Salmonella is a pathogenic bacterium isolated from pig intestines during the cholera epidemic of 1885 (Steele, 1963). Salmonella is a gram-negative bacterium that belongs to the family Enterobacteriaceae and is an acidophilic facultative anaerobic bacterium that can rely on systemic flagellar motility (GBD 2017 Non-Typhoidal Salmonella Invasive Disease Collaborators, 2019). Infection with Salmonella typically presents with nonspecific clinical symptoms (Popa and Papa, 2021). To date, more than 2,600 serotypes of Salmonella have been detected (Teklemariam et al., 2023). S. bongori was the first subspecies isolated, and S. Enteritidis and S. Typhimurium were the two most common serotypes, followed by S. Newport, S. Javiana, and S. Heidelberg (Dos Santos et al., 2019; Oh and Park, 2017). The global burden of invasive non-typhoidal Salmonella (iNTS) disease is considerable, contributing to significant morbidity and mortality, particularly among vulnerable populations. By contrast, non-typhoidal Salmonella (NTS) more commonly causes gastroenteritis. In the United States alone, Salmonella is estimated to cause about 1.35 million infections, 26,500 hospitalizations, and 420 deaths annually (Acevedo-Villanueva et al., 2021).

Different serotypes of Salmonella lead to differential clinical manifestations. S. Enteritidis infection typically causes diarrhea, abdominal pain, nausea, vomiting, and fever. S. Typhimurium causes mainly acute infectious diseases, such as gastroenteritis and septicaemia. The symptoms of the gastroenteritis type are similar to those of S. Enteritidis, and the septicemia type may cause symptoms of systemic infection (Ferrari et al., 2019). Salmonella is widely distributed in nature, spreads easily, has many types, and is difficult to eradicate (Thomas et al., 2013). This diversity implies that single, serotype-specific control measures may have limited overall impact, necessitating broader or combined therapeutic and preventive approaches. Its zoonotic characteristic, with transmission occurring between animals and humans, underscores the need for control efforts that span human, animal, and environmental domains, aligning with the one health concept.

Salmonellosis imposes a significant economic burden, with estimated annual costs in the United States rising from $1 billion in 1987 to approximately $3.3 billion in recent years, ranking it third among foodborne pathogens (Lobertti et al., 2024). These estimates likely underrepresent the true burden, as they often exclude intangible costs such as pain and suffering, lost leisure time and long-term health consequences. Additionally, losses in the agricultural sector due to reduced animal productivity, regulatory interventions and product recalls further underscore the need for cost-effective and sustainable control strategies. This significant economic toll highlights the urgent need for cost-effective and sustainable control measures. Biological therapies, if proven to be more effective or sustainable than current methods, particularly in the face of antimicrobial resistance, could offer substantial economic benefits by reducing healthcare expenditures and productivity losses, thereby justifying continued investment in their research and development.

Since their discovery in the twentieth century, antibiotics have been the mainstay of treatment for salmonellosis. For example, Conventional antibiotics including chloramphenicol (inhibiting peptide chain elongation to block protein synthesis) (Kunstadter et al., 1951); quinolone antibiotics (levofloxacin, ciprofloxacin) interfere with bacterial growth and reproduction by preventing DNA replication and RNA transcription (Macías-Farrera et al., 2018); third-generation cephalosporins inhibit cell wall synthesis and thus exert an inhibitory effect (Schmidt et al., 2022); and different antibiotics have shown good therapeutic effects on Salmonella (Braetz et al., 2022; Gebeyehu et al., 2022; Jacks et al., 1981). However, the widespread and often injudicious use of antibiotics in human and veterinary medicine has led to a dramatic increase in antimicrobial resistance (AMR) (Feye et al., 2016). Salmonella strains undergo genetic mutations, rendering them resistant to antibiotics to which they were previously susceptible, leading to bacterial populations with increased overall resistance (Mathew et al., 2009). Aslam et al. reported a high prevalence of antimicrobial resistance among Salmonella isolates recovered from retail meats, with multidrug resistance being frequently observed. Resistance was particularly common to several clinically and veterinary important antimicrobials, and distinct resistance gene profiles were associated with specific Salmonella lineages, indicating that foodborne Salmonella constitutes a significant reservoir of antimicrobial resistance (Aslam et al., 2012).

