Identification of specific antigens of Pseudomonas pseudomallei and evaluation of their efficacies for diagnosis of melioidosis.

Current methods for the diagnosis of melioidosis are based on bacteriological culture. A number of serological tests currently available lack specificity and sensitivity. This is largely due to the use of crude antigens which results in a significant cross-reactivity with sera from individuals infected with other bacteria. In this study five different antigens were prepared and evaluated for their potential usefulness in diagnosis of melioidosis. These included a 19.5-kDa antigen which was previously shown to be specific by Western blotting (immunoblotting), a crude cell extract, a veronal extract, a 39.0-kDa antigen, and an immunoaffinity-purified antigen. All antigens were used for detecting antibody in sera from patients with septicemic melioidosis by indirect enzyme-linked immunosorbent assay. The results were compared with those obtained with sera from patients with other bacterial infections and normal sera from areas where the infection is and is not endemic. The 19.5-kDa antigen exhibited the most satisfactory results, with 92% sensitivity, 91% specificity, 81% positive predictive value, and 96% negative predictive value based on a background obtained with normal sera from the area where the infection is nonendemic. These values were 82% sensitivity, 96% specificity, 94% positive predictive value, and 87% negative predictive value based on results with normal sera from the area where the infection is endemic. Results from this study showed that the 19.5-kDa antigen was potentially useful in the diagnosis of melioidosis and deserves further investigation.