Development and evaluation of combined PCRs for detecting Salmonella in swine lymph nodes

Salmonellosis is one of the major zoonoses worldwide extended, frequently transmitted by subclinically infected pigs. Thus, EU health authorities have initiated salmonellosis control programs including prevalence studies in pigs by microbiological culture of lymph nodes (LN) following the ISO 6579 method. This method has some disadvantages that recommend the development of new diagnostic tools. The aim of this study was to develop and evaluate the usefulness of new PCRs for detecting Salmonella in LN pig samples, by amplifying 2 chromosomal (A and B) and 2 plasmidic (C and D) genes highly conserved in Salmonella. These PCRs were evaluated (i) in lab conditions; (ii) against 38 contaminants; (iii) against 132 Salmonella strains of 37 serotypes; and (iv) with 320 swine LN samples. Results shown that: (i) the four PCRs were specific for Salmonella; (ii) PCR-A and PCR-B had more sensitivity than PCR-C and PCR-D, unrelated to the serotype; (iii) PCR-A showed 94.4% SeR vs. the ISO method, while it was below 63.6% for the other genes; and (iv) best results of SeR was obtained by considering the 4 PCRs jointly, allowing to detect Salmonella in 26 ISO- samples, 17 (65.4%) of which resulted positive after a second culture. In conclusion, the combined PCRs showed higher diagnostic sensitivity, indicating its usefulness as a complementary or alternative method to the ISO