ESTIMATION OF VIRULENCE OF STAPHYLOCOCCUS AUREUS FOR MICE: THE EXCEPTIONAL VIRULENCE OF THE SMITH STRAIN

Abstract

A precise method of assaying virulence of Staphylococcus aureus for mice by intraperitoneal injection with mucin is described; the results indicated that most bacteriophage types of S. aureus possessed similar virulence, an LD50 consisting of millions of organisms. The variability in results of similar tests by previous authors is thought to reside in the use of techniques allowing excessive variability.The Smith strain of S. aureus is shown to be exceptionally virulent, requiring only one colony-forming unit to kill a mouse. However, the survival time of mice after inoculation with the Smith strain is longer than that of other strains giving equivalent mortality. An explanation is suggested for this latter phenomenon, and the manner in which the Smith strain causes death is considered.