[Determination of the number of pathogens in bacterial suspensions using laser nephelometry in comparison to the photometry and plate counting method].

Abstract

We determined the number of bacteria in suspensions of three bacterial species (S. aureus ATCC 25923, E. coli ATCC 25922, P. aeruginosa ATCC 27853) in liquid medium using two optical methods - laser-nephelometry and photometry. These results were compared with the CFU/ml determined by the agar plate test in each suspension. Further we defined the applicable range of measurement of both optical methods. The calculated factor of correlation (r = 0.99) attested the very good conformity of the results obtained by both optical methods. The determination of the number of bacteria in suspensions by laser-nephelometry is a simple though very sensitive method. The results can well be reproduced. A further advantage of this method is the immediate information about the number of bacteria in suspension. All these facts recommend laser-nephelometry as a method useful in any bacteriological routine laboratory for determination of the number of bacteria in suspensions.