Campylobacter is one of the most common bacterial pathogens of food safety concern. Campylobacter jejuni infects chickens by 2–3 weeks of age and colonized chickens carry a high C. jejuni load in their gut without developing clinical disease. Contamination of meat products by gut contents is difficult to prevent because of the high numbers of C. jejuni in the gut, and the large percentage of birds infected. Therefore, effective intervention strategies to limit human infections of C. jejuni should prioritize the control of pathogen transmission along the food supply chain. To this end, there have been ongoing efforts to develop innovative ways to control foodborne pathogens in poultry to meet the growing customers’ demand for poultry meat that is free of foodborne pathogens. In this review, we discuss various approaches that are being undertaken to reduce Campylobacter load in live chickens (pre-harvest) and in carcasses (post-harvest). We also provide some insights into optimization of these approaches, which could potentially help improve the pre- and post-harvest practices for better control of Campylobacter.

Necrotic enteritis (NE), caused by Clostridium perfringens (CP), is one of the most common of poultry diseases, causing huge economic losses to the poultry industry. This review provides an overview of the pathogenesis of NE in chickens and of the interaction of CP with the host immune system. The roles of management, nutrition, probiotics, and vaccination in reducing the incidence and severity of NE in poultry flocks are also discussed.

There is evidence that probiotic lactobacilli, in addition to essential vitamins, such as vitamin A and D, have immunomodulatory properties that enhance immune response of neonatal chickens against infections. The present study evaluated the effects of in ovo administration of retinoic acid (RA), 25-Hydroxyvitamin D₃ (VitD), and a lactobacilli cocktail on cytokine gene expression, antibody responses and spleen cell subsets in chickens. RA (90 µmol/egg) and VitD (0.6 μg/egg) were administered in ovo, either alone or in combination with lactobacilli (10⁷ CFU/egg), at embryonic d 18. On d 5 and 10 posthatch, gene expression and cellular composition were analyzed in the bursa of Fabricius and spleen. Birds were immunized on d 14 and 21 posthatch with 2 T-dependent antigens, sheep red blood cells (SRBC) and keyhole limpet hemocyanin (KLH), to assess their antibody responses. Sera were collected from the immunized chickens on d 14, 21, 28, and 35 posthatch. The results demonstrated that lactobacilli treatment increased the number of monocyte/macrophages (KUL01⁺) and CD3⁺CD4⁺ T cells in the spleen, and enhanced serum anti-KLH IgM and IgY on d 14 postprimary immunization (P < 0.05). RA significantly increased serum IgY and IgM titers to KLH and enhanced the expression of interferon (IFN)-α, interleukin (IL)-1β, IL-6, IL-8, IL-12, IL-13, and transforming growth factor-β (TGF-β) in the bursa of Fabricius (P < 0.05). The percentage of CD3⁺CD8⁺ T cells, and monocyte/macrophages (KUL01⁺) was elevated in the spleen as well (P < 0.05). These findings reveal that prehatch administration of RA improves immunocompetency of neonatal chickens by increasing the production of cytokines that regulate innate immunity and through enhancing antibody-mediated response against T-dependent antigens.

Gamma delta (γδ) T cells play a significant role in the prevention of viral infection and tumor surveillance in mammals. Although the involvement of γδ T cells in Marek’s disease virus (MDV) infection has been suggested, their detailed contribution to immunity against MDV or the progression of Marek’s disease (MD) remains unknown. In the current study, T cell receptor (TCR)γδ-activated peripheral blood mononuclear cells (PBMCs) were infused into recipient chickens and their effects were examined in the context of tumor formation by MDV and immunity against MDV. We demonstrated that the adoptive transfer of TCRγδ-activated PBMCs reduced virus replication in the lungs and tumor incidence in MDV-challenged chickens. Infusion of TCRγδ-activated PBMCs induced IFN-γ-producing γδ T cells at 10 days post-infection (dpi), and degranulation activity in circulating γδ T cell and CD8α⁺ γδ T cells at 10 and 21 dpi in MDV-challenged chickens. Additionally, the upregulation of IFN-γ and granzyme A gene expression at 10 dpi was significant in the spleen of the TCRγδ-activated PBMCs-infused and MDV-challenged group compared to the control group. Taken together, our results revealed that TCRγδ stimulation promotes the effector function of chicken γδ T cells, and these effector γδ T cells may be involved in protection against MD.

Dietary antibiotics, including antibiotic growth promoters (AGPs), have been commonly used to improve health and growth of poultry. The present study investigated the effects of therapeutic doses of dietary antibiotics, including bacitracin methylene disalicylate (BMD), penicillin G potassium (PP) and an ionophore (salinomycin, SA), on the cecal microbiome of chickens. BMD and SA treatments were given as dietary supplements from d 1 to 35 of age. The SAPP (salinomycin+ penicillin G potassium) group was given SA as a dietary supplement from d 1 to 35 of age and PP was added to drinking water from d 19 to 24 of age to simulate common practices for control of necrotic enteritis in broilers. The cecal contents were collected from all treatment groups on d 10, 24, and 35 of age and DNA was extracted for metagenomic analysis of the cecal microbiome. The results revealed that dietary or water supplementation of therapeutic levels of antibiotics and ionophores to chickens significantly altered the cecal microbial homeostasis during different stages of the chicken life. The alpha diversity analysis showed that BMD, SA, and SAPP treatments decreased diversity and evenness of the cecal microbiome of treated chickens on d 10 of age. Species richness was also reduced on d 35 following treatment with BMD. Beta diversity analyses revealed that SAPP and BMD induced significant changes in the relative abundance of Gram-positive and -negative bacteria on d 10, while no significant differences were observed on d 24. On d 35, the non-treated control group had higher relative abundance of unclassified Gram-positive and -negative bacteria compared to SA, SAPP, and BMD treatment groups. Overall, despite their beneficial role in controlling necrotic enteritis outbreaks, the findings of this study highlight the potential negative effects of dietary supplementation of therapeutic levels of antibiotics on the gut microbiome and suggest that adjusting gut bacteria may be required to restore microbial richness and diversity of the gut microbiome following treatment with these antibiotics.

Salmonella is among the most important foodborne pathogens impacting public health and food safety. In humans, Salmonella infections are typically caused by the consumption of raw or undercooked poultry products. Therefore, controlling Salmonella at the poultry farm level is crucial. The main focus of this review article is recent advancements in vaccination strategies aimed at reducing Salmonella colonization in poultry. To provide essential context, it briefly outlines Salmonella transmission, pathogenesis, and host immune responses. The review explores the development and application of various vaccine types, including live-attenuated, killed, subunit, and ghost vaccines, and evaluates their immunological mechanisms, safety, and effectiveness. It also discusses limitations of current vaccines and the need for innovative approaches such as nanoparticle-based oral vaccines. Finally, the article offers recommendations for optimizing vaccination programs to protect both poultry health and food safety.