Antibacterial efficacy of core-shell nanostructures encapsulating gentamicin against an in vivo intracellular  Salmonella model

Ashish Ranjan¹, Nikorn Pothayee^2,3, Mohammed N Seleem², Ronald D Tyler Jr⁴, Bonnie Brenseke⁴, Nammalwar Sriranganathan^2,4, Judy S Riffle^2,3, Ramanathan Kasimanickam¹

¹Department of Large Animal Clinical Sciences, ²Institute for Critical Technology and Applied Science, ³Macromolecules and Interfaces Institute, ⁴Department of Biomedical Sciences and Pathobiology, Virginia Polytechnic Institute and State University, Blacksburg, VA

Abstract: Pluronic based core-shell nanostructures encapsulating gentamicin were designed in this study. Block copolymers of (PAA^–+Na-b-(PEO-b-PPO-b-PEO)-b-PAA^{– +}Na) were blended with PAA^– Na⁺ and complexed with the polycationic antibiotic gentamicin to form nanostructures. Synthesized nanostructures had a hydrodynamic diameter of 210 nm, zeta potentials of –0.7 (±0.2), and incorporated ~20% by weight of gentamicin. Nanostructures upon co-incubation with J774A.1 macrophage cells showed no adverse toxicity in vitro. Nanostructures administered in vivo either at multiple dosage of 5 µg g^–1 or single dosage of 15 µg g^–1 in AJ-646 mice infected with Salmonella resulted in significant reduction of viable bacteria in the liver and spleen. Histopathological evaluation for concentration-dependent toxicity at a dosage of 15 µg g^–1 revealed mineralized deposits in 50% kidney tissues of free gentamicin-treated mice which in contrast was absent in nanostructure-treated mice. Thus, encapsulation of gentamicin in nanostructures may reduce toxicity and improve in vivo bacterial clearance.

Keywords: gentamicin, core-shell nanostructures, Salmonella