Identification of Enteric Bacilli Directly from Primary Isolation Media Using Reagent-impregnated Paper Strips

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Abstract
A new and rapid method for the identification of enteric bacilli directly from Hektoen enteric agar plates is described. This procedure is based on the use of reagent-impregnated paper strips and requires only 4 to 6 hr. to obtain data from 13 biochemical reactions. Six to 20 well isolated colonies which are morphologically similar are required for this procedure. Nine hundred forty-three clinical specimens were examined both by the direct method from Hektoen enteric agar and by the conventional method of selecting representative colonies from either eosin-methylene blue or Salmonella- Shigella agars, inoculating a triple sugar iron agar tube, and then carrying out biochemical testing. A total of 1,037 organisms was isolated and correctly identified by the direct method and 1,046 by conventional methods. Each biochemical test carried out with paper strips was controlled by standard media, with a 99.3% correlation between results. Of the 943 clinical specimens examined, 842 (89%) were acceptable for the direct method. The remaining 101 either had too few colonies present or were improperly streaked. The average time required to obtain significant biochemical data by the direct method was 5 hr. after isolation on the Hektoen enteric agar plates, while the average time needed to obtain the same biochemical data using conventional methods was 48 hr. There was less than a 0.05% failure of the direct identification system to allow either isolation or identification, compared with conventional systems described in the literature.4

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