The aim of this project was to determine the possible role of the extracellular polymeric substances (EPS) of <I>Staphylococcus epidermidis</I> in biomaterial-centered infections. The first part of the project involved the production, isolation, and characterisation of <I>S.epidermidis</I> EPS. A novel method for the isolation of EPS from complex medium was developed which was able to eliminate the problems associated with contamination of bacterial EPS by medium components. Using this method, samples of EPS were obtained from <I>S.epidermidis</I> ATCC 35984 and clinical isolates. In the second part of the project, studies were carried out in order to determine the effect of EPS-eradicating treatments on (a) the susceptibility of stationary phase planktonic cultures to antibiotics, and (b) the integrity of intact biofilms. Eradication of EPS was achieved by exposure of planktonic stationary phase cultures of a clarithromycin-resistant strain of <I>S.epidermidis</I> (Clar^r No.6) to clarithromycin^*. This antibiotic had no effect on the growth or viability of this strain, however, exposure to clarithromycin resulted in a dose-dependent reduction in the dry weight of EPS obtained (5 μg ml^-1 = 50% reduction, 10 μg ml^-1 = 65% reduction). This result was also achieved with stationary phase cultures of a clarithromycin-sensitive strain of <I>S.epidermidis</I> (16595A). The effect of clarithromycin exposure (EPS eradication) on the subsequent efficacies of the antibiotics teicoplanin, cefuroxime and ciprofloxacin, towards stationary phase planktonic cultures of <I>S.epidermidis</I> Clar^r No.6 was determined by total and viable cell counts. No effect on cell viability was observed for combinations of clarithromycin and teicoplanin or ciprofloxacin. However, the 2 to 3 log reduction in viability that was observed for combinations of clarithromycin and cefuroxime suggested that these two antibiotics may have been working in synergy. ^* Clarithromycin is a macrolide antibiotic which is thought to act on the 50 S ribosomal subunit of bacteria which will then interfere with protein synthesis and in turn lead to inhibition of bacterial growth.

The present thesis investigates the friction properties of total knee replacement components using lubricating fluids of different composition and rheology. The first stage of the thesis involves characterization of the rheological properties of hyaluronic acid (HA)/bovine calf serum (BCS) solutions. With increased concentration and molecular weight of HA, higher viscosities and more pronounced shear thinning in steady shear flow was observed. In dynamic oscillatory flow, the elastic character of the solutions became more pronounced and the cross-over frequency decreased upon increasing concentration and molecular weight of HA. The second part of the thesis involves the determination of a method by which the coefficient of friction is estimated using a linear reciprocating wear testing machine with spherical metal indenters articulating on flat UHMWPE samples and deionised (D.I.) water lubrication. A characteristic periodic pattern in the friction behaviour was observed and the coefficient of friction was computed by calculating the average of 30 points about the midpoint between reversals and using the average of three cycles. The third part of the thesis involves the investigation of the effect of fluid composition on the coefficient of friction in knee replacement components. With increased concentration of HA in solution (0-1mg/mL), the coefficient of friction of HA/BCS solutions decreased. However, with HA/BCS solutions of higher HA concentrations (above 1mg/mL), no significant difference in the coefficient of friction was observed. Similar behavior was observed with HA/Albumin solutions. With HA/ D.I. water solutions, the coefficient of friction was almost identical irrespective of the concentration of HA in solution. Significant difference in the rheological properties of HA/D.I. water solutions did not affect the coefficient of friction. The Stribeck analysis revealed that the coefficient of friction with HA/BCS and HA/D.I. water lubrication was not governed by hydrodynamic conditions. The fourth part of this thesis involved characterization of lubricating fluids before and after friction testing. Absorbance and dynamic light scattering measurements of HA/BCS solutions and of HA/Albumin solutions indicate a rise in turbidity and the presence of larger size particles in these solutions after friction testing. The ninhydrin test confirmed the presence of protein in the precipitates obtained following testing. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-09-24 14:06:41.437