Simple and effective method for selecting protein A-dificient mutants by consedimentation with sensitized sheep erythrocytes.

An effective slection method for protein A-deficient mutants was devised by means of cosedimentation with sensitized sheep erythrocytes and anti-protein A serum agar plates. Hitherto, two types of mutants have been successfully isolated by this method. One was deficient in both cell-bound protein A and soluble protein A. The other seems to release extracellularly soluble protein A but does not possess cell-bound protein A. Spontaneous mutants of the former type were contained in the culture of Staphylococcus aureus 248betaH in a concentration of approximately 10-minus-5, which is ten times as much as the latter. Repeated cosedimentation procedure greatly increased the efficiency of isolation of the mutants. As a result, a majority of the bacterial cells remaining in the final supernatant after three cosedimentation procedures were of the two mutant types. Details of the method as well as some preliminary results are described.