Rutin is a widely known plant secondary metabolite that exhibits multiple physiological functions. The present study focused on screening for synergistic antibacterial combinations containing rutin, and further explored the mechanisms behind this synergy. In vitro antibacterial test results of rutin showed that the ranges of minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) are 0.125–1 and 0.125–2 mg/mL, respectively. However, rutin and amikacin have a significant synergistic effect, with a fractional inhibitory concentration index (FICI) range of 0.1875–0.5. The time bactericidal curve proved that the combination of rutin and amikacin inhibited bacterial growth within 8 h. Scanning electron microscopy (SEM) revealed that a low-dose combination treatment could disrupt the cell membrane of Escherichia coli (E. coli). A comprehensive analysis using alkaline phosphatase (AKP), K⁺, and a protein leakage assay revealed that co-treatment destroyed the cell membrane of E. coli, resulting in the significant leakage of AKP, intracellular K⁺, and proteins. Moreover, confocal laser scanning microscopy (CLSM) and red–green cell ratio analysis indicated severe damage to the E. coli cell membrane following the co-treatment of rutin and amikacin. This study indicates the remarkable potential of strategically selecting antibacterial agents with maximum synergistic effect, which could significantly control antibiotic resistance.

Chlortetracycline hydrochloride (CTC) is a broad-spectrum tetracycline antibiotic used to prevent or resist different bacterial infections. However, due to its poor aqueous stability and physicochemical instability, its clinical development is limited. To improve such properties, CTC complexation with β-cyclodextrin (β-CD) and 2-hydroxypropanol-β-cyclodextrin (HP-β-CD) was performed using different preparation techniques (Freeze drying and ball milling). Inclusion complexes were comprehensively characterized using different analytical techniques and showed different properties distinct to pure CTC. In the presence of both CDs, CTC solubility was significantly improved. After ratio optimization, the optimal molar ratio after freeze-drying was determined to be 1:5. Compared to pure CTC powder (4 mg/mL), the solubility of CTC/HP-β-CD improved approximately 9 times (36 mg/mL), and a new CTC injection was successfully prepared. The antibacterial activity (in vivo and in vitro) of the CTC/HP-β-CD injection was then examined in natural infection chickens. Pathological tissue images showed that a 20 mg/kg CTC/HP-β-CD dose increased antibacterial activity and therapeutic effects. Additionally, we determined five clinical strains and statistically verified that CTC/HP-β-CD exhibits stronger antibacterial activity compared to CTC and other tetracycline drugs, with the most significant effect observed against Pseudomonas aeruginosa (MIC value of 2 μg/mL). Thus, these findings suggest that CTC/HP-β-CD inclusion complexes could be promising for pharmaceutical development, warranting further clinical evaluation, as solubility was significantly increased, and enhanced antibacterial activity was recorded in vivo and in vitro.

Chlortetracycline hydrochloride (CTC) is a broad-spectrum tetracycline antibiotic with a wide range of antibacterial activities. Due to low solubility, poor stability, and low bioavailability, clinical preparation development is limited. We sought to improve these solubility and dissolution rates by preparing solid dispersions. A hydrophilic polymer was selected as the carrier, and a solid dispersion was prepared using a medium grinding method, with samples characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), and particle size distribution (PSD). To maximize CTC solubility and stability, different polymer types and optimal drug-to-polymer ratios were screened. The solubility of optimized povidone K30 (PVPK30) (1/0.75, w/w)-, hydroxypropyl-β-cyclodextrin (HP-β-CD) (1/2, w/w)-, and gelatin (1/1, w/w)-based solid dispersions was 6.25-, 7.7-, and 3.75-fold higher than that of pure CTC powder, respectively. Additionally, in vitro dissolution studies showed that the gelatin-based solid dispersion had a higher initial dissolution rate. SEM and PS analyses confirmed that this dispersion had smaller and more uniform particles than PVPK30 and HP-β-CD dispersions. Therefore, successful solid polymer dispersion preparations improved the CTC solubility, dissolution rates, and stability, which may have potential as drug delivery systems.