Beyond antimicrobial resistance, antibiotic tolerance has increasingly been recognized as a distinct and clinically relevant contributor to treatment failure in Salmonella infections (Fanous et al., 2025). Tolerance is mainly manifested as the prolonged survival time of bacteria under antibiotic exposure (Pontes and Groisman, 2019). This physiological state markedly diminishes the efficacy of many conventional antibiotics whose bactericidal activity depends on active cellular processes, including cell wall synthesis, DNA replication, and protein translation. As a consequence, intracellular Salmonella can survive prolonged antibiotic treatment, contributing to delayed clearance, relapse, and chronic infection. Recent studies have highlighted antibiotic tolerance as a major physiological consequence of Salmonella’s adaptation to the intracellular niche and a key determinant of treatment failure despite apparent in vitro susceptibility (Wijburg et al., 2000; Fields et al., 1986). This phenomenon poses a serious threat to global public health and could cause approximately 10 million deaths annually by 2050 if it is not effectively controlled (Munshi et al., 2025; Lamichhane et al., 2024).

In response to the AMR crisis, biological therapies, including bacteriophages (phages) (Kortright et al., 2019), probiotics (Aghamohammad and Rohani, 2023), and vaccines (Frost et al., 2023), have emerged as promising alternatives for the treatment and control of salmonellosis. These approaches offer the potential for high efficacy with minimal side effects compared to conventional antibiotics. Generally, phages function by directly destroying the bacterial cell structure; probiotics modulate the intestinal environment, compete with pathogens, and stimulate host immunity; and vaccines induce specific, long-lasting immune protection. The “promise” of these biotherapies extends beyond their direct antimicrobial effects. Their potential for more targeted action. This review aims to compile the most up-to-date information on these biotherapeutic modalities for zoonotic salmonellosis, encompassing their methods of application, underlying mechanisms of action, functional benefits, and progress in clinical research. Furthermore, it seeks to provide a theoretical foundation for future research directions and facilitate the establishment of safer, more effective Salmonella control systems.

Bacteriophages are the most ubiquitous biological organisms in nature. They are viruses that can infect bacteria (Dion et al., 2020). Compared with broad-spectrum antibiotics, phages have high specificity and do not damage coexisting bacterial flora; they have the advantages of wide distribution, simple isolation, a short development cycle, low cost, relatively strong environmental stability under specific conditions, and low toxicity and side effects (Doss et al., 2017; Strathdee et al., 2023). Bacteriophages are divided into lytic phages (which attach to host cells and replicate by releasing new phages) and temperate phages (which integrate their genome into the host cell and replicate) (Hobbs and Abedon, 2016) (Figure 1).

For therapeutic applications, strictly lytic phages are overwhelmingly preferred due to significant safety concerns associated with temperate phages. Temperate phages carry the inherent risk of horizontal gene transfer, potentially transferring virulence factors or antibiotic resistance genes from the phage genome or the host bacterium to other bacteria (Monteiro et al., 2019). Furthermore, their lytic conversion is unpredictable and dependent on environmental cues, which compromises treatment reliability. Consequently, lytic phages, which offer immediate and controlled bactericidal effects without the risk of genetic transfer, are the exclusive choice for current clinical applications, unless lysogenic variants are genetically modified to irreversibly disable their integration capabilities. This fundamental safety consideration dictates phage selection criteria and informs strategies for phage engineering (Dion et al., 2020).

