Comparative diagnostic evaluation of OMP31 gene based TaqManA (R) real-time PCR assay with visual LAMP assay and indirect ELISA for caprine brucellosis

摘要

Brucellosis is one of the leading causes of abortion in domestic animals that imposes costs on both economy and society. The disease is highly zoonotic and poses risk to animal handlers due to its zoonotic nature. It causes stillbirth, loss of kids and abortion in last term of pregnancy. Reproductive damage includes infertility in does and orchitis and epididymitis in breeding bucks, which result in high financial losses to farmers and the agriculture industry as a whole. It requires highly sensitive and specific assays to diagnose the disease at field level. In the current study, a visual loop-mediated isothermal amplification (LAMP) assay and the TaqManA (R) real-time PCR were developed with high sensitivity and specificity. For the TaqManA (R) probe, real-time PCR primers were developed using Omp31 gene as target and primers were designed using discontiguous conserved sequences of Omp31 gene. The Omp31 probes were designed by attaching 6-FAM reporter dye at the 5' end and BHQ-1 quencher at the 3' end. Published primers were used for visual LAMP assay targeting the Omp25 gene. Sensitivity of the standardized visual LAMP assay and TaqManA (R) real-time PCR assay was determined by serial dilution of positive Brucella melitensis DNA (10(2) to 10(-4) ng) obtained from standard culture. The TaqManA (R) probe real-time assay can detect as low as 100 fg of B. melitensis DNA, whereas culture from vaginal swab washings has a limit of detection (LOD) of only 1 cfu/ml. Similarly, the visual LAMP assay can detect as low as 10 fg of B. melitensis DNA as compared to an LOD of 30 cfu/ml from culture of vaginal swab washings. Both assays were compared with serological tests (serum tube agglutination test (STAT) and indirect enzyme-linked immunosorbent assay (iELISA)) for diagnostic sensitivity and specificity. Diagnostic sensitivities and specificities for TaqManA (R) real-time PCR vs. LAMP assays were 98 and 100% vs. 100 and 97.8%, respectively. Results of visual LAMP assay indicated that LAMP is a fast, specific, sensitive, inexpensive and suitable method for diagnosis of B. melitensis infection under field conditions. On the other hand, Omp31 TaqManA (R) probe real-time assay can be used in conjunction with the other field-based diagnostic tests due to its high specificity.