulfate or sulfuric acid that produce a range of turbidity levels, typically measured in a nephelometer. The most commonly used standard is the 0.5 McFarland standard, which corresponds to approximately 1.5 x 10^8 bacterial cells per milliliter, making it a useful tool for standardizing bacterial inoculum concentrations in microbiological testing.