Experimental Staphylococcus Aureus Infections in Humans

S. aureus infections have been consistently induced in normal human skin by applying large inocula to areas degermed with ethanol and kept moist under an occlusive dressing. The ED50 was approximately 103/cm2. With about 106 organisms, cm2, an erythematous rash appeared in three days which evolved to an intense papulo-vesicular eruption, by six days. Removal of the dressing was followed by swift death of almost all the organisms followed by immediate resolution of the lesion within a few days. There was a great loss of viable cells in the first hour after application which continued for 24 hours; thereafter, the organisms proliferated to a peak density of about 2 ×107/cm2. The resident cocci and diphtheroids began to re-enter the site by about the 3rd day and were completely restored by 6 days. The organisms were confined to the surface and did not proliferate within the living portion of the skin. Histopathologically the lesion was a toxic dermatitis with epidermal necrosis, edema, hemorrhange and thrombosis. This clinical entity may be described as toxic pyoderma