Determination of Microbial Load in Water by Dynamic Speckle Pattern Analysis

A preliminary study is presented on the use of Dynamic Laser Speckle for determining microbial concentration in water. Different concentrations of bacteria were placed in physiological solution on a Petri dish. Sterile physiological solution was used as control. Each plate was individually trans-illuminated with an expanded and attenuated HeNe laser (20 mw and 632.8 nm wavelength) from below through a ground glass diffuser. The videos obtained were processed with the slightly modified Temporal Contrast algorithm. Results allow qualitative visualization of the difference in activity produced by the different concentrations of bacteria in water. The difference in speckle activity between samples with and without bacteria gives confirmatory results of microbial presence in water, not being possible yet to differentiate between bacterial concentrations, since the difference in activity values are not significant. Results obtained will allow progress towards the development of a rapid method for microbiological control of water samples, potentially applicable to in situ monitor ing of effluents and watercourses.