Phages also address another critical challenge in Salmonella infections - the formation of recalcitrant biofilms. Biofilms are complex, sessile microbial communities living on surfaces and interfaces where organisms produce a matrix of extracellular polymeric substances (EPS) (Flemming et al., 2023). This mode of growth provides bacteria, including Salmonella, with a protected microenvironment, significantly increasing their resistance to antibiotics and host immune defenses. The ability of phages to disrupt biofilms represents a critical advantage, extending their utility beyond acute planktonic infections to persistent, hard-to-treat biofilm-associated conditions (Yin et al., 2019; Roy et al., 2018). Rashad et al. demonstrated that in vitro applications of phage LPSent1 inhibited free planktonic cells and biofilms of S. Enteritidis EG. SmE1. Furthermore, this inhibition was associated with a reduced emergence of phage-resistant bacterial mutants (Al-Hindi et al., 2023; Geredew Kifelew et al., 2019). Consistent with this work, Yifeng et al. reported that treatment with phage T102 markedly inhibited biofilm formation and reduced the population of S. Typhimurium ATCC14028 (Ding et al., 2023). Additionally, Kwon et al. (2021) reported that the biomass decreased steeply within 6 h after Salmonella was treated with the high or low concentration phage pSal-SNUABM-02, demonstrating the antibacterial effects of the phage against Salmonella. At the same time, phages combined with antibiotics and phage cocktails have also been shown to be effective. As phages can disrupt biofilm structure, antibiotics more easily penetrate and reach bacteria. Min lu et al. reported that the combination of phage ST-3 with levofloxacin hydrochloride caused a significant decrease in biofilm biomass, which in turn contributed to a higher clearance rate of S. Typhimurium CGMCC 1.1174 than monotherapy. Katarzyna et al. reported that mixing phage cocktails vB-Sen-TO17 and vB-SenM-2 with 12.5 μg/mL tetracycline, 50 μg/mL colistin and enrofloxacin, respectively, enhanced the therapeutic efficacy of antibiotics on Salmonella and delayed the development of Salmonella resistance to antibiotics (Kosznik-Kwaśnicka et al., 2022). These findings underscore the potential of integrated phage-antibiotic therapies to enhance treatment efficacy, overcome resistance limitations, and optimize pathogen control strategies. Future research should explore mechanistic interactions and clinical scalability of such combinatorial approaches.

With a growing body of research validating its efficacy, phage therapy is becoming a promising alternative for salmonellosis treatment, as evidenced by increasing clinical trials demonstrating its translational potential. Despite the advantages of phage therapy, several limitations and challenges remain. First, many natural phages have a narrow host range, meaning a specific phage may only be effective against a limited number of bacterial strains or serovars, necessitating careful matching or the use of phage cocktails to broaden coverage. Second, bacteria can develop resistance to phages, although this can sometimes be mitigated by using cocktails or isolating/engineering new phages. Third, there is a lack of large-scale, rigorously controlled clinical trials that meet stringent medical and regulatory standards, which are essential for confirming safety and efficacy. Fourth, large-scale phage production poses challenges in ensuring purity, stability, cost-effectiveness, and consistency-particularly for cocktails. Additionally, regulatory pathways for phage therapy are still evolving in many regions, creating uncertainty for developers.

Future directions focus on overcoming these barriers. There is an urgent need for robust pharmacokinetic and pharmacodynamic (PK/PD) studies to determine optimal dosing and administration routes and to better understand phage behavior in vivo. Engineering phages with broader host ranges, stronger lytic activity, and resistance to bacterial defense mechanisms is a key research priority. Standardizing phage cocktail formulations and improving delivery systems (e.g., microencapsulation) to protect phages and enhance targeted delivery are also critical. Beyond these technical and regulatory hurdles, the development of engineered phages introduces additional biosafety and ecological considerations. Engineering phages with broader host ranges or enhanced lytic activity may pose risks to beneficial commensal microbiota in the animal gut, and raises concerns regarding unintended environmental dissemination following release from treated hosts. To mitigate these risks, proposed strategies include the use of strictly lytic phages, genetic safeguards to limit phage persistence or horizontal gene transfer, controlled dosing and administration routes, and post-treatment environmental monitoring under robust regulatory oversight (Liu et al., 2022).

Probiotics are live microorganisms that, when ingested in adequate amounts, can enhance the intestinal flora by modulating immune responses, activating immune regulatory functions, and inhibiting the growth of pathogens (Kim et al., 2019), which are used to improve the health of the host and provide health benefits to the host. Probiotic microorganisms are widely found in water, soil, plants, and animal foods (Suez et al., 2019). Probiotics employ a multifaceted arsenal of mechanisms to combat Salmonella infection, often acting simultaneously through direct antagonism and indirect host-mediated effects. This multi-pronged approach may offer more robust and resilient protection compared to therapies with a single mode of action.

