A COMPARATIVE-STUDY OF DIFFERENT METHODS TO DETERMINE THE TOTAL NUMBER AND THE SURVIVAL RATIO OF BACTERIA IN AEROBIOLOGICAL SAMPLES

Estimation of the total number of microorganisms in an aerobiological sample is dependent on the handling of the sample and the analytical m ethod utilised. In this study different microscopic methods and Coulte r Counter analysis were compared. Preparation of samples for microscop y was found to be critical and the precision within samples varied con siderably depending on the dilution. Improved sample handling resulted in increased precision for all the methods compared. The results show ed that estimations by Coulter Counter were preferred because of its r apidity, high precision and yield. With improved sample handling and b y comparing numbers of viable bacteria by plate count and of total bac teria by Coulter Counter assay, it was possible to determine the survi val ratio for Escherichia coli with a coefficient of variation between samples of 13%. In addition, the use of Coulter Counter avoided under estimation of the total number which can lead to survival ratios large r than 100%. (C) 1997 Elsevier Science Ltd.