Cross-protection conferred by a live-attenuated Salmonella Enteritidis vaccine against Salmonella Heidelberg and Salmonella Infantis challenge

Salmonella infections cause enteric diseases in humans and animals, and poultry production is commonly associated with contamination by this foodborne pathogen. S. Enteritidis (SE) and S. Typhimurium (ST), as well as other serotypes such as S. Heidelberg (SH) and S. Infantis (SI), are highly prevalent.

This study evaluated the protection conferred by a live SE vaccine (auxotrophic for the amino acids adenine and histidine) in laying hens exposed to field strains of SH or SI. One-day-old pullets were randomly divided into vaccinated and unvaccinated groups. Birds in the vaccinated group (n=50) were immunized with Cevac® Salmovac on days 1, 6, and 13 via the oral route, while birds in the unvaccinated group (n=50) did not receive the vaccine.

At week 16, birds from each group were divided into two subgroups and challenged with an infectious dose of SH (10⁸ CFU/bird) or SI (10⁹ CFU/bird). At 3, 5, 10, and 14 days post-challenge (dpc), pathogen shedding was determined using individual cloacal swabs; the samples were enriched in tetrathionate broth, and the strain was then detected on XLD agar plates. In addition, at 5 and 14 dpd, five birds from each group were culled, and a Salmonella count was performed on the cecal contents.

SH excretion was significantly reduced in birds from the vaccinated group at 3 (p = 0.0001) and 5 (p < 0.0001) dpd compared with unvaccinated birds. The SH strain could not be detected in the ceca of the vaccinated birds analyzed on both sampling days. In contrast, SH was recovered from all unvaccinated birds sampled at 5 dpd and from 2/5 of the birds at 14 dpd.

A similar significant reduction in excretion was observed in vaccinated birds exposed to SI. SI excretion was significantly reduced in birds from the vaccinated group at 3 (p=0.0031), 5 (p=0.0001), and 10 (p=0.0079) dpd. SI could not be detected in vaccinated birds, but was recovered from 4 out of 5 unvaccinated birds sampled at 5 dpd and from 1 out of 5 birds at 14 dpd.

These results demonstrate that Cevac® Salmovac was able to significantly reduce the replication of the SH and SI challenge strains in vaccinated birds.