Background Multidrug-resistant Acinetobacter baumannii is an important healthcare-associated pathogen, necessitating therapeutic strategies. This study evaluates the antibacterial efficacy of imipenem-encapsulated chitosan/hydroxypropyl methylcellulose phthalate (Imp-Chi) nanoparticles against clinical A. baumannii isolates. Methods A. baumannii clinical isolates (n = 105) from hospitalized patients were characterized for antibiotic resistance via broth microdilution and classified as MDR, XDR, or PDR. An exploratory PCR screen was performed for the selected AmpC-family genes mox, cit, and dha. Imp-Chi nanoparticles were synthesized via ionic gelation, characterized for size, zeta potential, morphology, encapsulation efficiency, and drug release. Antibacterial activity was assessed via MIC assays against the A. baumannii clinical isolates. Recoverable bacterial burden in extracellular, cell-associated, and intracellular fractions of A549 and NCI-H292 infection models was quantified, alongside reactive oxygen species (ROS) and cytotoxicity assessments using MTT and LDH assays. Results Isolates exhibited high resistance to β-lactams (97.1–99.0%), carbapenems (94.3–98.1%), and aminoglycosides (92.4–96.2%), with 77.1% classified as PDR. No significant association was observed between the selected AmpC-family genes and resistance phenotypes (p > 0.05). Imp-Chi nanoparticles (291.3 nm, + 34.9 mV; spherical morphology with smooth surfaces) demonstrated optimal encapsulation efficiency (1.5 µg imipenem) and sustained drug release (70% over 10 h). MICs of Imp-Chi nanoparticles were significantly lower than free imipenem (p < 0.0001; ~0.31-fold reduction); while fractional inhibitory concentration index values clustered around 1.0, supporting an additive or near-additive rather than synergistic interaction, and the nanoparticles also reduced recoverable bacterial CFU across extracellular and host-cell-associated fractions in lung epithelial infection models in vitro. ROS levels in A. baumannii-infected cells decreased to near-baseline levels following Imp-Chi treatment (p < 0.0001). MTT and LDH readouts suggested limited cytotoxicity-associated effects at 100–200 µg/mL and concentration-dependent effects at higher concentrations, with apparent MTT-derived IC₅₀ values of approximately 740 µg/mL; however, nanoparticle-related assay interference and carrier-specific effects were not independently excluded. Conclusions Imp-Chi nanoparticles reduced imipenem MICs through additive or near-additive antibacterial contributions and may also provide formulation-related delivery advantages, while reducing bacterial burden in lung epithelial infection models and being associated with lower infection-associated ROS levels in vitro. Clinical trial number Not applicable.

Antibacterial activity of imipenem-encapsulated chitosan/HPMCP nanoparticles against clinical Acinetobacter baumannii isolates

期刊论文
出版模式：

开放获取
发表日期：

2026年7月25日

查看全文

Sajad Alizadeh,
Majid Baseri Salehi,
Nima Bahador

摘要

Background

Multidrug-resistant Acinetobacter baumannii is an important healthcare-associated pathogen, necessitating therapeutic strategies. This study evaluates the antibacterial efficacy of imipenem-encapsulated chitosan/hydroxypropyl methylcellulose phthalate (Imp-Chi) nanoparticles against clinical A. baumannii isolates.

Methods

A. baumannii clinical isolates (n = 105) from hospitalized patients were characterized for antibiotic resistance via broth microdilution and classified as MDR, XDR, or PDR. An exploratory PCR screen was performed for the selected AmpC-family genes mox, cit, and dha. Imp-Chi nanoparticles were synthesized via ionic gelation, characterized for size, zeta potential, morphology, encapsulation efficiency, and drug release. Antibacterial activity was assessed via MIC assays against the A. baumannii clinical isolates. Recoverable bacterial burden in extracellular, cell-associated, and intracellular fractions of A549 and NCI-H292 infection models was quantified, alongside reactive oxygen species (ROS) and cytotoxicity assessments using MTT and LDH assays.

Results

Isolates exhibited high resistance to β-lactams (97.1–99.0%), carbapenems (94.3–98.1%), and aminoglycosides (92.4–96.2%), with 77.1% classified as PDR. No significant association was observed between the selected AmpC-family genes and resistance phenotypes (p > 0.05). Imp-Chi nanoparticles (291.3 nm, + 34.9 mV; spherical morphology with smooth surfaces) demonstrated optimal encapsulation efficiency (1.5 µg imipenem) and sustained drug release (70% over 10 h). MICs of Imp-Chi nanoparticles were significantly lower than free imipenem (p < 0.0001; ~0.31-fold reduction); while fractional inhibitory concentration index values clustered around 1.0, supporting an additive or near-additive rather than synergistic interaction, and the nanoparticles also reduced recoverable bacterial CFU across extracellular and host-cell-associated fractions in lung epithelial infection models in vitro. ROS levels in A. baumannii-infected cells decreased to near-baseline levels following Imp-Chi treatment (p < 0.0001). MTT and LDH readouts suggested limited cytotoxicity-associated effects at 100–200 µg/mL and concentration-dependent effects at higher concentrations, with apparent MTT-derived IC₅₀ values of approximately 740 µg/mL; however, nanoparticle-related assay interference and carrier-specific effects were not independently excluded.

Conclusions

Imp-Chi nanoparticles reduced imipenem MICs through additive or near-additive antibacterial contributions and may also provide formulation-related delivery advantages, while reducing bacterial burden in lung epithelial infection models and being associated with lower infection-associated ROS levels in vitro.

Clinical trial number

Not applicable.