Biomaterial-centered infections of orthopedic percutaneous implants are serious complications which can ultimately lead to osteomyelitis, with devastating effects on bone and surrounding tissues, especially since the biofilm mode of growth offers protection against antibiotics and since removal frequently is the only ultimate solution. Recently, it was demonstrated that as a possible pathway to prevent infections of percutaneous stainless steel implants, electric currents of 60 to 100 A were effective at stimulating the detachment of initially adhering staphylococci from surgical stainless steel. However, initially adhering bacteria are known to adhere more reversibly than bacteria growing in the later stages of biofilm formation. Hence, the aim of this study was to examine whether a growing Staphylococcus epidermidis biofilm can be stimulated to detach from surgical stainless steel by the use of electric currents. In separate experiments, four currents, i.e., 60 and 100 A of direct current (DC) and 60 and 100 A of block current (50% duty cycle, 1 Hz), were applied for 360 min to stimulate the detachment of an S. epidermidis biofilm that had grown for 200 min. A 100-A DC yielded 78% detachment, whereas a 100-A block current under the same experimental conditions yielded only 31% detachment. The same trend was found for 60 A, with 37% detachment for a DC and 24% for a block current. Bacteria remaining on the surface after the current application were less viable than they were prior to the current application, as demonstrated by confocal laser scanning microscopy. In conclusion, these results suggest that DCs are preferred for curing infections.

In this study, the role of extracellular polymeric substances (EPS) in the initial adhesion of EPS-producing Pseudomonas aeruginosa SG81 and SG81R1, a non-EPS-producing strain, to substrata with different hydrophobicity was investigated. The release of EPS by SG81 was concurrent with a decrease in surface tension of a bacterial suspension from 70 to 45 mJ m N2 that was absent for SG81R1. Both strains adhered faster and in higher numbers to a hydrophilic than to a hydrophobic substratum, but the initial deposition rates and numbers of adhering bacteria in a stationary-end point were highest for the non-EPS-producing strain SG81R1, regardless of substratum hydrophobicity. Both strains adhered less to substrata pre-coated with isolated EPS of strain SG81. Furthermore, it was investigated whether bacteria, detached by passing air-bubbles, had left behind ' footprints ' with an influence on adhesion of newly redepositing bacteria. Redeposition on glass was highest for non-EPSproducing SG81R1 and decreased linearly with the number of times these cycles of detachment and deposition were repeated to become similar to the redeposition of SG81 after six cycles. This indicates that P. aeruginosa SG81 leaves the substratum surface nearly completely covered with EPS after detachment, while SG81R1 releases only minor amounts of surface active EPS, completely covering the substratum after repeated cycles of detachment and adhesion. Atomic force microscopy showed a thick and irregular EPS layer (up to 32 nm) after the first detachment cycle of EPS-producing strain SG81, whereas the putatively non-EPS-producing strain SG81R1 left a 9 nm thin layer after one cycle. X-ray photoelectron spectroscopy indicated that the bacterial footprints consisted of uronic acids, the prevalence of which increased with the number of detachment and deposition cycles.

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