Use of the gravimetric diluter in microbiological work

Manual dilutions of food samples (e.g., 1:10 dilution) for microbiological investigations are cumbersome. We tested an automatic diluter (Model GD-600 Gravimetric Diluter, Spiral System, Inc., Bethesda, MD) for accuracy and sterility for microbiological work and found that the system provided ±0.1 to +0.2 g of accuracy in delivering a commanded amount of diluent. The delivered diluent was essentially sterile, with a few samples giving 1 to 4 colonies per ml after plating. With this system, weighing and dilution are fast, easy, and accurate.