Studies on the pathogenicity of thiamineless dwarf-colony variants of Staphylococcus aureus isolated from the bovine udder.

The pathogenic characteristics of thiamineless dwarf-colony variants of Staphylococcus aureus (D strains) were compared with those of normal S aureus isolated from the bovine udder. Intravenous injection of D strains into embryonated hen's eggs and intracranial inoculations into mice produced similar results to those with normal S aureus. Intramammary infusion of D strains into normal cows resulted in mastitis which was indistinguishable from the type produced by infusion of S aureus. Intramuscular injection of thiamine HCl into cows with chronic mastitis due to D strains did not alter the course of the disease, although normal sized S aureus colonies were isolated several days after thiamine injection.