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Appl Environ Microbiol. 1970 June; 19(6): 911-914
Copyright © 1970 American Society for Microbiology. All Rights Reserved.

Relationship Between Staphylococcal Antiserum Titer and Zone Development on Immune Serum Plates ¹

Food Research Institute, University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

A workable relationship was established between the standard serum titers of staphylococcal immune antisera and the development of precipitin zones on serum agar around colonies of staphylococcal strains producing homologous antigens (enterotoxins). The standard titer of a serum is defined as the reciprocal of that serum dilution which, with 10 µg of pure enterotoxin per ml, will give a precipitin zone 10 mm in length in single gel-diffusion tubes after 7 days of incubation at 25 C. A numerical scale was set up for determining the intensity of precipitin zones on serum agar. A reading of 3 was considered optimum. This correlated well with a standard serum titer of 25, when 1 ml of such a serum was used per 20 ml of medium per serum plate. From this relationship, the minimum volume of serum required to give optimum precipitin zone development can be calculated.

¹ Published with the approval of the Director of the Research Division, College of Agricultural and Life Sciences, The University of Wisconsin.