A bacterial co-culture of E. fecalis, S. aureus and E. coli was prepared by diluting the heat-killed bacteria in 1:100 ratio in PBS (pH 7.4, Apoteket, Linköping, Sweden), and in vitro specific anti-E. fecalis antibodies were diluted 1:200 in PBS. The bacteria were incubated overnight with anti- E. fecalis antibodies at 4 °C. Samples were then incubated with nano gold-anti-human IgG antibodies (Nanoprobes, New York, USA) diluted 1:10 in PBS for 2 h. The specimen was mounted on the formvar coated copper grids and counter stained with 2 % Osmium tetroxide (Sigma-Aldrich, Sweden) and were analyzed using TEM1230 Gantan Electron microscope (Linköping University, Sweden).