The review followed the PRISMA-ScR reporting guidelines and was registered in advance in the OSF database. Searches of PubMed, Scopus and Web of Science conducted in November 2025 returned 5,053 records, which were reduced to 2,801 after duplicate removal and screened down to 93 potentially relevant articles. After applying predefined inclusion and exclusion criteria, 79 studies were excluded, most often because they examined nanoparticles paired with metals or other non-antibiotic materials rather than antibiotics. A complementary manual search of Google Scholar and the reference lists of relevant articles added 10 further eligible studies, bringing the final tally to 24 articles published between 2016 and 2025.

The motivation for combining nanoparticles with antibiotics lies in the nature of antimicrobial resistance itself. Bacteria are not static targets: they can alter their surface charge in response to a biomaterial, becoming more positive on negatively charged surfaces and thereby repelling cationic drugs such as vancomycin. The same electrostatic adaptations help bacteria adhere to surfaces and build biofilms, structured communities reinforced by positively charged secretions that act as bridges between anionic components of the cell surface. These mechanisms make biofilm-associated infections among the most difficult to treat and contribute to the tolerance that conventional antibiotics increasingly fail to overcome.

Zinc oxide nanoparticles attack bacteria through several routes at once. Their tunable size and morphology give them a high surface area-to-volume ratio, favoring close contact with bacterial cell walls. They generate reactive oxygen species, release zinc ions, destabilize membranes, interfere with metabolic pathways and disrupt active transport systems. Antibiotics, by contrast, target specific essential processes such as DNA replication, protein synthesis or cell wall assembly. The review’s authors propose that the nanoparticles may soften bacterial defenses, increasing membrane permeability and possibly inhibiting efflux pumps, so that antibiotics reach their targets more effectively. They caution, however, that these mechanisms were often inferred from antimicrobial outcomes or prior literature rather than directly demonstrated in the combination studies.

How the two agents were combined varied widely. Thirteen of the 24 studies used simple physical mixtures, co-administering nanoparticles and antibiotics without prior integration. Only three explored chemical conjugation, four used encapsulated systems embedding both agents in polymer carriers such as chitosan, and four loaded antibiotics onto the nanoparticles by adsorption or within mesoporous structures. Fluoroquinolones were the most frequently studied class, appearing in 12 studies, followed by beta-lactams. Gram-negative bacteria dominated the test organisms, accounting for roughly 63 percent of microbial species examined, reflecting interest in overcoming the structural barriers and multidrug resistance typical of that group.

Some of the more engineered systems produced striking results. In one study, mesoporous zinc oxide nanoparticles carrying piperacillin-tazobactam or ciprofloxacin were tested against Escherichia coli and multidrug-resistant Pseudomonas aeruginosa; neither agent alone inhibited Pseudomonas growth, but the combination achieved complete bactericidal activity within 24 hours of growth-kinetics monitoring. Another team coated nanoparticles with gentamicin and chloramphenicol to treat multidrug-resistant E. coli from bovine mastitis and reported a 312 percent increase in antimicrobial efficacy compared with nanoparticles alone for the dual-coated formulation. In wound models, a PEG-coated, ciprofloxacin-loaded system accelerated healing by 20 percent and eradicated infection within two days, while a nanofiber wound dressing combining amikacin and cefepime with zinc oxide nanoparticles in a chitosan, polyvinylpyrrolidone and gelatin matrix led to complete skin regeneration and new hair growth in treated animals within 14 days.

The review’s authors applied a critical lens to the word “synergy” itself. Eight studies in total used quantitative interaction analyses such as the fractional inhibitory concentration index or time-kill assays, the methods generally required to demonstrate true pharmacological synergy, and only five of those fell among the physical-mixture studies. Many others reported reduced minimum inhibitory or bactericidal concentrations, larger inhibition zones, or antibiofilm effects without these standards, and several relied solely on statistical significance. The review therefore classified much of the evidence as enhanced antimicrobial activity or potential synergy rather than definitively confirmed synergy, urging future work to adopt checkerboard assays, time-kill curves and resistant clinical isolates.

Biofilm data, though limited, offered some of the most clinically relevant findings. Ten of the 24 studies included biofilm models, typically using 96-well plates with crystal violet staining to measure biofilm biomass. Studies reported both prevention of biofilm formation and disruption of established biofilms, with mechanisms proposed including reactive oxygen species damaging the extracellular matrix, reduced bacterial surface hydrophobicity impairing adhesion, and downregulation of biofilm-regulating genes. One study of physical mixtures across six antibiotic classes found that even the weakest nanoparticle-antibiotic combination still reduced Staphylococcus aureus biofilm formation by 60 percent. Because many persistent infections involve biofilms rather than free-floating bacteria, the reviewers argue that standardized antibiofilm methodologies are essential before these systems can be judged therapeutically meaningful.

Safety data emerged as the field’s most conspicuous gap. Fourteen of the 24 studies included no toxicity assessment at all. Among those that did, five used in vitro cytotoxicity assays, five conducted in vivo investigations and one used the Hen’s Egg Test on the chorioallantoic membrane. Encouragingly, some engineered formulations appeared less toxic than the bare nanoparticles: PEG coating reduced hemolysis of human red blood cells from 5 to 7 percent for uncoated particles to no significant hemolysis, and chitosan encapsulation improved cytocompatibility in kidney cell lines, with cell viability reaching 90 to 95 percent even at the highest concentrations tested. A risk-of-bias assessment of the five in vivo studies using SYRCLE’s tool found predominantly unclear judgments, driven by incomplete reporting of randomization, allocation concealment and blinding, underscoring weak methodological transparency in the preclinical literature.

The reviewers conclude that zinc oxide nanoparticle-antibiotic systems represent a genuinely promising strategy against resistant bacteria, but that translation will demand far more than microbiological potency. Future studies must provide complete physicochemical characterization, including size distribution, surface charge and aggregation state; establish whether the microgram-per-milliliter concentrations effective in vitro can be safely achieved and maintained at infection sites; and address pharmacokinetics, biodistribution, organ accumulation and long-term toxicity. Manufacturing reproducibility, batch-to-batch consistency, scale-up feasibility and regulatory-grade quality control also remain largely unaddressed. Until those gaps close, nanoparticle-mediated synergy will remain a laboratory concept rather than a clinical weapon in the fight against antimicrobial resistance.

Subject of Research: Combining zinc oxide nanoparticles with antibiotics to enhance antimicrobial activity against resistant bacteria

Article Title: Synergistic effect of zinc oxide nanoparticles and antibiotics: a strategy to combat bacterial resistance

Article References: Salto, M. P., de Freitas, N. G., Fanhani, F. C., Ferreira, L. M., Junior, J. A. O., Lemaire, L., dos Santos, J. L., & Chiavacci, L. A. (2026). Synergistic effect of zinc oxide nanoparticles and antibiotics: a strategy to combat bacterial resistance. Advanced Biotechnology, 4(4), Article 44. https://doi.org/10.1007/s44307-026-00137-4

Image Credits: AI Generated

DOI: 10.1007/s44307-026-00137-4

Keywords: antimicrobial resistance, zinc oxide nanoparticles, antibiotics, synergy, biofilms, nanotechnology, scoping review, drug delivery, toxicity, Gram-negative bacteria, fluoroquinolones, reactive oxygen species