Vaccination and early protection against non-host-specific Salmonella serotypes in poultry: exploitation of innate immunity and microbial activity

Abstract

A recent European Union Directive required member states to put monitoring and control programmes in place, of which vaccination is a central component. Live Salmonella vaccines generally confer better protection than killed vaccines, because the former stimulate both cell-mediated and humoral immunity. Administering Salmonella bacteria orally to newly hatched chickens results in extensive gut colonization and a strong adaptive immune stimulus but broiler chickens are immunologically immature. However, colonization exerts a variety of rapid (within 24 h) protective effects. These include specific colonization-inhibition (competitive exclusion) in which the protective bacteria exert a profound resistance to establishment and colonization by other related bacteria. This is thought to be primarily a metabolic attribute of the vaccinating bacteria but may also involve competition for attachment sites. The presence of large numbers of bacteria originating from a live Salmonella vaccine in the intestine can also induce infiltration of polymorphonuclear cells into the intestinal wall, which confers resistance to invasion and systemic spread by virulent Salmonella strains. This opens new perspectives for vaccine usage in broilers, layers and breeding poultry but also in other animals which show increased susceptibility to infection because of their young age or for other reasons, such as oral chemoprophylaxis or chemotherapy, where the lack of established normal gut flora is an issue. We recommend that all live vaccines considered for oral administration should be tested for their ability to induce the two protective effects described above. Further developments in live Salmonella vaccines are, however, currently hindered by fears associated with the use and release of live vaccines which may be genetically modified.

A colonisation-inhibition culture consisting of Salmonella Enteritidis and Typhimurium ΔhilAssrAfliG strains protects against infection by strains of both serotypes in broilers

“…This high susceptibility has been associated with the absence of normal gut microbiota [3,4] and the immature immune system of young chickens [5][6][7]. As a consequence, classical vaccination is not an effective means to achieve protection against Salmonella infection during the first days of life [14]. Alternatively, the use of organic acids, essential oils, proand prebiotics as feed supplements can help to control Salmonella infections in broiler chickens, but the protective responses elicited by these compounds only start several days post-hatch [22][23][24].…”

“…Earlier research showed that the colonisation-inhibition effect is more pronounced between isogenic strains and that there is greater inhibition within a serovar than between serovars [14,16,27]. Consequently, it is likely that the Salmonella Typhimurium hilAssrAfliG strain is not able to inhibit strains belonging to other serovars than Typhimurium.…”

“…By administering a CI strain that colonises the gut rapidly and extensively, it is possible to increase resistance to Salmonella strains quickly after hatching [12]. This concept has been recognised for a long time, and a great deal of effort has been put in developing strains that are appropriate for use as CI strains [13,14]. Earlier research demonstrated that deletion of the hilA, ssrA and fliG genes in a Salmonella Enteritidis strain resulted in a CI strain that was safe and effective in protecting broilers against challenge with a Salmonella Enteritidis wild-type strain [15].…”

Scientific Opinion on the public health risks of table eggs due to deterioration and development of pathogens

“…Clearance of primary S. Enteritidis and S. Typhimurium infection is dependent on age of the chicken and host genetics (Beal and Smith, 2007). Cell-mediated immunity plays a more important role than the humoral response in protection and against Salmonella infection (Van Immerseel et al, 2005). Wigley et al (2005) have demonstrated that at the onset of laying both the T-cell response to Salmonella and non-specific responses to mitogenic stimulation fall sharply in both infected and noninfected birds.…”

The contribution of genes required for anaerobic respiration to the virulence of Salmonella enterica serovar Gallinarum for chickens

“…Mutants were constructed in an identical way to the proton translocating-deficient mutants described previously (46). In brief, four primers were designed for each gene to be mutated such that two fragments close to the 5' and 3' ends ( Transductants were plated on LB agar containing spectinomycin or kanamycin and after incubation at 37C/24h…”