Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 48 5 2010 10 15 320 325 EN Norakhoda Sadeghifard Department of Microbiology, School of Medicine, Ilam University of Medical Sciences, Ilam, Iran. Mohammad Hossein Salari Department of Pathobiology, School of Public Health and Institute of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Raza Ghassemi Department of Pathobiology, School of Public Health and Institute of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Saeed Eshraghi Department of Pathobiology, School of Public Health and Institute of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Farzaneh Amin Harati Department of Pathobiology, School of Public Health and Institute of Public Health, Tehran University of Medical Sciences, Tehran, Iran. 2015 09 28 Clostridium difficile is the most common cause of nosocomial diarrhea. It is usually a consequence of antibiotic treatment, But sporadic cases can occur. This study was aimed to determine the frequency of the nosocomial Clostridium difficile (C. difficile) associated diarrhea in Tehran University of Medical Sciences hospitals and study of antibacterial susceptibility of isolates. In this study a total of 942 stool samples from patients with nosocomial diarrhea that were hospitalized in Imam Khomeini hospital, Shariati hospital and Children clinical center were collected. The samples were cultured on a selective cycloserine cefoxitin fructose agar (CCFA) and incubated in anaerobic conditions, at 37°C for 5 days. Isolates were characterized to species level by conventional biochemical tests. Bacterial cytotoxicity was assayed on tissue culture (vero). Antimicrobial sensitivity of isolated toxigenic C. difficile were investigated by kirby Beuer method (disk diffusion). Our findings show that, of the total patients, 57 toxigenic C. difficile (6.1%) were isolated. Results of statistical analysis show significant differences between the rate of isolated toxigenic C. difficile and age group of patients (P<0.05). Among the wards of selected hospitals, in gastroenterology of Children clinical center, Toxigenic C. difficile was isolated from patients most frequently. The sensitivity of isolates to vancomycin, Chloramphenicol and ceftriaxone were higher than other antibiotics. Toxigenic C. difficile is a common hospital-acquired infection. The organism was found in 6.1% hospitalized patients. Further studies to evaluate the rate and role of toxigenic C. difficile in nosocomial diarrheal processes, ecological and pathogenic terms are suggested. https://acta.tums.ac.ir/index.php/acta/article/view/4057 https://acta.tums.ac.ir/index.php/acta/article/download/4057/4032