[Improved method for the demonstration of protein A of Staphylococcus aureus (author's transl)].

Protein A (PA) could be extracted completely from Staphylococcus aureus by treatment with concentrated formic acid. This led to the development of a semi-quantitative determination of PA by hemagglutination (fig. 1). The treatment with formic acid yielded PA more effectively than the commonly used extraction by boiling (table 1). It could be conducted directly on a loopfull of staphylococci obtained from blood agar. It required no additional cultivation in a fluid medium. Most suitable for the hemagglutination was a commercial preparation of Rh-positive human erythrocytes, blood group O, loaded with Rh-antibodies from humans. This relatively stable preparation had also a higher susceptibility for PA in the slide-test and served for a better detection of PA-positive staphylococci (table 2).