Targeting Multidrug-Resistant Uropathogenic Escherichia coli from a Tertiary Care Hospital: Promising Antibacterial and Antioxidant Activities of the Brown Seaweed Sargassum vulgare Extract

Abstract

Antimicrobial resistance (AMR) among uropathogenic Escherichia coli (UPEC) has become a major global health concern, highlighting the urgent need for alternative therapeutic agents. Marine macroalgae are considered promising natural sources of bioactive compounds with antimicrobial and antioxidant properties. This study investigated the antibacterial, antioxidant, and cytotoxic activities of Sargassum vulgare extract against multidrug-resistant (MDR) UPEC isolated from urinary tract infection (UTI) patients. Fifty urine samples collected from patients at Sayed Galal Hospital were microbiologically analyzed, and bacterial isolates were identified using conventional methods and confirmed by 16S rRNA gene sequencing. Antibiotic susceptibility testing was performed using the Kirby-Bauer disk diffusion method. An ethanol extract of S. vulgare, collected from the Red Sea and taxonomically authenticated, was evaluated for antibacterial activity using agar well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays. Phytochemical constituents were identified using Gas Chromatography-Mass Spectrometry (GC-MS), while antioxidant activity was determined by DPPH, FRAP, and total antioxidant capacity (TAC) assays. Cytotoxicity was assessed against Vero cells using the MTT assay. Among the 50 urine samples, 40 (80%) showed significant bacterial growth. Gram-positive bacteria represented 60% of the isolates, whereas Gram-negative bacteria accounted for 40%. Only one isolate exhibited multidrug resistance. The S. vulgare extract demonstrated significant antibacterial activity against the selected MDR UPEC isolate, with an inhibition zone of 18±0.4 mm, MIC of 128±0.2 µg/mL, and MBC of 256±0.3 µg/mL. GC-MS analysis revealed major bioactive compounds, including 9-Octadecenoic acid (Z)-, methyl ester (44.6%), 9-Octadecenoic acid (Z)- (25.97%), and Tetradecanoic acid, 12-methyl, methyl ester (16.28%). The extract also exhibited strong antioxidant activity and low cytotoxicity against Vero cells (IC50 = 858.38 ± 62.33 µg/mL), yielding a favorable selectivity index (SI = IC50/MIC) of 6.71. These preliminary findings, although based on a single MDR clinical isolate, suggest that S. vulgare possesses potential antibacterial and antioxidant potential and warrants further investigation as a natural source of anti-infective agents. However, extensive validation against a broader panel of clinical isolates is essential before any therapeutic applications can be considered.