The emergence of resistance to fluoroquinolone (FQ) is a major problem worldwide. The commensal flora is the main reservoir for antibiotic resistance. Understanding the factors (environmental, patient-related, dosis-related, drug-related…) involved in the emergence of resistance to fluoroquinolones in the commensal flora of patients treated with a FQ, may help prevent it and preserve the efficiency of these important antibiotics. Samples of rectal, nasal and pharyngeal flora will be collected from hospitalized patients before receiving a FQ, at the end of the treatment and 1 month after the end of treatment. Clinical data will be collected. The incidence and risk-factors associated with the emergence of resistance to FQ will be assessed by comparing groups with and without resistance both at the end of treatment and 1 month later.