The rise of infections caused by multidrug-resistant (MDR) pathogens has compromised the efficacy of conventional antibiotic treatments, posing a global threat to public health, food safety, and modern medicine (Samtiya et al., 2022; Ahmed et al., 2024; Naghavi et al., 2024). As antimicrobial resistance (AMR) spreads across both pathogenic and commensal bacterial populations, the urgency to discover alternative or complementary strategies to traditional treatment has intensified (Bassetti et al., 2009; Ahmed et al., 2024). In parallel with the increasing adoption of stewardship policies and regulatory restrictions on antibiotic use in clinical, agricultural, and food-production settings, non-antibiotic approaches are gaining renewed attention.

One such approach involves the use of bacteriophages (phages)—viruses that specifically infect bacteria. Since their discovery over a century ago, phages have been explored as therapeutic agents due to their high specificity, minimal disruption of the host microbiota, and capacity for evolutionary adaptation. However, following the introduction of penicillin and the inconsistent outcomes of early phage applications, interest in phage therapy declined in much of the Western world (Górski et al., 2019). Only a few facilities in Eastern and Central Europe studied phage therapeutic potential and decided to use them either as Over-the-Counter (OTC) medications or as an experimental therapy (Parfitt, 2005; Żaczek et al., 2022). However, interest in phage therapy has recently resurged in the West due to the AMR crisis and advances in genomics, synthetic biology, and microbiome science. While phage therapy offers unique advantages, such as high specificity, minimal disruption of the host microbiota, and evolutionary adaptability, it has limitations when used in isolation. These include narrow host range, rapid development of bacterial resistance to phages, and challenges associated with phage delivery and pharmacokinetics (Labrie et al., 2010; Lin et al., 2022; Nang et al., 2023). To overcome these limitations, it is recommended to use phage cocktails or pair phage preparations with other antimicrobials (Wright et al., 2021; Morris et al., 2025). To date, phage–antibiotic combinations have been the most extensively studied, demonstrating enhanced bacterial killing and reduced emergence of resistance to either agent (Loganathan et al., 2024; Qin et al., 2024; Morris et al., 2025). However, widespread efforts to limit antibiotic use, together with regulatory bans in certain sectors and concerns regarding toxicity, allergies, and environmental impact, restrict the long-term applicability of antibiotic-based combinations (Tang et al., 2017; Kahn et al., 2019). These limitations have stimulated growing interest in pairing bacteriophages with non-antibiotic antimicrobial compounds. Several studies have demonstrated that phage synergy with non-antibiotic antimicrobials can improve bacterial eradication, delay or prevent resistance development, and enhance biofilm penetration. Those may help through, e.g., increased efficacy of phage adsorption, interference of bacterial stress responses (Philippe et al., 2020; Lin et al., 2024), alteration of bacterial membrane integrity or cell wall charge (Alisigwe et al., 2025), and creation of oxidative environments that both impair bacterial defense systems and stabilize phage particles (Philippe et al., 2020; Alisigwe et al., 2025; Wdowiak et al., 2025b). These proposed synergy mechanisms are shown in Figure 1.

In this review, we examine the synergistic interactions between bacteriophages and selected antimicrobial compounds, considering mechanistic principles, practical limitations, and translational potential across clinical, food-safety, and agricultural contexts.

Bacteriophage therapy has demonstrated clear therapeutic potential, with numerous case studies reporting successful treatment of pneumonia, sepsis, skin, and urinary tract infections caused by antibiotic-resistant pathogens (Valente et al., 2021; Żaczek et al., 2022). Despite these advantages, phage therapy faces several intrinsic and context-dependent limitations that restrict its widespread and predictable application. One of the most significant constraints is the narrow host range of most bacteriophages. Unlike broad-spectrum antibiotics, phages typically infect only specific bacterial species or even individual strains. This specificity arises from precise interactions between phage receptor-binding proteins and bacterial surface structures, meaning that even minor alterations in receptors can abolish phage infectivity (Hyman and Abedon, 2010; Holtappels et al., 2023; Chung et al., 2023). While high specificity is beneficial for preserving the commensal microbiota, it complicates clinical use, as pathogens must often be isolated and characterized prior to treatment. This requirement can delay therapy, particularly in acute or life-threatening infections, and limits the immediate applicability of standardized phage preparations.