Chen Pei et al. stimulated mouse monocyte macrophages with Lactobacillus plantarum RS-9. Lactobacillus plantarum RS-09 can reduce splenomegaly caused by S. Typhimurium, and Lactobacillus plantarum can interact with macrophages to prevent bacterial enteropathy because of its ability to modulate macrophage polarization, upregulate the generation of M1 macrophages and induce TLR2-associated NF-κB signaling activity against S. Typhimurium (Zhao et al., 2022). In 2023, Aixin et al. studied Lactobacillus plantarum postbiotics. Turbidimetry and agar diffusion experiments revealed that Lactiplantibacillus plantarum-derived postbiotics (LPC) directly reduced Salmonella growth. Real-time PCR and biofilm inhibition assays revealed that LPC strongly suppressed Salmonella pathogenicity by reducing the expression of virulence genes (SopE, SopB, InvA, InvF, SipB, HilA, SipA and SopD2), pili genes (FilF, SefA, LpfA, FimF), flagellum genes (FlhD, FliC, FliD) and biofilm formation genes. LP probiotics were more effective than LPs in attenuating ST-induced intestinal damage in mice, as indicated by increased villus/crypt ratios and increased expression levels of tight junction proteins (Occludin and Claudin-1).

The concept of using multistrain probiotic formulations is based on the rationale that a combination of different probiotic strains, potentially with complementary mechanisms of action, may offer enhanced protective effects compared to single-strain probiotics. This approach mirrors the strategy behind phage cocktails, aiming for broader efficacy and resilience. Chihua et al. demonstrated that multistrain probiotics have a better protective effect against Salmonella infection and concluded that compound probiotics are better than single-strain probiotics (Chang et al., 2020). Probiotics and medicines can also be used together to lower S. Typhimurium expression. Zul’s use of the combination of probiotics and Ajwain extract (which has the effects of clearing bacterial infections, improving oxidation, and inhibiting inflammation) proves this point of view (Haq et al., 2022). Huixianwu et al. further completed a simulation experiment involving the combination of probiotics on the basis of the finding that three probiotics can attenuate Salmonella. Microencapsulation technology is used to increase the stability and survival rate of probiotics. These findings indicate that microencapsulated probiotics are superior to free probiotics (Upadhaya et al., 2016).

The term “synbiotics” refers to combinations of probiotics and prebiotics (non-digestible food ingredients that selectively stimulate the growth and/or activity of beneficial bacteria in the colon). While the original manuscript mentions synbiotics in the context of protecting the intestinal barrier against S. Typhimurium infection, detailed exploration of synbiotic formulations specifically for Salmonella control is an area for further research. The exploration of multistrain probiotics and their combination with other beneficial agents reflects a broader principle in biotherapeutics: combining agents with diverse yet complementary mechanisms can lead to enhanced overall efficacy and a more robust therapeutic outcome.

Postbiotics are emerging as a significant evolution in the field of microbe-based therapies (Żółkiewicz et al., 2020). Defined as a “preparation of inanimate microorganisms and/or their components that confers a health benefit on the host”postbiotics include non-viable bacterial cells, cell fractions (like cell wall components, teichoic acids), and metabolites secreted by live bacteria (such as short-chain fatty acids (SCFAs), enzymes, peptides, and organic acids) (Cortés-Martín et al., 2020). The mechanisms of action of postbiotics are diverse and overlap with those of live probiotics. They can modulate the gut environment by reducing intestinal pH, enhance epithelial barrier functions, regulate local and systemic immune responses (often by upregulating anti-inflammatory cytokines and downregulating pro-inflammatory signals), and exert direct antimicrobial activity (Wuethrich et al., 2021). For instance, SCFAs, key postbiotic metabolites, serve as energy for colonocytes and can inhibit pathogen growth (Nataraj et al., 2020).

A compelling example is the use of LPC. LP postbiotics significantly reduced ST-induced inflammation by regulating the levels of inflammatory cytokines (increased IL-4 and IL-10 and decreased TNF-α) (Hu et al., 2023). Furthermore, LP postbiotics inhibited the activation of the NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome by decreasing the protein expression of NLRP3 and Caspase-1 and the gene expression of Caspase-1, IL-1β, and IL-18. Moreover, both LPC and LPB noticeably activated autophagy during ST infection, as indicated by the upregulated expression of LC3 and Beclin1 and the downregulated p62 level (p < 0.05). Finally, we found that LP postbiotics could trigger the AMP-activated protein kinase (AMPK) signaling pathway to induce autophagy.

Postbiotics offer several distinct advantages over live probiotics, directly addressing many of their practical limitations. These include enhanced stability (less sensitive to heat, oxygen, humidity, and gastric acidity), a superior safety profile (no risk of administering live microbes, especially crucial for immunocompromised individuals, children, or premature neonates), longer shelf-life, and potentially easier standardization, storage, and transport. These characteristics make postbiotics highly attractive for broader clinical and commercial development. Furthermore, research into postbiotics helps to deconstruct the beneficial effects of live probiotics by identifying the specific bioactive molecules responsible. This allows for a more precise, mechanism-based therapeutic development, moving from using the “whole organism” to utilizing its defined “active ingredients,” which aligns more closely with traditional pharmacological approaches.

