The antimicrobial effects of HAp and Ag-HAp was observed using periprosthetic infection bacteria such as Pseudomonas Aeruginosa, Staphylococcus Epidermidis, Escherichia coli (DH5$alpha$). Ag-HAp showed good antimicrobial effects. TEM study of E. coli with and without Ag treatment in HAp was experimented in order to find the mechanism of Ag in antimicrobial effects. It was observed that the shape of Ag-treated E. coli was changed, the cells walls became inhomogeneous. The vaculoes at cytoplasm formed into E. coli and finally it was discovered by EDAX that there were many dark granules which contain the Ag element inside the cells.