Indirect ELISA for the detection of a specific antibody response againstMycoplasma gallisepticum

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Abstract
An indirect enzyme‐linked immunosorbent assay (ELISA) was developed for determining Mycoplasma gallisepticum antibodies in chicken sera. The M. gallisepticum antigen was detergent extracted and incorporated into ISCOMs. Sediment of broth medium treated with sarcosyl was used as control antigen. Sera were tested before and after absorption with broth medium components and ELJSA titres are expressed as optical density (OD) at 492 nm. Sera from experimentally or naturally infected chickens, those vaccinated with Salsbury Mg bacterin or both vaccinated and experimentally infected were compared with sera from M. gallisepticum free or SPF chickens. A high OD was observed when unabsorbed sera (even from SPF chickens) were tested with control antigen. The non‐specific binding of M. gallisepticum negative sera could be removed by absorbing the sera with broth media components before the ELISA was performed. In contrast, ELISA titres obtained with sera from M. gallisepticum positive birds did not decrease significantly after absorption, except in the vaccinated and experimentally infected group. When the OD obtained with control antigen was subtracted from that obtained with ISCOM antigen, the mean value for M. gallisepticum free chickens was 0.083. Higher values were obtained with absorbed sera from experimentally or naturally infected (0.248–0.526), vaccinated (0.506), or vaccinated and infected (0.276–0.930) birds. The use of the ISCOM antigen presentation system in the indirect ELISA, combined with absorption of sera with broth components was demonstrated to be a useful diagnostic assay for M. gallisepticum antibodies.