Antibacterial and Immunomodulatory Effects of Withania somnifera Ethanolic Root Extract Against Colistin-Resistant Acinetobacter baumannii in Leukopenic Mice

Acinetobacter baumannii, particularly colistin-resistant strains, represents a major therapeutic challenge because of multidrug resistance, biofilm formation, and limited treatment options. This study investigated the antibacterial, antibiofilm, immunomodulatory, and therapeutic potential of Withania somnifera ethanolic root extracts (WSEEs) against drug-sensitive (DS) and colistin-resistant (CR) A. baumannii. WSEE exhibited concentration-dependent antibacterial activity, with MIC/MBC values of 125/250 μg/mL against the DS isolate and 250/500 μg/mL against the CR isolate. Time–kill analysis demonstrated bactericidal activity at 250 μg/mL, and WSEE significantly reduced the biomass of preformed biofilms. In cyclophosphamide-induced leukopenic mice, oral administration of WSEE (100 and 200 mg/kg) restored leukocyte counts and significantly reduced pulmonary bacterial burden following infection with both isolates. The higher dose (200 mg/kg) achieved survival rates of 90% and 70% in mice infected with the DS and CR isolates, respectively, compared with 50% and 30% in the corresponding colistin-treated groups. WSEE also significantly decreased serum levels of the pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), indicating attenuation of infection-associated inflammation. Biochemical analyses further showed that WSEE did not produce detectable hepatotoxicity or nephrotoxicity under the experimental conditions. Collectively, these findings demonstrate that WSEE possesses antibacterial, antibiofilm, anti-inflammatory, and immunomodulatory activities and provides therapeutic benefit in experimental A. baumannii infection. These results support the potential of WSEE as a complementary therapeutic strategy against multidrug-resistant A. baumannii, while further mechanistic, pharmacokinetic, and translational studies are needed to validate its clinical potential.