The field of probiotic research is evolving beyond traditional strains, with increasing interest in “Next-Generation Probiotics” (NGPs). NGPs are novel microbial strains, often commensals isolated from the human gut, that exhibit specific health benefits and are typically developed with a pharmaceutical application in mind, sometimes referred to as Live Biotherapeutic Products (LBPs) (Li et al., 2024). These represent a shift toward more targeted and potentially more potent interventions. An example of an NGP with potential relevance is Akkermansia muciniphila. This Gram-negative bacterium colonizes the mucus layer of the human gut and is considered a promising NGP due to its various beneficial effects, including enhancing intestinal barrier integrity and modulating host immune responses, which could indirectly help protect against pathogens like Salmonella (Li et al., 2024; Ma et al., 2022). Furthermore, Micromycin produced by Sassone-Corsi’s E. coli Nissle 1917 strain (EcN) can displace pathogenic Enterobacteriaceae species under specific environmental conditions, demonstrating that MccH47 can inhibit the growth of Salmonella in vitro (Sassone-Corsi et al., 2016). Therefore, Jacob developed the probiotic MccH47 with an induction system (an ECN-engineered strain containing a plasmid system of mchAXIBCDEF and ttrRSBCA). The EcN-engineered strain carries a plasmid system that inhibits the ability of Salmonella to grow when exposed to tetrasulfate, a molecule produced in the inflamed gut during Salmonella infection. MccH47 is created under the action of tetra sulfate, verifying the suppression and competition of Salmonella in in vitro tests (Palmer et al., 2018). In the future, in vivo simulation experiments will be used to achieve stable chromosomal integration, and the results will be subsequently applied to the clinical trial stage. In the near future, this genetically designed probiotic medicine will play an important role in clinical practice.

While probiotics show promise in combating Salmonella infections, their clinical application faces several challenges:1. Stability and Storage Constraints. Many probiotic strains are sensitive to heat, oxygen, and humidity. Exposure to temperatures above 25 °C during storage or transport can significantly reduce viability, compromising therapeutic efficacy. 2. Variable Therapeutic Outcomes. The gut microbiota composition, immune status, age, and genetic background of the host influence probiotic colonization and efficacy. In addition, the inherent stability and colonization resistance of the resident gut microbiota often limit the persistence and functional impact of administered probiotics, contributing to substantial inter-individual variability in therapeutic outcomes. 3. Salmonella-induced gut inflammation may alter the mucosal environment, hindering probiotic adhesion and persistence. 4. Chronic probiotic use might disrupt indigenous flora balance or delay post-infection microbiome recovery. 5. Lack of Clinical Protocols: Limited large-scale human trials hinder consensus on treatment duration, strain combinations, or adjuvant therapies. 6. High-quality control requirements and cold-chain logistics increase costs, limiting accessibility in resource-limited regions.

Future research in probiotic therapy should focus on overcoming these limitations. Key priorities include the development of engineered probiotics with enhanced characteristics, such as improved acid and bile resistance for better survival in the gastrointestinal tract, and targeted antimicrobial properties for greater efficacy against specific pathogens like Salmonella. As discussed previously, exploring postbiotic alternatives, such as heat-killed probiotics (paraprobiotics) and specific metabolite-based therapies (e.g., LP postbiotics), represents a highly promising avenue. These non-viable preparations could circumvent the challenges associated with the stability and viability of live probiotic formulations, offering more reliable and potentially safer strategies for combating Salmonella infections. Similar to phage therapy, a key overarching challenge for probiotics is to ensure consistent efficacy and overcome practical issues of viability and delivery to translate their in vitro and preclinical promise into reliable clinical outcomes and widely available commercial products. The increasing focus on postbiotics is a direct response to these viability-related challenges.

