EVALUATION OF IMAGE-ANALYSIS AND LASER GRANULOMETRY FOR MICROBIAL CELL SIZING

A direct cell size measurement technique and an image analysis based s izing method were developed. The former consisted of a manual size mea surement of the two-dimensional cell images on a video screen, with au tomatic data recording. This method was chosen as the reference. The l atter, a semiautomatic method took advantage of a commercial computer program designed for image processing and particle morphology analysis . It gave average and median size values which were compatible with th e manual method. However, the performance of these time consuming meth ods is limited. Hence, the laser granulometry technique, intrinsically far more powerful while capable of analysing millions of sample objec ts in a short time delay, was applied. The comparison revealed that th is method gives too low size values, particularly in disagreement with the known dimensions of the bacterial (Zymomonas mobilis) cells. A si ze correction method was developed to realign the granulometry results of Z. mobilis cell samples with those of the direct manual measuremen t method.