INDIRECT ELISA FOR THE DETECTION OF A SPECIFIC ANTIBODY-RESPONSE AGAINST MYCOPLASMA-GALLISEPTICUM

An indirect enzyme-linked immunosorbent assay (ELISA) was developed fo r determining Mycoplasma gallisepticum antibodies in chicken sera. The M. gallisepticum antigen was detergent extracted and incorporated int o ISCOMs. Sediment of broth medium treated with sarcosyl was used as c ontrol antigen. Sera were tested before and after absorption with brot h medium components and ELISA titres are expressed as optical density (OD) at 492 nm. Sera from experimentally or naturally infected chicken s, those vaccinated with Salsbury Mg bacterin or both vaccinated and e xperimentally infected were compared with sera from M. gallisepticum f ree 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 absorbi ng the sera with broth media components before the ELISA was performed . In contrast, ELISA titres obtained with sera from M. gallisepticum p ositive birds did not decrease significantly after absorption, except in the vaccinated and experimentally infected group. When the OD obtai ned 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 an d infected (0.276-0.930) birds. The use of the ISCOM antigen presentat ion system in the indirect ELISA, combined with absorption of sera wit h broth components was demonstrated to be a useful diagnostic assay fo r M. gallisepticum antibodies.