Using recombinant Chlamydia trachomatis OMP2 as antigen in diagnostic ELISA test

Abstract

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, Toxoplasma 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%, respectively. Though the sensitivity was higher than results of Euroimmun commercial kit, its specificity was calculated lower than reference kit.

Keywords: Chlamydia trachomatis; ELISA; OMP2.

Fig. 1

Evaluation of cross-reactivity between C. trachomatis rOMP2 and sera of other infectious disease. 1 to 5 hydatid cyst, 6 to 10 Hepatitis C virus, 11 to 15 Hepatitis B virus, 16 to 20 Helicobacter pylori, 21 to 25 Toxoplasma gondii, 26 to 28, Mycoplasma spp., 29 to 31 Cytomegalovirus, 32 to 34 Measles, 35 to 36 Epstein barr virus 37 Varicella zoster virus, 38 to 48 healthy serum samples.

Fig. 2

Comparison of Cut off based on 1/200 and 1/400 serum dilutions. The best Cut off was obtained at 1/200 serum dilution.

Fig. 3

Comparison of sera dilutions with 3mg/mL and 2mg/mL of rOMP2 protein.

Fig. 4

The OD of sera of C. trachomatis suspected patients in rOMP2 coated ELISA plate wells.

Fig. 5

The sera OD for C. trachomatis suspected patients in Euroimmun commercial ELISA kit Since the P-Value = 0.88 is greater than the significance level of a = 0.05, so there is no significant relationship between the rOMP2 and Euroimmun commercial ELISA kit.