HETEROGENEITY OF CELL-ASSOCIATED CP5 EXPRESSION ON STAPHYLOCOCCUS-AUREUS STRAINS DEMONSTRATED BY FLOW-CYTOMETRY

It was reported previously that two capsular polysaccharides, types 5 and 8 (CP5 and CP8), account for 70 to 80% of Staphylococcus aureus st rains isolated from human and animal sources, The capsular material ha s been shown to play a part in virulence and in resistance to phagocyt osis, With a view to investigating the role that CP plays in pathogeni city or protection, relative measurement of cell-associated CP is desi rable, Flow cytometry, which permits the analysis of individual bacter ia, was used to that end, Thirty isolates expressing CP5, of human (n = 7) and animal (cow, n = 11; goat, n = 3; swine, n = 3; hen, n = 3; a nd rabbit, n = 3) origin, were cultivated on either brain heart infusi on agar (BHI) or modified medium 110 (mod 110) agar, Staphylococci wer e incubated with a mouse anti-CP5 monoclonal antibody (an immunoglobul in M, which does not react with staphylococcal protein A) and then sta ined with a fluorescein-labeled anti-murine antibody, The bacteria wer e washed, sonicated, and analyzed by flow cytometry, Except for three isolates, the expression of cell-bound CP5 was higher when bacteria we re cultivated on mod 110 than when they were cultivated on BHI, We fou nd a wide intraisolate phenotypic heterogeneity in surface-exposed CP5 in many strains, which appeared as mixtures of stained and unstained bacteria, Four main patterns could be distinguished on the basis of th e distribution of the fluorescence of individual bacteria within the s train population as a function of growth medium, Great variations in b oth percentages of stained bacteria and fluorescence intensity were re corded among strains regardless of their origin, Flow cytometry analys is provided information on both the relative amounts and the distribut ion patterns of the surface expression of CP, This information is pote ntially useful for the evaluation of the part played by the capsule in the interaction of bacteria with host cells or for the study of the a ctivities of antibodies to this target antigen, such as opsonization o r prevention of adherence.