Comparison of egg yolk and serum for the detection of Mycoplasma gallisepticum and M. synoviae antibodies by enzyme-linked immunosorbent assay.

Egg yolk was evaluated in the enzyme-linked immunosorbent assay (ELISA) as an alternative source of antibodies for detection of Mycoplasma gallisepticum (MG) and M. synoviae (MS) infections in chickens. There was no statistically significant difference (P greater than 0.05) between the ELISA geometric mean titers (GMTs) of saline-diluted egg yolk and chloroform-extracted egg yolk, and both preparations had a high correlation coefficient (0.87 for MG; 0.97 for MS). The saline-diluted and chloroform-extracted yolk had a relative sensitivity of 90% and specificity of 98% in the MG ELISA; in MS ELISA they were 100% and 96%, respectively. Hemagglutination-inhibition (HI) results with chloroform-extracted samples were satisfactory, but those with saline-diluted samples were not. Neither preparation was satisfactory for use in the rapid plate agglutination (RPA) test. A 1-ml sample of yolk was compared with the whole-yolk method. The chloroform-extracted whole yolk yielded a significantly higher (P less than 0.05) GMT in the MG ELISA; however, there was no statistically significant difference (P greater than 0.05) between GMTs yielded by the two procedures in the MS ELISA. The correlation coefficients for the two sampling methods were 0.73 for MG ELISA and 0.63 for MS ELISA. ELISA detected no statistically significant difference (P greater than 0.05) between GMTs of serum and chloroform-extracted yolk from individual birds. Results with the HI test were comparable to those with ELISA on the same samples. The RPA test yielded comparable results on the serum samples. No statistically significant differences (P greater than 0.05) were observed in HI or ELISA antibody levels between egg-yolk samples and sera on random samples collected from nine flocks that were MG- and MS-free or were infected with MG, MS, or both; however, egg-yolk samples tended to have slightly higher titers than sera in both tests. The optimum screening dilution of chloroform-extracted yolk for detecting MG and MS antibodies by ELISA was 1:800.