ADHESION OF COAGULASE-NEGATIVE STAPHYLOCOCCI GROUPED ACCORDING TO PHYSICOCHEMICAL SURFACE-PROPERTIES

Physico-chemical cell surface properties of 23 coagulase-negative stap hylococcal strains, including contact angles, zeta potentials and elem ental cell surface composition were measured, together with the adhesi on of all strains to hexadecane, The data were employed in a hierarchi cal cluster analysis, revealing that the 23 strains comprised essentia lly four different groups. Groups I-III were somewhat similar to each other, but group IV was markedly distinguished from the other strains, predominantly through an elevated acidity of the cell surface. These group distinctions were not related to the presence of a capsule or sl ime on the strains. Adhesion of the strains to hexadecane depended cri tically on electrostatic interactions between the hexadecane and the s taphylococci, and adhesion only occurred when the electrostatic repuls ion between hexadecane and the micro-organisms was less than 500 kT at closest approach. Adhesion of six representative strains from all fou r groups in a parallel plate flow chamber to silicone rubber, an impla nt material with similar hydrophobicity to hexadecane, did not show su ch a critical dependence, nor did it relate with the group distinction . Possibly, microbial adhesion to substratum surfaces like silicone ru bber is more complicated than adhesion to an ideally smooth and homoge neous hexadecane surface in an aqueous solution. Adhesion of all six s trains to silicone rubber with an adsorbed conditioning film of plasma proteins was less than that to bare silicone rubber: initial depositi on rates dropped from 2000-3000 cm(-2) s(-1) to 100-300 cm(-2) s(-1) a fter adsorption of plasma proteins, while the stationary end-point adh esion decreased from 10 x 10(6)-15 x 10(6) cm(-2) to 1 x 10(6)-5 x 10( 6) cm(-2). The adhering staphylococci poorly withstood the passage of an air-bubble through the parallel plate flow chamber, regardless of t he presence of a conditioning film, indicating a row affinity of these relatively hydrophilic strains for hydrophobic substratum surfaces.