A NEW METHOD FOR STREAKING BLOOD AGAR PLATES

Abstract

A NEW METHOD for the streaking of agar plates and the obtaining of isolated bacterial colonies on the agar surface is presented. The method involves the use of thin paper discs which are placed on the agar and cover the entire surface. The disc has linear slits of narrow width allowing optimum amounts of the specimen to be distributed through the paper and onto the agar surface when the paper is rubbed with a swab bearing the inoculum. Robert Koch in his epochal publication of 18811,2 introducing the pure culture technique into bacteriology first described the use of solid gelatin media. In this publication he described the use of a platinum wire for the streaking of specimens onto the gelatin surface. Hesse in 1884, while working in Koch's laboratory, discovered the use of agar as a replacement for gelatin.3 Petri,4 in 1887, also working in Koch's laboratory, invented the culture dish which bears his name. It is notable that, with minor exceptions, the technique of streaking specimens onto agar plates by means of a wire loop has remained virtually unchanged to this date. Throat cultures of patients in St. Francis Hospital, Evanston, Illinois; Lutheran General Hospital, Park Ridge; and the University of Illinois Hospital, Chicago, were studied. Studies were also made of throat cultures in the laboratories of the Evanston Board of Health. A total of 550 throat cultures was obtained. Cultures were made m 450 cases using the Iso-Disc technique only, and 100 cultures were studied in duplicate with the Iso-Disc method and the conventional wire loop method.