Explain the Turbidity Measurement?

Presence of sufficient number of microbes makes the liquid medium turbid. Turbidity also increases with the multiplication of microbes. Estimation of turbidity can be used both for the quantitation of microbes and monitoring microbial growth. The technique depends on the fact that cells scatter the light striking them and the amount of scattering is directly proportional to the biomass of cells present and indirectly to the cell number. The scattering of light can be measured by spectrophotometer or photometer. In the instrument, a beam of light is passed through a cell suspension and the amount of unscattered light is detected by a light sensitive detector. Photometer uses a simple filter to generate incident light whereas in spectrophotometer, prism is used instead of a filter. Commonly used wavelengths for bacteria are 540 nm, 600 nm and 660 nm. More the number of microbes in the suspension, less is the light reaching to the detector and read as percent transmission or absorbance (OD, optical density, a logarithmic expression).