A Modified Spread Plate Technique for the Determinations of Concentrations of Viable Heterotrophic Bacteria

Abstract

Four techniques for the enumeration of viable heterotrophic bacteria were evaluated for use with environmental samples. Factors being sought were an economical use of materials and time and a superior level of bacterial recovery. The techniques compared in this study were pour plate, spread plate, membrane filtration, and the modified spread plate technique (spot plate). Eighty-four water and thirty-two sediment samples were analyzed for heterotrophic bacterial concentrations using the four methods under study. A statistical analysis of the data by a factorial analysis of variance and a t test indicated that there was no significant difference in the recoveries of the spread plate and spot plate techniques. Both of these produced superior recoveries to the membrane filter and pour plate methods. Poorest recoveries were obtained with the pour plate for water and membrane filter for sediment. The spot plate method was determined to be the most appropriate method for our purposes, since it was superior in most areas of interest to the other methods tested.