Another major limitation is the emergence of bacterial resistance to bacteriophages. Bacteria may evade phage infection through diverse mechanisms, including receptor modification or loss, CRISPR–Cas systems, restriction–modification systems, and abortive infection pathways (Figure 2) (Oechslin, 2018; Oromí-Bosch et al., 2023). Although it has been shown that phages coevolve with their hosts and that new phages can be easily isolated from the environment, the emergence of phage resistance remains a major concern (Koskella and Brockhurst, 2014; Jurczak-Kurek et al., 2016; Batinovic et al., 2019; Egido et al., 2022). While the use of phage cocktails can slow down the emergence of phage-resistant bacteria, they increase the complexity of the therapeutic and pose a regulatory burden on the use of phage-based products (Oromí-Bosch et al., 2023; Faltus, 2024). On the other hand, many resistance mechanisms impose physiological or fitness costs on bacteria, altering surface structures, metabolic activity, or stress responses. These trade-offs may create vulnerabilities that can potentially be exploited by complementary antimicrobial agents. Beyond phage–bacteria interactions, host-related factors also influence phage therapy outcomes. Phages introduced into the human or animal body can be recognized and neutralized by the immune system, particularly after repeated administrations. Components of both innate and adaptive immunity, like macrophages, complement proteins, and phage-specific antibodies, may reduce the administered phage titer before it reaches its bacterial targets (Górski et al., 2012; Podlacha et al., 2021; Łusiak-Szelachowska et al., 2022; Champagne-Jorgensen et al., 2023; Gembara and Dąbrowska, 2024). In addition, the pharmacokinetics and pharmacodynamics of phages are more complex than those of conventional antimicrobials, as phage concentrations at infection sites depend on bacterial titer, replication dynamics, route of administration, and host immune responses (Chatain-Ly, 2014; Nang et al., 2023). Effective phage delivery can be further hindered by physical and environmental barriers. Biofilms, intracellular niches, mucus layers, poorly vascularized tissues, and complex matrices such as food or plant surfaces can limit phage access to bacterial cells and reduce therapeutic efficacy (Barr et al., 2015; Bichet et al., 2021; Chang et al., 2022). Although phages can, in some contexts, penetrate biofilms or interact with eukaryotic cells, their activity in such environments is often inconsistent and highly context-dependent.

Collectively, these limitations highlight that the success of phage therapy is governed not only by phage–host specificity, but also by bacterial physiology, resistance dynamics, host immunity, and environmental constraints. These challenges have driven growing interest in rational combination strategies designed to support phage activity, improve delivery, and suppress resistance, rather than relying on phages as stand-alone antimicrobials.

Combination therapies pairing bacteriophages with antibiotics, commonly referred to as phage–antibiotic synergy (PAS), have been extensively investigated as a strategy to enhance antibacterial efficacy and limit the development of resistance. Numerous in vitro and in vivo studies have demonstrated that carefully selected phage–antibiotic combinations can outperform either agent alone, leading to improved bacterial removal and, in some cases, halt the emergence of resistant subpopulations (Gu Liu et al., 2020; Zhao et al., 2024; Loganathan et al., 2024). Mechanistically, PAS arises through several processes. Antibiotics that interfere with bacterial cell wall synthesis or DNA replication can induce physiological changes, such as filamentation, altered metabolism, or stress responses, that increase susceptibility to phage infection and replication (O’Rourke et al., 2020; Lee et al., 2025). In some systems, sublethal antibiotic concentrations have been shown to enhance phage adsorption, accelerate intracellular phage production, or increase burst size, amplifying antibacterial effect (Comeau et al., 2007; Knezevic et al., 2021; Loganathan et al., 2024). Conversely, phage-induced bacterial lysis may increase antibiotic penetration or expose previously inaccessible subpopulations of bacteria (De Soir et al., 2025). Importantly, PAS can also influence resistance dynamics. Antibiotic pressure may limit the emergence of phage-resistant mutants, while phage presence in the culture can suppress antibiotic-resistant bacterial subpopulations or impose fitness costs that restore antibiotic sensitivity (Oechslin, 2018; Qin et al., 2024). These effects highlight that synergy is not merely additive, but is based on complex interactions between bacterial physiology, stress responses, and evolutionary trade-offs (Mangalea and Duerkop, 2020; Zhang and Ahn, 2025).

Despite these advantages, the clinical and industrial applicability of PAS is limited by efforts to reduce the use of antibiotics. Global antibiotic stewardship programs, regulatory restrictions in agriculture and food production, and concerns about toxicity, allergic reactions, and environmental dissemination limit the feasibility of antibiotic-based combination strategies (Tang et al., 2017; Kahn et al., 2019).

