| Summary: | This study reported the phytochemical composition of two hydroethanolic extracts of <i>Acacia senegal</i> and <i>Acacia seyal</i> trees from Burkina Faso and their activities, alone or in combination with selected antibiotics, against multidrug resistant bacteria. High performance thin layer chromatography (HPTLC) method was used for phytochemical screening. Total phenolic and total flavonoid ant tannins in leaves extracts contents were assessed by spectrophotometric method. The minimal inhibitory concentrations (MICs) of plant extracts and antibiotics were determined using the microdilution method and <i>p</i>-iodonitrotetrazolium chloride. Combinations of extracts and antibiotics were studied using checkerboard assays. Screening revealed the presence of phenolic compounds, flavonoids, and tannins in the hydroethanolic extract (HE) of the leaves. The HE of <i>A. seyal</i> showed the highest total phenolic (571.30 ± 6.97 mg GAE/g), total flavonoids (140.41 ± 4.01 mg RTE/g), and tannins (24.72 ± 0.14%, condensed; 35.77 ± 0.19%, hydrolysable tannins). However, the HE of <i>A. senegal</i> showed the lowest total phenolic (69.84 ± 3.54 mg GAE/g), total flavonoids (27.32 ± 0.57 mg RTE/g), and tannins (14.60 ± 0.01%, condensed; 3.09 ± 0.02%, hydrolysable). The MICs for HE and antibiotics were in the range of 2–512 and 0.008–1024 mg/L, respectively. All tested HE presented an MIC greater than 512 mg/L except HE of <i>A. senegal</i>. The lowest MIC value (128 mg/L) was obtained with HE of <i>A. senegal</i> against <i>Klebsiella aerogenes</i> EA298 and <i>Escherichia coli</i> AG100A. Interesting restoring effects on chloramphenicol and florphenicol activity were detected with alcoholic extracts of <i>A. senegal</i> against resistant <i>E. coli</i> and <i>K. aerogenes</i> strains that overproduce AcrAB or FloR pumps. The adjuvant effect of HE of <i>A. senegal</i> suggests that the crude extract of leaves could be a potential source of molecules for improving the susceptibility of bacteria to phenicols antibiotics.
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