Determination of protein A in Staphylococcus aureus strains from a collection

The author used the haemagglutination method to estimate A protein in 153 strains of Staphylococcus aureus from collections. Protein A was detected in 66% of coagulase positive strains deposited in the course of time in the collection in 1983-1988. All strains were kept in skimmed milk at -20 degrees C. For evaluation of the reaction a semiquantitative scale was proposed. The author observed a diminished capacity to form protein A with the time of storage of the strains. In strains deposited for a shorter time in the collection (only three years) the percentage of positive results rose to 92.5%. In coagulase negative strains protein A was not detected.