Therefore, rather than being seen as a universal solution, PAS provides a valuable conceptual framework for understanding how other antimicrobial agents can modulate phage activity. The mechanistic principles underlying PAS are not exclusive to antibiotics. These same principles can be observed when pairing phages with non-antibiotic antimicrobial compounds, enabling the exploration of alternative phage-based combination strategies (Lin et al., 2024; Wdowiak et al., 2025a; Janesomboon et al., 2025). Published reports show promising results for some of those combinations. However, they touch on the possible limitations or disadvantages as well. Explored combinations of phages with various antimicrobials for potential use in agriculture, food industry, and healthcare are presented in Figure 3.

Plant-derived antimicrobial compounds, particularly essential oils (EO’s), have attracted increasing attention as potential adjuvants for bacteriophage-based antimicrobial formulations. Essential oils are complex mixtures of volatile secondary metabolites, including terpenes, phenolics, and aldehydes, many of which exhibit broad-spectrum antibacterial activity (Bakkali et al., 2008; de Groot and Schmidt, 2016). Their antimicrobial effects include disruption of bacterial cell wall or outer membrane integrity, interference with metabolism, and induction of oxidative stress responses (Wang et al., 2020; Aljaafari et al., 2021). In the context of phage therapy, these properties are of particular interest because they target bacterial features that are directly relevant to phage infection. Alterations in cell wall and membrane structure, surface charge, and permeability can influence phage adsorption efficiency, while stress-induced physiological changes may affect intracellular phage replication dynamics (Addo et al., 2024; Leprince and Mahillon, 2023; Bruce et al., 2026). In addition, several essential oils and plant-derived compounds have been shown to weaken biofilm structure or increase bacterial susceptibility within biofilms, thereby facilitating phage biofilm penetration (Reichling, 2020; Mathlouthi et al., 2021; Rossi et al., 2022; Yang et al., 2025). Unlike antibiotics, EOs are commonly used in food preservation and agriculture and have a well-established regulatory status and high public acceptance (Matté et al., 2023; Ivanova et al., 2025). The research on the prospective use of phage-EOs combinations focuses mainly on food safety and agriculture (Matté et al., 2023; Stevanović et al., 2018). However, the complexity and variability of essential oil composition, as well as their potential to inactivate phages at higher concentrations, necessitate careful evaluation of synergistic interactions on a case-by-case basis (Sheng et al., 2016; Afshari and Rahimmalek, 2018; Kamarasu et al., 2025).

Multiple studies have examined the combined application of bacteriophages with essential oils or their individual components against both Gram-positive and Gram-negative bacteria (Table 1). Across diverse experimental systems, these combinations have generally resulted in greater bacterial reduction than either phages or essential oils alone, although the degree of synergy varied depending on bacterial species, phage type, and experimental conditions (Ghosh et al., 2016; Fokas et al., 2025). Reported synergistic effects were most frequently observed at subinhibitory concentrations, where membrane disruption and stress induction appeared to enhance phage adsorption and replication without compromising phage viability (Ebani and Mancianti, 2020; Kim et al., 2024; Fokas et al., 2025). Several studies demonstrated improved phage efficacy against bacterial biofilms following essential oil exposure, suggesting that partial biofilm disruption or increased bacterial cell wall permeability facilitated phage penetration (Han et al., 2024; Kao Godínez et al., 2025). In some cases, combined treatments resulted in significantly delayed emergence of phage-resistant bacteria (Maung et al., 2024; Elafify et al., 2025). Key findings and methodological parameters of published phage–essential oil synergy studies are summarized in Table 1.

Despite these promising findings, important limitations remain. Essential oils exhibit substantial variability in chemical composition depending on plant species, extraction method, and formulation, complicating reproducibility and standardization (Afshari and Rahimmalek, 2018; Talebi et al., 2024). Concentration-dependent effects should not be overlooked, as doses sufficient to damage bacterial membranes may also inactivate phage particles or reduce their stability (Sheng et al., 2016; Kamarasu et al., 2025). Mechanistic insights are often inferred rather than directly demonstrated, underscoring the need for integrated approaches combining microbiological, biophysical, and omics-based analyses (Fokas et al., 2025). Addressing these gaps will be essential for determining whether essential oils can serve as reliable and scalable adjuvants to phage-based antimicrobial strategies.

