Salmonella Dublin is a common cause of calf illness, with high morbidity and mortality rates in affected animals, and is endemic in many regions of the U.S. and Canadian dairy industries.1–3 A 2016 report4 from the U.S. National Veterinary Services Laboratory found that S. Dublin was the most isolated Salmonella serotype obtained from ill cattle in the U.S. This serotype is also considered to be host adapted in bovine. Therefore, carrier animals that appear normal can be intermittent shedders and a source for maintaining the infection within a herd.3

Finding mechanisms to protect naïve animals from clinical disease caused by S. Dublin can reduce losses of animals and improve animal welfare in dairy herds. This includes maximizing transfer of passive immunity, maintaining high standards of hygiene, removing calves from the maternity environment as quickly as possible to reduce exposure of S. Dublin bacteria shed by carrier dams, and effective vaccination of dams and calves early in life.3

Traditional killed vaccines have failed to stimulate effective cell-mediated immune responses,9–11 so alternative vaccine technologies are needed. A possible strategy to induce effective immunity against S. Dublin is to target its iron-acquisition system. Iron is an essential nutrient of all gram-negative bacteria. In low-iron environments, such as in mammalian tissues, Salmonella manufacture and excrete low molecular weight proteins with a high affinity for iron called siderophores. Siderophores bind iron forming siderophore-iron complexes.

Siderophore receptor proteins (SRP®) are receptors located in the outer membrane of Salmonella bacteria and are responsible for transporting siderophore-iron complexes into the bacterial cell for use. Vaccines that utilize SRP® from S. Dublin should restrict the transportation of iron into the bacterium, thereby starving it of this required nutrient, resulting in cell death. Siderophore receptor proteins are highly conserved among gram-negative bacteria and are nearly identical within a genus, making them novel vaccine targets.