Use of droplet plating method and cystine-lactose-lactng electrolyte-deficient medium in routine quantitative urine culturing procedure

Abstract

Droplet plating of 0.01 ml of 10(-2) dilutions of mixed sonically treated urines onto cystine-lactose electrolyte-deficient agar permits formation of discrete, easily counted colonies within a small circumscribed area without interference by Proteus overswarm. Each colony is considered as arising from a single viable cell. The single dilution permits precise reproducible quantitation of urine bacteria population within the range 10(4) to 10(6) cells/ml of sample. Droplet-plated counts were found to be consistently (approximately) double those determined by standard pour plate quantitation. The method requires only inexpensive readily available materials and has been performed routinely in a large-volume clinical laboratory for several years.