Maternal immunity induced by inactivated S. Typhimurium vaccine is less protective to S. Derby challenge than to S. Typhimurium challenge in suckling piglets

Salmonella enterica serovar Typhimurium and Salmonella enterica serovar Derby are the most common serovars of Salmonella enterica ssp. enterica found in pigs in Europe. We previously observed that suckling piglets of sows vaccinated with an S. Typhimurium-based inactivated vaccine are protected against homologous strain challenge. To develop this vaccine for commercial use, potential crossprotectivity of this vaccine to challenge with S. Derby was tested. Two sows were vaccinated with an S. Typhimurium-based inactivated vaccine while two other sows remained serologically negative. Four-day-old suckling piglets from both groups were orally challenged with S. Derby or S. Typhimurium. Maternally-derived immunity against S. Typhimurium protected piglets against S. Typhimurium challenge, when a significant (P < 0.05) decrease in S. Typhimurium count was found in ileocaecal and submandibular lymph node, tonsil, ileum and ileum content. On the other hand, after S. Derby challenge, significant (P < 0.05) decrease in S. Derby count was detected only in ileum content. Although both serovars belong to the same O:4 serogroup, other antigenic structures, for example the flagellin, are different. In a subsequent in-vitro experiment, we found that serum from vaccinated sows inhibited the motility of S. Typhimurium but not the motility of S. Derby. Our results indicate that protectivity of S. Typhimurium vaccine against S. Derby infection is limited.