Phytochemical characterization,antioxidant activity,and in vitro investigation of antimicrobial potential of Dittrichia viscosa L. leaf extracts against nosocomial infections

Dittrichia viscosa L., is a perennial plant belonging to the Asteraceae family, and this study was performed to investigate the chemical composition of its extract, using gas chromatography–mass spectrometry (GC–MS). Total phenol (TPC), flavonoid (TFC), and tannins contents (TTC), were quantified using colorimetric methods in two extracts (EtOH and ACE). The antioxidant activity was evaluated using DPPH scavenging, phosphomolebdenum test (TAC) and ferric reducing power assay (FRAP). The antimicrobial activity was determined against six nosocomial pathogens: Bacillus subtilis, Staphylococcus aureus, Salmonella enterica, Escherichia coli, Candida albicans, Aspergillus niger, using disc diffusion method and microdilution assay. The ACE and EtOH extracts had similar TPC: 151.18 ± 1.57 and 127.09 ± 15,81 mg GAE/ g DW. TFC & TTC recorded were also closely matched. The chemical composition revealed the presence of 18 phytochemical compounds with a total of 99.91%, where trimethylsilyl-meso-inositol (20.54%) was the major compound, followed by 5(4H)-Thebenidinone (16.80%). Both extracts showed high radical scavenging activity with an IC₅₀ equal to 12.54 ± 0.2 μg/mL for EtOH, and 7.84 ± 0.1 μg/mL for ACE in DPPH test. In the FRAP test, we recorded an EC₅₀ of 6.37 ± 0,012 mg/mL for EtOH, and 6 ± 0.022 mg/mL for ACE. The ACE presented higher antioxidant capacity (253.52 ± 2.98 mg AAE/g) compared to EtOH (189.14 ± 4,86 mg AAE/g) in the TAC assay. The higher inhibition zone was observed on B. subtilus (13 ± 0.1 mm) for EtOH, and the ACE was more effective on S. enterica (13.3 ± 0.08 mm). All the microbial strains were sensitive for both extracts, with MICs ranging from 0.93 mg/mL to 15 mg/mL.