Measuring of Mycobacterium tuberculosis growth. A correlation of the optical measurements with colony forming units

The quantification of colony forming units (cfu), turbidity, and optical density at 600 nm (OD600) measurements were used to evaluate Mycobacterium tuberculosis growth. Turbidity and OD600 mea-surements displayed similar growth curves, while cfu quantification showed a continuous growth curve. We determined the cfu equivalents to McFarland and OD600 units. Key words: bacterial growth, colony forming units, McFarland, Mycobacterium tuberculosis, opti-cal density. The McFarland standards are a series of references of different densities used to estimate the concentration of cells in microbial cultures (Versalovic et al., 2011). The turbidity of these standards is compared to a defined num-ber of Escherichia coli microorganisms per mL (Perilla et al., 2003), and frequently has been used to estimate the den-sity of Mycobacterium tuberculosis cultures (Bergmann et al., 2000; Bollela et al., 1999; Elbir et al., 2008; Leonard e