Optimal surgical therapy (debridement in chronic osteomyelitis; device exchange in patients with chronic prosthetic joint infection (PJI)) could be sometimes non-feasible, especially in the elderly population. Therefore, a medical therapy with oral prolonged suppressive antibiotic therapy (PSAT) seems to be an option to prevent recurrence and prosthesis loosening. Unfortunately, some patients are infected with resistant pathogens for which oral antibiotics are not suitable. Subcutaneous (SC) administration of injectable intravenous antibiotics as prolonged suppressive antibiotic therapy could be a convenient way to limit catheter-related complications and facilitate ambulatory care. However, there are few data concerning the development of resistance under subcutaneous prolonged treatment with betalactamine. The aim of this study is just to constitute a biological collection from samples from the Gut microbiota in patients having a bone or joint infection treated by a suppressive subcutaneous antibiotherapy with betalactamine. Later analysis will be led on those samples to detect the acquisition of resistance or not.