Evaluation of Sonicated and Heat Extracted Lipopolysaccharide Brucella Abortus Antigens by an In House Enzyme Linked Immunosorbant Assay 801-804
Dr. Supriya Christopher
Department of Microbiology,
Kempegowda Institute of Medical Sciences,
Bangalore, India - 560070.
Aim: Brucellae are small gram negative coccobacilli that are known to cause brucellosis, the most common zoonotic disease world wide. The multisystem involvement and the protean and the unusual clinical presentation of the disease pose significant diagnostic challenges. Although the isolation of the causative organism is the definitive proof of the disease aetiology, practical difficulties are encountered. Hence, serological tests remain the most commonly used methods for its laboratory diagnosis. The standard tube agglutination test (STT) is the conventional serological test which is used.
Method: The present study was carried out to evaluate the two different antigenic preparations from the smooth stains of B. abortus S99 for standardizing the enzyme linked immunosorbant assay (ELISA) as an alternative for STT. The standard tube agglutination test antigen and the standard antibrucella serum which were obtained from IVRI, Izathnagar, were used as the controls for the standardization of the ELISA.
A sonicated lipopolysaccharide antigen (LPS-SE) and a heat extracted lipopolysaccharide antigen (LPS-HE) were evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and they were used to coat the micro titre plates for the enzyme linked immunosorbant assay. 81 human sera from people who were working in organized farms (cases), hundred human sera from apparently healthy persons (controls) and 100 Widal positive samples were selected to check for the crossreactivity for this study. All the serum samples (the cases , controls and the WIDAL positive samples ) were tested by the standard tube agglutination test (STT).This study was conducted over a period of four years at a tertiary care hospital in India.
Results: Among the 81 cases, eight (9.87%) sera gave a titre of ≥ 1:80 by STT, whereas by ELISA, 10(12.34%) and 9 (11.11%) cases showed significant titres on the LPS-SE and the LPS-HE coated plates respectively. The accuracy of the ELISA by using both LPS-SE and LPS â€“HE was 93.83% and 95.86%, with a p value of > 0.001, as compared to STT.
Conclusion: The overall seroprevalence with ELISA was 12.34% and 11.11% with the LPS-SE and the LPS-HE antigens, whereas it was 9.87% with STT. Hence, ELISA can be considered as a better diagnostic serological test for the diagnosis of brucellosis. It is cheap and reproducible and the antigen coated plates can be stored for longer periods.