One of the major drawbacks in the use of biomedical materials is the occurrence of biomaterial-centered infections. After implantation, the host interacts with a biomaterial by forming a conditioning film on its surface and an immune response towards the foreign material. When microorganisms can reach the biomaterial surface they can adhere to it. Adhesion of microorganisms to an implant is mediated by their physico-chemical surface properties and the properties of the biomaterial surface itself. Subsequent surface growth of the microorganisms will lead to a mature biofilm and infection, which is difficult to eradicate by antibiotics.Surface treatment to modify device properties has been used to increase the bio-compatibility and decrease the susceptibility to bacterial adhesion. In this study a total 52 clinical samples were isolated from implant infection. The microorganism were identified by API system .the susceptibility test was carried out for all isolates to detect multidrug resistant isolates and biofilm formation test was carried out to detect positive slime producing isolates . Antimicrobial activity of irradiated Hydroxyapatite (HAp) was carried out against positive slime producing isolates The synergistic interaction between irradiated HAp and some antibiotics was carried out to evaluate the effect of irradiated HAp and antibiotics on microbial growth. The microbial adherence on 316stainless steel chips as biomaterial was detected before and after coating with irradiated HAp and / or antimicrobial agent and it was noticed that the number of adherent strains decreased after coating with irradiated HAp and /or antimicrobial agent.  HAp was exposed to gamma irradiation at doses levels 15 and 25kGy to study the effect of radiation on the antimicrobial activities of HAp. The results revealed that the doses 15 and 25kGy increased this activity but the 25KGy showed higher antimicrobial activity.