Phytochemical and antibacterial properties of calyces Hibiscus sabdariffa L.: an in vitro and in silico multitarget-mediated antibacterial study
Authors: Ghaly Hend Khairy Fekry , Younis Fatema Aly Al-Yamany , Soliman Azza Mahmoud , El-Sabbagh Sabha Mahmoud 
Published: February 2025

Abstract

Background
Multidrug-resistant (MDR) bacteria pose a significant threat to human health worldwide by increasing the harmful impact of traditional synthetic antibiotics. Traditional medicinal plants have bioactive metabolites that can significantly modulate the growth rate, cell survival, and pathogenicity of antibiotic-resistant bacteria. Hibiscus sabdariffa L., known as Roselle or Karkade, belongs to the Malvaceae family. It is well-known for its edible aromatic red/purple calyces and is extensively utilized in the food industry and pharmacological applications. H. sabdariffa calyx bioactive phytocompounds have potent therapeutic activities such as antimicrobial, antidiabetic, antiobesity, antioxidant, anti-inflammatory, and anticancer properties.

Methods
This study utilized gas chromatography-mass spectrometry (GC-MS) analysis to determine the volatile aromatic compounds that found in the hydroethanolic extract of Hibiscus sabdariffa calyces. The purpose was to verify the antibacterial properties of Roselle calyces against selective MDR clinical bacterial isolates, including A. baumanii, E. coli, K. pneumoniae, and P. aeruginosa.

Results
The GC-MS spectrum profile revealed the presence of twenty-seven volatile organic components, including organic fatty acid derivatives, ester compounds, sugar derivatives, and terpene components. The major GC-MS fractionations and the main active chemical compositions of the hydroethanolic extract of H. sabdariffa flowers were (E)-10-Octadecenoic acid methyl ester (59.23%), 8,11-Octadecadienoic acid, methyl ester (11.51%), Butanedioic acid, 3-hydroxy-2,2-dimethyl-, diethyl ester (6.22%), Diethyl succinate/Butanedioic acid, diethyl ester (2.35%), and Heptadecanoic acid, 16-methyl-, methyl ester/Methyl isostearate (2.31%). The hydroethanolic extract of H. sabdariffa dried calyces demonstrated potent antibacterial properties (zones diameter of inhibition growth, MIC, MBC, and MBC/MIC) against selective MDR clinical bacterial isolates, such as A. baumanii, E. coli, K. pneumoniae, and P. aeruginosa, as determined by the phytochemical screening (TAC, TFC, and TPC) and antioxidant activity (DPPH). The surface morphological characteristics of the treated A. baumanii, E. coli, K. pneumoniae, and P. aeruginosa clinical isolates have been affected in comparison to the untreated forms by the hydroethanolic extract of H. sabdariffa calyces, as determined by scanning electron microscopy (SEM). In silico predictive investigation revealed that the volatile aromatic components of the hydroethanolic extract of Roselle calyces exhibited significant scoring functions, binding affinities, and non-covalent intermolecular interactions with the MenB lyase and DNA gyrase targets of E. coli. These interactions significantly enhanced the activities of the volatile aromatic components against the bacterial pathogenicity, cell survival, growth, and differentiation of selective MDR clinical bacterial isolates.

Conclusions
According to the in vitro and in silico findings, the hydroethanolic extract of H. sabdariffa calyces has shown potentials as an effective antioxidant and antibacterial treatment. It contains volatile aromatic compounds that can modulate selective MDR Gram-negative clinical bacterial isolates.