Adjuvant effect of Escherichia coli heat labile enterotoxin B subunit against internal egg contamination in domestic fowl immunised with a live Salmonella enterica serovar Enteritidis vaccine

This study evaluated the effect of Salmonella enterica serovar Enteritidis (SE) secreting Escherichia coli heat labile enterotoxin B subunit (LTB) protein as an adjuvant for a live SE vaccine (JOL919) against virulent SE challenge in hens. The eltB gene encoding LTB was inserted into the Asd+ β-lactamase signal plasmid pJHL65. This plasmid was transformed into ΔlonΔcpxRΔasd SE to generate the LTB strain JOL1228. One-hundred female domestic fowl were divided into five groups and hens in immunised groups were primed and subsequently boosted with either JOL919 or a JOL919–JOL1228 mixture. Humoral and cellular immune responses were significantly higher in the immunised groups than the control group. On challenge with virulent SE, egg protection was 89.3% in immunised hens in group B (primed and boosted twice with JOL919 only), 89.3% in group C (primed with JOL919–JOL1228 mixture and boosted twice with JOL919), 100% in group D (primed and first booster with JOL919–JOL1228 mixture, then subsequently boosted with JOL919), 90.5% in group E (primed and boosted twice with JOL919–JOL1228 mixture) and 60.7% in group A (control group of non-immunised hens inoculated with phosphate buffered saline). The challenge strain was detected significantly less in all organs examined from hens in group D than those of the control group. These results indicate that vaccination with JOL1228, especially when added to priming and first booster immunisations, may reduce egg contamination with SE.