Antioxidant, Antibacterial, and Antibiofilm Activities of Selected Medicinal Plant Extracts with In Vivo Protection against E. coli Infection

The present study assesses the yield, phytochemical composition, antioxidant properties, antibacterial activity, antibiofilm efficacy, and in vivo impacts of four plant extracts: Cassia fistula (CFLex), Callistemon viminalis (CVLex), Delonix regia (DRLex), and Simarouba glauca (SGLex). Among these, SGLex exhibited the highest extractive yield (18.07%), and was characterized by a high phenolic content (82.48 mg GAE/g) and flavonoid content (47.54 mg QE/g), which correlates with its strong antioxidant activity. SGLex also demonstrated notable free radical scavenging abilities, with DPPH (85.69%) and ABTS (53.67%) inhibition. Antimicrobial assays showed that SGLex effectively inhibited E. coli growth (19.00 mm inhibition zone), while DRLex showed no antibacterial activity. Additionally, SGLex exhibited the most significant decrease in E. coli cell surface hydrophobicity (21.90%) and the most potent antibiofilm action (76.52%). In vivo, E. coli-infected Sprague Dawley rats experienced weight loss, reduced food and water intake, and increased fecal moisture content. These symptoms were notably improved following SGLex treatment (G6), which restored body weight and normalized fecal parameters while also significantly reducing viable E. coli counts (2.99 Log CFU/g), comparable to the uninfected control group. Overall, these findings highlight the significant bioactive properties of SGLex, including its antioxidants, antibacterial, and antibiofilm activities, along with its therapeutic potential in vivo effect against E. coli infection. The results support its promise as a natural medicinal agent for application in food preservation and medical uses.