Flavonoid-Mediated Biofilm Inhibition and Toxicological Evaluation of Atriplex laciniata Against Multidrug-Resistant MRSA

Bandar Almutairy^*

• College of Pharmacy, Shaqra University, Al-Dawadmi, Saudi Arabia

Multidrug-resistant (MDR) superbugs threaten the efficacy of antibiotics, so new drug formulations from synthetic or natural sources are needed to combat antimicrobial resistance (AMR). Traditional herbs are considered an alternative approach to treating AMR and MDR infections. The current study evaluated the efficacy and safety of Atriplex laciniata extracts, AL-Aq-Ext (aqueous extract) and AL-Flv-Ext (flavonoid-rich extract), against MDR MRSA strains. Their efficacy was tested against MRSA by evaluating bacterial viability and biofilm inhibition. It was confirmed through MTT assays, OD 600 nm measurement, confocal laser scanning microscopy (CLSM) for morphological observations, and the amyloid staining Congo-red phenotypic method. Safety was evaluated through comprehensive toxicological assessments, including acute toxicity, tissue biocompatibility, vital organ toxicity, and relative hemolysis. The major results indicated MRSA cell viability at minimum inhibitory concentrations (MICs) of 512 µg/mL for AL-Aq-Ext and 256 µg/mL for AL-Flv-Ext. At these MIC concentrations, the extracts also exhibited bactericidal effects, with comparable zones of inhibition (ZOIs): AL-Aq-Ext (22 mm) and AL-Flv-Ext (20 mm), contrasted with vancomycin (25 mm). Both extracts showed more than 90% biofilm inhibition, confirmed through OD 600 nm measurements, morphological detection by decline in fluorescence intensities via CLSM, and phenotypically by the Congo-red amyloid staining assay. Time-kill kinetics assays indicated prolonged bactericidal effects lasting 73 hours against MRSA. Regarding safety, acute toxicity studies were conducted by administering MIC doses of AL-Aq-Ext and AL-Flv-Ext orally to mice over 10 days, revealing 100% survival rates and no immediate adverse effects. Histopathological analysis of vital organs (liver and kidney) showed no tissue damage, confirming the absence of acute organ toxicity, while hemolysis assays demonstrated no red blood cell lysis at any tested concentration, indicating excellent blood compatibility. These findings demonstrate that A. laciniata extracts (AL-Aq-Ext and AL-Flv-Ext) are rich in flavonoids, safe, biocompatible, and suitable for further pharmacological development, with promising potential for preclinical and clinical trials. However, the study is limited to acute toxicity and short-term exposure; future research should focus on identifying specific bioactive compounds, evaluating long-term toxicity, studying pharmacokinetics, assessing efficacy in disease models, and investigating potential immunogenicity and drug interactions to fully establish their therapeutic potential.