Probiotics and prebiotics - Progress and challenges
Colloids and Surfaces B: Biointerfaces
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Physicochemical surface characteristics of two pairs of coagulase-negative staphylococcal isolates, obtained from the skin of prematurely born children and genetically only differing in plasmid profiles were measured in order to determine a possible association between the plasmid content and their surface characteristics. The isolates Staphylococcus epidermidis 169 and 242 harboured six plasmids of 3.1, 4.4, 8.7, 13.5, 27 and ≈56kb, whereas two other isolates, S. epidermidis HBH2 and HBH276, carried four plasmids of identical molecular size (4.4, 8.7, 13.5 and 27 kb) and one other plasmid of 2.3 kb. The zeta potentials of all isolates in 10 mM potassium phosphate solutions were negative in the pH range 2-9 and their pH dependences were roughly similar. Also contact angles with water, formamide, diiodomethane, α-bromonaphthalene and hexadecane on bacterial lawns were rather similar, albeit that isolates 169 and 242 had slightly higher water contact angles (37° and 30° respectively) than isolates HBH2 and HBH276 (28° and 29° respectively). Adhesion to hexadecane was significantly higher for isolates 169 and 242 carrying the ≈56kb plasmid (60-62%) than for isolates HBH2 and HBH276 (36-49%). Incidentally, it is noted that the isolates most hydrophobic by microbial adhesion to hexadecane (MATH) also had the highest water contact angles. Elemental surface concentration ratios determined by X-ray photoelectron spectroscopy (XPS) on freeze-dried bacteria indicated that isolates carrying the ≈56 kb plasmid had slightly lower N/C (0.116-0.123) and P/C (0.022) ratios compared with the N/C (0.115-0.131) and P/C (0.026-0.039) ratios of the isolates lacking this plasmid. The O/C ratio ranged from 0.493 to 0.595 for all the isolates. Cluster analysis on the basis of the combined data for water contact angles and adhesion to hexadecane yielded a grouping of the strains according to their plasmid profile. It is concluded that the functions encoded by the ≈ 56 kb plasmid may involve modulation of the cell surface "hydrophobicity", which appears to be masked by phosphorus-containing groups, since adhesion to hexadecane related inversely with the P/C surface concentration ratio from XPS. © 1994.