Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 13 4 2025 12 12 67 74 Ali Ahmadi Molecular Biology Research Center, Biomedicine Technologies Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran Soghra Khani Department of Biochemistry, Pasteur Institute of Iran, Tehran, Iran Abas Ali Imani Fooladi Molecular Biology Research Center, Biomedicine Technologies Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran 2025 08 25 2025 08 28 Background:   The study aims to identify bacterial agents and study the prevalence of pathogenic bacteria isolated from patients admitted to the Intensive Care Unit, as well as recognize factors affecting nosocomial infection that can lead to control and treatment of these infections. Methods:   This study was conducted in the Intensive Care Unit of Baqiyatallah Hospital in Tehran. Totally 738 samples were obtained from patients with a bacterial infection were included in this study. Patient information, including age, gender, type of clinical sample, susceptibility testing, year of hospitalization in to the Intensive Care Unit, and the prevalence of isolated bacteria, was analyzed. Results:   The findings of this study revealed that Acinetobacter, Pseudomonas aeruginosa, and Staphylococcus aureus had the highest and Escherichia coli, Enterobacter, and Streptococci had the lowest prevalence in the to the Intensive Care Unit isolates. Gram-negative bacteria were responsible for most nosocomial infections in the Intensive Care Unit. The rate of nosocomial infections in the Intensive Care Unit had a constant incidence in the recorded years. The rate of nosocomial infections was higher in the male patients than female, with a higher average year of age. Also, the results showed that most isolates were multiple drug resistant. Conclusion:   The high rate of nosocomial infections in to the Intensive Care Unit belonged to respiratory infections. Factors such as intubation and elderly age are associated with the type of infection. Bacterial isolates had a high level of resistance to most antibiotics. Therefore, periodic antibacterial sensitivity assessment could help optimize empirical antibiotic therapy against to the Intensive Care Unit acquired infections.   https://jmb.tums.ac.ir/index.php/jmb/article/view/607