ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR SCREENING OF MILK SAMPLES FOR SALMONELLA-TYPHIMURIUM IN DAIRY HERDS

We investigated the ability of an antibody-specific, O antigen-based E LISA to document Salmonella typhimurium herd infections by screening o f milk samples. Three cattle populations, 20 herds with no history of salmonellosis, 8 herds with history of S typhimurium epsiodes within t he previous 7 months, and 220 herds of unknown disease status, were te sted. A herd was considered ELISA positive if at least 5% of the cows had OD values > 0.3. Among the 20 herds without history of salmonellos is, only 2 herds were ELISA positive, whereas all 8 herds with a known history of salmonellosis were ELISA positive (herd specificity, 0.9 a nd herd sensitivity, 1.0). A sig nificant correlation (P < 0.001) was found between the OD values of serum and milk samples from cows in the herds with a history of salmonellosis. It was concluded that ELISA te sting of individual milk sam ples can be used for surveillance of herd s for S typhimurium infections, but further modifications are needed t o test bulk tank milk samples.