Use of muscle fluid as a source of antibodies for serologic detection of Salmonella infection in slaughter pig herds.

Fluid drained from a muscle tissue sample was used as an alternative to serum for the detection of specific anti-Salmonella antibodies in an indirect LPS enzyme-linked immunosorbent assay (ELISA). In the first study, serum and muscle fluid from 3 pigs experimentally infected with Salmonella typhimurium showed parallel dilution-response relationships when ELISA optical density (OD) values were plotted against sample dilution. ELISA results obtained with serum diluted 1:400 corresponded to those from muscle fluid diluted 1:30. In a second study, using the predetermined dilutions of individually paired serum and muscle fluid samples from 103 pigs, a high degree of concordance between the serum ELISA and the muscle fluid ELISA was observed. Limits of agreement between the 2 methods were calculated as -8.9 to 12.3 OD%, which was considered acceptable. The muscle fluid ELISA had specificities of 0.91-1.0 and sensitivities of 0.80-0.89 at various cutoff values as compared with the serum ELISA. Muscle fluid is a useful postmortem alternative to serum when used with an ELISA to detect anti-Salmonella antibodies.