Rapid Serological Typing of Shigellae: A Preliminary Note

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Abstract
When a strain is isolated or received for identification it is first tested by spot agglutination in 2 polyvalent sera at 1:10 dilution. The 1st serum contains agglutinins for Shigella paradysenteriae type Flexner I ("V"), Flex-ner II ("W"), and Flexner III ("Z"). The 2d has agglutinins against Flexner IV (Boyd 103), Flexner V (Boyd P. 119), and Flexner VI (Boyd 88-Newcastle types). The organisms agglutinate quickly and completely in the polyvalent serum containing the specific agglutinins of proper type. There is some cross agglutination in these 2 sera owing to the common group antigens of the several components (e.g., Flexner III and Flexner V strains will often cross agglutinate to titer, but the heterologous agglutinins may easily be removed from their sera by cross absorption, without materially reducing the titer for the homologous type). The next step is to type the microorganism by individual tests with the various factors present in the polyvalent serum. For these tests the spot plate is also used and the specific sera are employed at a serum dilution of 1:5 or 1:10. Agglutination is rapid and complete and the strain can usually be tentatively identified by this means alone. For confirmation of the results obtained by spot agglutination, a simple, 1-tube agglutination test has been devised. For these tests the sera, are absorbed, when necessary, and titrated with known strains of the various types. The sera are employed at a dilution which will give rapid and specific agglutination. If the culture being tested is believed to be a Flexner I, for example, it is set up in 1-tube tests against absorbed Flexner I, IIa, IIb, and III antisera; if it is thought to be a Flexner V, it is tested with Flexner IV, V (absorbed with HI), and VI antisera. A control consisting of one tube of saline suspension only is included with each test. The test are then placed in a water bath at 50[degree]-62[degree] C. It is usually possible to read the tests after 2 hrs.; however, some strains (e.g., Flexner IIb) may require 4 hrs. for complete agglutination. The results of such tests with various Flexner types are contained in a table.

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