A MICROMETHOD FOR ENUMERATION OF COLONY-FORMING BACTERIA

A method for enumeration of viable bacteria in eutrophic and mesotroph ic habitats based on inoculating small spots on the surface of solid m edia with aliquots from serial dilutions of water samples is suggested . The amount of microorganisms capable of growing on the media used is estimated via two independent approaches: (1) direct count of the num ber of colonies on the area inoculated from a certain dilution and (2) count of growth-yielding inoculated spots with further assessment of the number of bacteria in the sample by the statistical method employi ng the most-probable-number (MPN) tables. The exact procedure involves application onto the surface of a solid medium (according to a defini te pattern) of 3 to 10 separate 1-mu l drops from each of three to fiv e successive tenfold dilutions of the investigated sample. After a sta ndard incubation period, the number of colonies on an area inoculated from a certain dilution and the occurrence of bacterial growth in each inoculation spot are taken into account. The results obtained in the latter case are coded and converted to cells/ml by means of the MPN ta bles. The suggested method allows several-fold reduction of the amount of laboratory glassware and nutrient media used, without any decrease in reliability and information content of the results obtained.