The possible role of the extracellular polymeric substances (EPS) of Staphylococcus epidermidis in biomaterial-centered infections
The aim of this project was to determine the possible role of the extracellular polymeric substances (EPS) of Staphylococcus epidermidis in biomaterial-centered infections. The first part of the project involved the production, isolation, and characterisation of S.epidermidis 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 S.epidermidis 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 S.epidermidis (Clarr 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 S.epidermidis (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 S.epidermidis Clarr 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.