The Inhibition of the Spreading Growth of Proteus and other Bacteria to Permit the Isolation of Associated Streptococci

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Abstract
Methods for the inhibition of the spreading growth of Proteus and other organisms to allow the isolation of associated streptococci were compared. Alterations in the moisture content of the medium were accomplished by the use of the unglazed porcelain Petri dish cover, increased agar conc. (5%), and excess quantities of NaCl (6%). Although spreading was inhibited by each of these methods, isolation of streptococci was prevented because of desiccation of the medium, renewal of spreading upon the addition of blood, and because of the salt sensitivity of the beta hemolytic streptococci. The latter method proved successful for the isolation of Strep. viridans and the enterococci which are not sensitive to 6% NaCl. The use of specific immune globulin in the medium was sharply limited because of the strain specificity in the Proteus group. The chemical agents employed were lactic acid, alcohol, Na azide and K tellurite. Of these only Na azide and alcohol were effective. The chief disadvantage with alcohol was the complete hemolysis induced in blood agar making primary isolation of streptococci on the basis of hemolytic properties impossible. Na azide (1:5,000) eliminated the spreading of Proteus.