Bacteriocins are ribosomally synthesized antimicrobial peptides or proteins produced by bacteria that exhibit potent and often narrow-spectrum activity against closely related species (EFSA Panel on Food Additives et al., 2017; Rendueles et al., 2022). Their antibacterial effects commonly involve pore formation in the cytoplasmic membrane, inhibition of cell wall biosynthesis, or interference with essential intracellular processes (Vasilchenko and Valyshev, 2019; Telhig et al., 2020; Martínez et al., 2020; Rendueles et al., 2022). Due to their defined molecular targets and proteinaceous nature, bacteriocins have been explored as alternatives or complements to conventional antibiotics in both clinical and food-related applications (Rendueles et al., 2022; Leprince and Mahillon, 2023; Fokas et al., 2025). From a phage-therapy perspective, bacteriocins are seen as promising combination partners as their mechanisms of action overlap. Unlike essential oils, bacteriocins are chemically well-defined and can be produced using standardized methods, improving reproducibility and dosing precision. However, their relatively narrow spectrum of activity and susceptibility to proteolytic degradation present challenges for therapeutic deployment, particularly in vivo.

Several studies have investigated the combined use of bacteriophages and bacteriocins against clinically and industrially relevant bacterial pathogens, including Staphylococcus aureus, Listeria monocytogenes, and Salmonella sp. (Table 2). Research on phage–bacteriocin synergy has focused primarily on L. monocytogenes, with nisin as the most studied compound, often combined with commercial phage products such as P100 or LMP-102 (Rendueles et al., 2022). Subsequent studies demonstrated enhanced reductions in bacterial load across diverse food matrices, including fruit, fish, meat, and dairy products, frequently outperforming individual treatments and chemical sanitizers (Dykes and Moorhead, 2002; Leverentz et al., 2003; Soni et al., 2014; Figueiredo and Almeida, 2017; Lewis et al., 2019; Ibarra-Sánchez et al., 2018; Baños et al., 2016a; Rodríguez-Rubio et al., 2015; Komora et al., 2020) Similar synergistic effects have been reported against S. aureus, where combinations of nisin with phages or phage-derived endolysins showed enhanced efficacy in milk and broth, particularly at sub-optimal concentrations, despite matrix-dependent outcomes, and without cross-resistance between phages and bacteriocins (Martínez et al., 2020; Gembara and Dąbrowska, 2024; Duc et al., 2020a; Kim et al., 2019). Beyond these pathogens, phage–bacteriocin combinations improved control of Salmonella sp. in food and biofilm models and achieved complete eradication of Clostridium perfringens in co-culture (Wang et al., 2017; Yüksel et al., 2018; Heo et al., 2018). A detailed summary of bacterial targets, phages, bacteriocins, experimental conditions, and outcomes is provided in Table 2.

Overall, available evidence suggests that synergy between bacteriophages and bacteriocins (similarly to phage-EOs synergy) is most commonly associated with membrane and cell wall perturbations that enhance phage adsorption and genome delivery, as well as through stress-induced physiological changes that favor phage replication (Vasilchenko and Valyshev, 2019; Telhig et al., 2020; Martínez et al., 2020; Rendueles et al., 2022). Nevertheless, several limitations constrain the broader application. Many bacteriocins display narrow target specificity, which may restrict their utility against diverse bacterial populations. Proteolytic instability, potential immunogenicity, and reduced activity in complex biological matrices are additional challenges, particularly for systemic applications. Moreover, most studies have been conducted in vitro, with limited assessment of pharmacokinetics, safety, and in vivo long-term resistance dynamics. Addressing these knowledge gaps will be essential for determining whether bacteriocins can serve as adjuvants to phage-based antimicrobial strategies.

Nanoparticles (NPs), including metallic, metal oxide, and polymer-based nanomaterials, have emerged as promising antimicrobial agents due to their high surface area, tunable physicochemical properties, and diverse mechanisms of antibacterial action. Antimicrobial nanoparticles, such as silver, gold, zinc oxide, copper oxide, and chitosan-based materials, exhibit bactericidal effects by disrupting membranes, generating reactive oxygen species, interfering with metabolic pathways, and damaging nucleic acids and proteins.

In the context of phage therapy, nanoparticles are seen as promising not only as direct antimicrobial agents but also as enhancers of phage activity or delivery systems. Nanoparticles can both alter bacterial surface properties, allowing for more efficient phage adsorption, or act as carriers that protect phages from unfavorable environmental conditions. A growing number of studies have explored the combined use of bacteriophages with antimicrobial nanoparticles against a range of bacterial pathogens, including E. coli, Pseudomonas aeruginosa, and S. aureus (Table 3). Sub-MIC concentrations of biogenic AgNPs combined with Salmonella phages (ZCSE2, ZCSE6, P22) significantly enhanced bacterial inhibition in broth and food models without phage inactivation or increased cytotoxicity, even at low MOIs, and consistently outperformed individual treatments (Abdelsattar et al., 2021; 2022; Makky et al., 2023; Wdowiak et al., 2025a). Genetic modification of phages to display AgNP-binding peptides further improved antibiofilm efficacy at high phage titers while maintaining stability and safety for eukaryotic cells (Szymczak et al., 2024; Szymczak and Golec, 2024a). Comparable synergistic effects were observed against S. aureus, including biofilm dispersal and reduced survival rates, as well as with phage-mimicking silver–gold nanostructures active against MRSA (Hopf et al., 2019; Manoharadas et al., 2021; Wdowiak et al., 2025a). Although AgNPs dominate current research, synergy has also been demonstrated with gold, copper, and zinc nanoparticles (Hopf et al., 2019; Peng et al., 2020; Alipour-Khezri et al., 2024; Zhang et al., 2024a).

