A staphylococcal aggressin

Cell walls from “mouse-virulent” strains of Staphylococcus aureus were found to have “aggressin” activity; the addition of isolated cell walls to a dose of staphylococci that was too low to produce any lesion on subcutaneous injection alone led to the formation of a large necro-purulent lesion. Cell walls from “mouse non-virulent” strains did not enhance lesion production in this way. A method of isolating the lesion-enhancing material from the cell walls of mouse-virulent strains is described. This material consists mainly of mucopeptide with some protein but no teichoic acid. It is resistant to heating at 100°C for 10 min., to tryptic digestion, and to treatment with periodate or formaldehyde, but is rendered soluble and subsequently destroyed by lysozyme.

The lesion-enhancing material, when injected subcutaneously into mice on a plug of cotton dust, inhibits the accumulation of oedema fluid at the site of injection. The corresponding cell-wall fraction isolated from mouse non-virulent strains not only failed to inhibit but even stimulated the exudation of oedema fluid.