Enhancing Gentamicin Antibacterial Activity by Co-Encapsulation with Thymoquinone in Liposomal Formulation

Gentamicin (GEN) is a broad-spectrum antibiotic that cannot be prescribed freely because of its toxicity. Thymoquinone (THQ), a phytochemical, has antibacterial, antioxidant, and toxicity-reducing properties. However, its hydrophobicity and light sensitivity make it challenging to utilize. This incited the idea of co-encapsulating GEN and THQ in liposomes (Lipo-GEN-THQ).

Lipo-GEN-THQ were characterized using the zeta-potential, dynamic light scattering, Fourier transform infrared spectroscopy, and transmission electron microscope (TEM). The liposomes' stability was evaluated under different storage and biological conditions. Lipo-GEN-THQ's efficacy was investigated by the minimum inhibitory/bactericidal concentrations (MICs-MBCs), time-kill curves, and antibiofilm and antiadhesion assays. Bacterial interactions with the empty and GEN-THQ-loaded liposomes were evaluated using TEM.

The Lipo-GEN-THQ were spherical, monodispersed, and negatively charged. The Lipo-GEN-THQ were relatively stable and released GEN sustainably over 24 h. The liposomes exhibited significantly higher antibacterial activity than free GEN, as evidenced by the four-fold lower MIC and biofilm eradication in resistant E. coli strain (EC-219). TEM images display how the empty liposomes fused closely to the tested bacteria and how the loaded liposomes caused ultrastructure damage and intracellular component release. An antiadhesion assay showed that the Lipo-GEN-THQ and free GEN (0.125 mg/L) similarly inhibited Escherichia coli (EC-157) adhesion to the A549 cells (68% vs. 64%).

The Lipo-THQ-GEN enhanced GEN by combining it with THQ within the liposomes, reducing the effective dose. The reduction in the GEN dose after adding THQ may indirectly reduce the toxicity and aid in developing an enhanced and safer form of GEN.