SUMMARY. Investigation was made of the role of protein A and clumping factor in the adhesion of Staphylococcus aureus to the silicone polymer used for manufacture of cerebrospinal fluid shunting systems. The two proteins were judged to contribute non-specifically to adhesion. S. aureus was also shown to be capable of hydrophobic binding, but this was found to be distinct from the demonstrated protein-mediated adhesion.
INTRODUCTIONAs is the case with other surgically implanted materials, the useful life of cerebrospinal fluid (CSF) shunting systems is often limited by infection of the device. Staphylococci are the bacteria most commonly responsible for these infections. Staphylococcus epidermidis has been responsible for > 50% of reported CSF shunt infections. Several workers have studied the mechanisms whereby this otherwise rarely pathogenic micro-organism is able to colonise synthetic materials; carbohydrate-based and protease-sensitive mechanisms of adhesion have been noted, and the role of hydrophobic binding has also been investigated (Christensen et aZ., 1982; Hogt et aZ., 1983). S. aureus has been reported from a smaller number of CSF shunt infections (c. 20%) and, perhaps in consequence, its adhesive mechanisms have received less attention. The observation of a trypsin-sensitive mode of attachment to CSF shunt polymer (Barrett, 1983) prompted the present investigation of the adhesive role of two specific S. aureus surface proteins (protein A and clumping factor). The ability of S. aureus to undergo hydrophobic attachment was also studied.
MATERIALS AND METHODSSubstrates. The substrate for adhesion was polydimethyl and methylvinyl-siloxane (CleanGrade Elastomer MDX4-45 15, Dow Corning, Barry, South Glamorgan). To provide a sufficient surface area for adhesion measurement, this was reduced from the tubular form used for CSF shunts by crushing in liquid nitrogen.The ability to undergo hydrophobic interactions was assessed with Agarose beads either in the native state, or bearing octyl, decyl, or phenyl hydrocarbon groups (Sepharose, Pharmacia Limited, Milton Keynes, Northants).Adhesion measurement. Bacteria used in these experiments were grown on nutrient agar