A NEW VIRULENCE TEST FOR STAPHYLOCOCCUS AUREUS AND ITS APPLICATION TO ENCAPSULATED STRAINS

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Abstract
An encapsulated variant of Staphylococcus aureus was obtained after laboratory passage in Casamino Acids glycerol broth. Hyperimmune rabbit or rooster serum, prepared by injection of washed, formalin-killed, whole cell vaccines, regularly produced specific capsular reactions* of 4-to 8-hour broth cultures of homologous organisms. Intravenous injection of the encapsulated variant into 12- to 13-day-old embryonated hens' eggs regularly produced death when 1000–2000 organisms were injected. The passive protective properties of hyperimmune serum or human gamma globulin were readily demonstrated if 5–20 LD50 doses of a young broth culture of the encapsulated variant were mixed with the antiserum prior to injection into the eggs. The finding of anticapsular antibodies in samples of human plasma indicated that the capsular antigen or one closely related to it was produced in vivo.

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