A detailed overview of bacterial targets, phages, nanoparticle types, physicochemical properties, experimental conditions, and observed effects is provided in Table 3.

Taken together, existing studies indicate that synergy between bacteriophages and nanoparticles most commonly arises from indirect enhancement of phage activity rather than simple additive antibacterial effects. In some applications, nanoparticles have also been used as carriers or protective matrices to improve phage stability and persistence under environmental stress (Peng et al., 2020).

Despite these promising results, significant challenges limit the translational potential. Many NPs exhibit dose-dependent cytotoxicity toward eukaryotic cells and may accumulate in environmental or biological systems, raising safety and ecological concerns (Xiong et al., 2022; Islam, 2025). Regulatory frameworks governing nanoparticle use in health, food industry, or agriculture are not yet fully defined, while large-scale manufacturing with consistent quality and reproducibility presents an additional challenge (Wang et al., 2024; Wdowiak et al., 2025a). Future research should prioritize systematic optimization of nanoparticle properties, rigorous safety assessment, and mechanistic studies that distinguish true synergy from concentration-dependent additive effects.

In addition to essential oils, bacteriocins, and nanoparticles, a range of other non-antibiotic compounds have been investigated as adjuncts to bacteriophage-based antimicrobial strategies. Although these agents differ substantially in origin and primary function, they share the capacity to modulate bacterial physiology, alter environmental conditions, or improve phage stability and delivery. This section summarizes selected examples that do not fall into the preceding categories but provide insight into additional mechanisms by which phage efficacy may be enhanced.

The growing burden of MDR bacterial infections has renewed interest in bacteriophage-based antimicrobials as alternatives or complements to conventional antibiotics. However, the efficacy of phage therapy as a stand-alone approach is constrained by factors including narrow host range, resistance development, delivery challenges, and context-dependent activity in complex biological and environmental matrices. These limitations have driven increasing attention toward combination strategies designed to enhance phage performance.

The evidence summarized in this review demonstrates that non-antibiotic antimicrobial compounds can act as effective phage adjuvants across diverse application areas, including clinical therapy, food safety, and agriculture. Essential oils, bacteriocins, nanoparticles, and other agents have been shown to enhance phage efficacy through multiple, often overlapping, mechanisms. These include: destabilization of bacterial cell walls and outer membrane integrity, which facilitates phage adsorption; modulation of bacterial stress responses that influence phage replication dynamics; disruption of biofilm structure, which facilitates phage penetration; and improvement of phage stability or delivery under adverse environmental conditions. Importantly, in several systems, these effects have also been shown to delay the emergence of phage-resistant bacterial clones, highlighting the potential of combination strategies to constrain the phage-bacteria arms race.

At the same time, the studies show that phage–adjuvant synergy is highly context-dependent. Outcomes vary depending on bacterial species and strain, phage type, compound class, concentration, treatment time, and order of administration. In some cases, non-antibiotic compounds reduced phage stability or infectivity at higher concentrations, emphasizing the need for careful optimization and mechanistic compatibility. Moreover, to date, there is limited data from in vivo models, as most of the studies discussed in this review focused on in vitro experiments. Therefore, the translation of these findings into practice remains difficult to assess.

Future research should focus on mechanistic approaches to phage-based combination therapy. Systematic studies on dose–response relationships, timing, and resistance are needed to identify actual synergistic effects from additive or antagonistic ones. Combining microbiological tests with imaging, biophysical analysis, and omics methods will be crucial to understanding the molecular and physiological basis of these synergies. Additionally, more attention should be paid to safety, regulatory issues, and ecological impacts, especially for nanoparticle systems and environmental applications.

In conclusion, non-antibiotic antimicrobial compounds represent a diverse and promising tool for enhancing bacteriophage efficacy across multiple sectors. However, based on the current data, these agents should be viewed as context-specific modulators of phage activity, rather than serving as universal solutions. Continued interdisciplinary efforts will be critical to translate phage–adjuvant combination strategies from experimental proof-of-concept studies into robust, safe, and scalable antimicrobial interventions.