Protein A in Staphylococcus aureus isolates from pigs

The presence and quantity of protein A in Staphylococcus aureus 147 isolates from the tonsils of healthy pigs were examined by three methods. Cell-bound protein A was detected in 71 (48%), 104 (71%) and 123 (84%) of 147 isolates by the slide hemagglutination test, microplate hemagglutination test and enzyme-linked immunosorbent assay (ELISA), respectively. Extracellular protein A was not detected in any isolates by the microplate hemagglutination test. When the quantity of cell-bound protein A in the isolates was determined by the ELISA, most of the isolates contained about 0.8 to 2.2 micrograms of protein A/ml in bacterial cell suspensions of a concentration of MacFarland No. 3.