MICROFLORA ON EXPLANTED SILICONE-RUBBER VOICE PROSTHESES - TAXONOMY, HYDROPHOBICITY AND ELECTROPHORETIC MOBILITY

Silicone rubber voice prostheses are implants which are inserted in a non-sterile environment and therefore become quickly colonized by micr o-organisms. The micro-organisms exist on the medical grade silicone r ubber as mixed biofilms of bacteria and yeasts. A total of 79 bacteria l and 39 yeast strains were isolated from these biofilms by soft ultra sonic treatment. Gram-positive/catalase-negative and Gram-positive/cat alase-positive cocci represented the dominant bacterial strains. The y easts were mainly Candida species. Further characterization of cell su rface properties such as hydrophobicity by microbial adhesion to hexad ecane and electrophoretic mobility showed a distinct difference when t he bacterial strains were compared with the yeasts. The bacterial hydr ophobicities ranged from 0 to 100% adhesion to hexadecane, whereas the yeast strains, especially the Candida albicans strains, all had marke dly hydrophilic cell surfaces. A comparison of the electrophoretic mob ilities showed also differences between bacteria and yeast. The values for the bacteria were found to be between -2.5 to -0.5 (10(-8) m(2) V -1 s(-1)), whereas for the yeasts electrophoretic mobilities were more positive. Based on the adhesive properties of the isolated micro-orga nisms, strategies can now be developed to modify the properties of the silicone rubber to reduce biofilm formation on such prostheses.