# Phytochemical Composition and Antipseudomonal Activity of Allanblackia gabonensis (Clusiaceae) Extracts Alone and With Antibiotics Against Drug‐Resistant Clinical Isolates

## TL;DR

This study explores the antibacterial potential of Allanblackia gabonensis extracts against drug-resistant Pseudomonas aeruginosa, both alone and in combination with antibiotics.

## Contribution

The study identifies synergistic effects of A. gabonensis extracts with aminoglycoside antibiotics against multidrug-resistant Pseudomonas aeruginosa.

## Key findings

- Hexane leaf and bark extracts showed strong antibacterial activity with MIC ≤ 32 μg/mL against MDR P. aeruginosa.
- Sub-inhibitory concentrations of extracts enhanced antibiotic activity by up to 256-fold.
- Hexane and methanol bark extracts synergized with aminoglycosides (∑FIC ≤ 0.5).

## Abstract

The discovery of alternative therapies for illnesses due to multidrug‐resistant (MDR) bacteria is emerging as a global health crisis. This study aimed to assess the antibacterial efficacy of Allanblackia gabonensis extracts, both alone and in conjunction with antibiotics, against MDR Pseudomonas aeruginosa.

The extracts were subjected to phytochemical analysis using both qualitative and quantitative standard tests. The microdilution assay was used to evaluate the antibacterial properties and antibiotic resistance‐modifying potential of the extracts. The interaction effect between the antibiotics and extracts was determined by checkerboard assay. Catalase activity and lipid peroxidation were assessed by measuring the foam height and malondialdehyde concentration, respectively.

The extracts exhibited minimum inhibitory concentrations (MICs) ranging from 16 to 2048 μg/mL. The hexane extracts of the leaves (HLE) and bark (HBE) displayed the highest antibacterial activity, with MIC ≤ 32  μg/mL against at least two investigated isolates. Furthermore, HLE decreased catalase activity and increased lipid peroxidation in P. aeruginosa D130. The extracts at their sub‐inhibitory concentration (MIC/8) enhanced the activity of antibiotics, mainly aminoglycosides (amikacin, streptomycin, and gentamicin), by 2‐ to 256‐fold against selected MDR P. aeruginosa. Among these extracts, the hexane and methanol bark extracts exhibited synergy (∑FIC ≤ 0.5)) in combination with these antibiotics. All examined extracts contained alkaloids, phenols, and triterpenes. Moreover, dichloromethane/methanol and methanol leaf extracts presented the highest phenolic content.

Overall, the leaf and bark hexane extracts of A. gabonensis could serve as candidates for the discovery of new antibiotics, while its bark extracts might be used in conjunction with antibiotics to manage infections involving multidrug‐resistant P. aeruginosa.