Antibiogramic Efficacy of Cymbopogan citratus, Ocimum gratissimum, and Kalanchoe pinnata Methanolic and Aqueous Extracts on Colistin-Resistant Non-Clinical Isolates of Gram-negative Bacteria

Abstract

Antibiotic resistance is a significant global public health concern, with recent reports indicating that Gram-negative bacteria are developing resistance to colistin, a last-resort antibiotic.  This study aimed to assess the antibacterial effects of methanolic and aqueous leaf extracts from Ocimum gratissimum, Kalanchoe pinnata, and Cymbopogan citratus medicinal plants against colistin-resistant bacteria.  The extracts were obtained through maceration, followed by qualitative phytochemical analysis (including alkaloids, flavonoids, glycosides, saponins, sterols, phenolic compounds, and tannins) and quantitative evaluation of alkaloids, flavonoids, and tannins.  Furthermore, antibacterial properties were tested against twelve colistin-resistant Gram-negative bacterial strains using the disc diffusion method.  Qualitative analysis revealed the presence of flavonoids, proteins, carbohydrates, and tannins in all leaf extracts, while amino acids, fixed oil, and fats were absent.  The highest flavonoid content was found in the methanolic extract of C. citratus (153 ± 2.7µg/ml) and the lowest in the aqueous extract of K. pinnata (0.0 ± 0.0µg/ml).  Tannin levels were highest in the methanolic extract of O. gratissimum (282.4 ± 13.5µg/ml) and lowest in the aqueous extract of C. citratus (27.1 ± 5.7µg/ml).  Phenolic compound concentrations ranged from 136.9 ± 58.0µg/ml (methanolic extract of O. gratissimum) to 14.5 ± 2.9µg/ml (aqueous extract of K. pinnata).  The antibacterial activity of the methanolic extracts of O. gratissimum, K. pinnata, and C. citratus exhibited varied results, with all isolates resistant to all concentrations of the leaf extracts.  However, the aqueous extract of Ocimum gratissimum inhibited Providencia stuarti at 250mg, while Enterococcus dispar and Escherichia coli were sensitive to the aqueous leaf extracts of Ocimum gratissimum across all concentrations.  These findings indicate increasing resistance of Gram-negative bacteria to colistin and various concentrations of the methanolic and aqueous extracts of the three medicinal plants.