As a cornerstone of One Health approaches, vaccination represents the most sustainable intervention for controlling Salmonella transmission across human-animal-environment interfaces (Adams et al., 2011). Three principal vaccine platforms have been developed against Salmonella: inactivated (killed) vaccines, attenuated vaccines, and subunit vaccines. While inactivated vaccines reliably induce humoral immunity through antibody production, their inability to stimulate robust cellular immune responses limits long-term protection. In contrast, attenuated vaccines-developed through precise genetic modifications to reduce virulence while maintaining immunogenicity-offer distinct advantages:1. they mimic natural infection to elicit both mucosal IgA and systemic IgG responses, 2. they activate CD4 + and CD8 + T-cell immunity critical for intracellular pathogen clearance, and 3. they often require fewer doses due to their capacity for limited replication in host tissues (Chen et al., 2021). These superior immunogenic properties, combined with practical advantages in administration, have positioned attenuated vaccines as the preferred choice for both human and veterinary applications (Table 3).

The remarkable success of mRNA vaccine technology during the COVID-19 pandemic has spurred interest in its application to other infectious diseases, including bacterial infections like salmonellosis. mRNA vaccines work by delivering genetic instructions (in the form of mRNA encoding specific antigens) to host cells, which then produce the antigen, triggering an immune response. This platform offers potential for rapid development and adaptation, as antigen sequences can be quickly designed and synthesized. While research into mRNA vaccines for Salmonella is still in its early stages, it represents a promising new frontier (Ramachandran et al., 2022). The rapid technology transfer from virology to bacteriology highlights the adaptability of this platform. Viral vectors, where genes encoding Salmonella antigens are inserted into harmless viruses, are another strategy, although less prominently featured for Salmonella in recent snippets compared to mRNA or direct Salmonella-based vectors for multivalent vaccines.

Nanoparticle (NP)-based delivery systems are emerging as a powerful tool to enhance the efficacy of vaccines, particularly subunit and oral vaccines, against pathogens like Salmonella. NPs can protect vaccine antigens from degradation (e.g., in the harsh environment of the gastrointestinal tract for oral vaccines), improve their stability, facilitate controlled or sustained release (creating a “depot effect”), enhance antigen uptake and presentation by antigen-presenting cells (APCs), and act as adjuvants themselves to boost immunogenicity (Wang et al., 2023). Chitosan nanoparticles (CNPs) have been investigated for oral delivery of Salmonella antigens in broilers. Studies have shown that CNP-encapsulated Salmonella vaccines can reduce gut permeability changes induced by infection, decrease S. Enteritidis load in the ceca, spleen, and small intestine, and increase levels of antigen-specific IgY and IgA. The positive surface charge of chitosan NPs facilitates adherence to negatively charged mucosal surfaces, aiding antigen delivery to mucosal immune inductive sites. Polymeric nanoparticles, in general, can be tailored in size (typically 10–500 nm) to optimize uptake by APCs and can be designed for pH-responsive release of antigens (Acevedo-Villanueva et al., 2021). Nanoparticle delivery systems are particularly crucial for developing effective oral killed vaccines, as they address the major hurdle of antigen degradation in the GI tract, thereby enabling efficient mucosal immune stimulation (Wang et al., 2023; Wang et al., 2023).

While preclinical research on novel Salmonella vaccines is vibrant, the translation to human clinical trials, particularly for NTS, is an ongoing process. Existing clinical trial data, as summarized in Table 4, predominantly focuses on vaccines against typhoidal Salmonella strains, such as S. Typhi and S. Paratyphi. These trials have evaluated various candidates, including the Typhoid Vi polysaccharide vaccine, Vi-CRM197 conjugate vaccine, the live attenuated M01ZH09 (S. Typhi Ty2 ΔaroC ΔssaV), and the live oral attenuated CVD 1902 for S. Paratyphi A. These trials have assessed immunogenicity (e.g., antibody responses) and safety in diverse populations, including adults and children in various geographical regions.

As vaccine research advances, experts have learned that they can offset the weaknesses of vaccines when they are used in combination. Research has evaluated protein formulations as vaccine candidates, comparing their immune response, protection, and organ clearance. The results showed that the recombinant protein had good immunogenicity. These findings indicate that the protein preparation has a protective effect on Salmonella infection and that the combination of RBapB, Rompa, and ROmpC has a good protective effect and organ clearance effect on the challenge of virulent S. Typhimurium and S. Enteritidis.

To address the issue of drug resistance induced by antibiotics used during the early stages of salmonellosis treatment. Jiangang determined that the S. Enteritidis live vaccine (Sm24/Rif12/SSQ strain) can prevent S. Enteritidis infection and studied whether the use of antibiotics affects the colonization of the oral live vaccine. The ecological balance of intestinal microorganisms is disrupted by oral or intramuscular injection of antibiotics and then vaccination with Salmonella (Sm24/Rif12/SSQ strain). Live attenuated Salmonella vaccine strains were finally isolated (Huberman et al., 2019).

