Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 6 1 2014 02 15 8 13 EN Mahdieh Javaherian Microbiology Department, Islamic Azad University, Qom, Iran. Zarin Sharifnia Cellular and Molecular Biology Research center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Robabeh Taheripanah Fertility and Infertility Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Mojgan Bandepour Cellular and Molecular Biology Research center, Shahid Beheshti University of Medical Sciences, Tehran, Iran AND Biotechnology Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Mohammad Soleimani Microbiology Department, Islamic Azad University, Qom, Iran. Bahram Kazemi Cellular and Molecular Biology Research center, Shahid Beheshti University of Medical Sciences, Tehran, Iran AND Biotechnology Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 2015 10 16 Background and Objectives: The obligate intracellular bacterium Chlamydia trachomatis causes sexually transmissible diseases in human. Timely and sensitive detection of this pathogen is very important. There are many cross-reactions in bacteriological and serological methods in detection of this type of pathogens. The aim of this study was to achieve a more specific antigen for serological tests. Materials and Methods: Blood samples were taken from 192 women with suspected chlamydial infection and sera were isolated. ELISA plate wells were coated with recombinant C. trachomatis OMP2 as antigen. Cut-off system was determined with 40 negative sera. The final results of this research were compared with Euroimmun commercial kit. Results: The ELISA system cut-off was calculated at 0.27 using negative sera samples. ODs of positive samples were higher than 0.27 and negative samples were lower than it. We obtained 30 samples (15.62%) as positive and 162 cases (84.37%) as negative. Sensitivity and specificity of the recombinant antigen were 90% and 86%, respectively. This antigen showed no cross-reactivity with sera of patients infected with Hydatid cyst, HCV, Epstein barr virus, HBV, Helicobacter pylori, Toxo- plasma gondii, Cytomegalovirus, Mycoplasma, Measles and Varicella zoster virus. Conclusion: The sensitivity and specificity of rOMP2 in ELISA for detection of C. trachomatis were 90% and 86%, respec- tively. Though the sensitivity was higher than results of Euroimmun commercial kit, its specificity was calculated lower than reference kit. https://ijm.tums.ac.ir/index.php/ijm/article/view/474 https://ijm.tums.ac.ir/index.php/ijm/article/download/474/250