HIGH-RESOLUTION VISUALIZATION BY FIELD-EMISSION SCANNING ELECTRON-MICROSCOPY OF ENTEROCOCCUS-FAECALIS SURFACE-PROTEINS ENCODED BY THE PHEROMONE-INDUCIBLE CONJUGATIVE PLASMID PCF10

Enterococcus faecalis can acquire antibiotic resistance and virulence genes by transfer of pheromone-inducible conjugative plasmids such as pCF10, which encodes tetracycline resistance. Two pCF10-encoded cell s urface proteins, Sec10 and Asc10, have been previously shown to play a n important role in the transfer of this plasmid. We used high-resolut ion, field emission scanning electron microscopy to visualize these pr oteins on the surfaces of a series of isogenic strains of E. faecalis. Immunogold labeling, using both 6- and 12-nm colloidal gold, unambigu ously demonstrated the expression and distribution of Sec10 and Asc10 on the surface of the E. faecalis cells. On unlabeled E. faecalis cell s which expressed either Sec10 or Asc10, the former appeared to be mor e readily detected. Immunogold labeling of E. faecalis cells expressin g both Asc10 and Sec10 clearly demonstrated the abundance and intermix ing of both proteins on the cell surface except at septal regions. Sec 10 was observed to be distributed over the cell surface. At regions of cell-cell contact, fine strands representing Asc10 were observed dire ctly attaching adjacent cells to one another.