In addition, attenuated strains obtained through genetic engineering that are safe but still immunogenic can be further engineered by introducing additional coding; the resulting multivalent vaccine candidates should be able to challenge the vector vaccine itself as well as additional target pathogens with biologically relevant protective immune responses (Galen et al., 2021).

Vaccines offer numerous advantages, including the potential to confer long-term immunity, prevent primary infection, reduce pathogen shedding, and contribute to the development of herd immunity within a population. However, the development of Salmonella vaccines is not without limitations. As mentioned above, the serotype specificity of many traditional vaccines is a major obstacle for NTS. Safety concerns, as well as the costs of vaccine development, production, and deployment, can be substantial, particularly for novel vaccine platforms. Some vaccines may require multiple injections or booster doses to achieve and maintain protective immunity, and adverse reactions may occur.

Future directions in Salmonella vaccine research are aimed at overcoming these limitations. A primary goal is the development of broadly protective NTS vaccines, leveraging multivalent antigen strategies, reverse vaccinology to identify conserved epitopes, and novel platforms like bacterial ghosts. Advancing mRNA and nanoparticle-based delivery systems for Salmonella antigens holds promise for improved immunogenicity and potentially faster development timelines. The development of more effective and safer adjuvants, particularly for subunit and mucosal vaccines, is crucial. Oral vaccine formulations that can efficiently induce robust mucosal immunity are highly desirable for enteric pathogens. Additionally, the development of DIVA (Differentiating Infected from Vaccinated Animals) vaccines is important for disease surveillance and control programs in livestock. Ultimately, achieving a broadly protective, safe, and cost-effective NTS vaccine remains a major objective in Salmonella research, the realization of which would have a profound impact on global food safety and public health.

Recent studies have explored the combined use of bacteriophages and probiotics as a synergistic strategy to enhance anti-Salmonella efficacy while mitigating limitations associated with single-modality treatments. In this context, Lactobacillus plantarum with phage resistance was cultured in 2019, and the LP^+PR strain significantly inhibited the adhesion and invasion abilities of INT-407 cells (p < 0.05) (Nagarajan et al., 2019). In 2022, Naveen isolated the lytic Salmonella phage NINP13076 and took it orally for five days, verifying that the oral phage did not damage the probiotic intestinal microbiota (Wang et al., 2022). In the same year, Xinwu investigated a combined strategy using a phage cocktail and the probiotic Lactobacillus reuteri to control S. Typhimurium. In vitro assays showed that the combination effectively eliminated S. Typhimurium, indicating a synergistic antibacterial effect. The expression of the inflammatory factors IL-6, IL-1β and TNF-α decreases significantly (Kumar et al., 2022). All the above findings prove the positive effects of phages combined with probiotics.

Beyond their use as standalone interventions, phages have also been investigated for their compatibility with vaccination strategies, particularly to assess whether phage administration interferes with vaccine-induced immunity. In addition, Kimminau verified through in vitro experiments on broiler chickens that dietary phages do not interfere with the colonization or protection of Salmonella live vaccines (Kimminau et al., 2022). To determine the adaptive immune response to S. Enteritidis, an oral vaccine was administered after exposure to the phage. The results showed that vaccination with a live Enteritidis phage type 4 vaccine could prevent early systemic invasion of S. typhi and S. infantis (Springer et al., 2021).

In addition to phage-based combinations, probiotics have also been explored as adjuncts to vaccination strategies to enhance host immune responses and improve protective efficacy against Salmonella infection. Graham attempted to use probiotics combined with a recombinant attenuated Salmonella live vaccine for verification. The results show that probiotics can improve the bactericidal activity of innate effector cells in whole blood and that the live vaccine RASV can stimulate the bactericidal activity of probiotics, indicating the feasibility of combined therapy (Redweik et al., 2020). Peter J. added a probiotic to the daily drinking water of chickens and injected it intramuscularly at ten weeks of age as a live aro-A deletion mutant vaccine. The vaccine helps limit excretion at sexual maturity and reduces susceptibility to subsequent challenges. The use of probiotics enhances the protective capabilities of vaccines (Groves et al., 2021).