Determination of cell number and size of a population of Pseudomonas fluorescens by image analysis

Microscopic observations of a population of Pseudomonas fluorescens were digitised by a frame grabber and an appropriate threshold was chosen to extract the objects from the background. Fully grown, single bacteria were normally distributed around two mean sizes. Two Gauss functions were fitted by least square analysis to these points and the enumeration of single cells was obtained from the area of each Gauss curve and made for each threshold selected. The number of particles counted was constant over a large range of threshold (80-180) whereas the cell area increased with the threshold installed.Junta Nacional de Investigação Científica e Tecnológica (JNICT) - PRAXIS/2/2.1/BIO/37/94