Antibacterial and antibiotic-potentiation activities of methanol extracts from Blighia sapida K. D. Koenig (Sapindaceae) against Gram-negative multidrug-resistant bacteria overexpressing efflux pumps

Abstract

Background: The emergence and spread of multidrug-resistant (MDR) Gram-negative bacteria, particularly those overexpressing efflux pumps, make treatment difficult using conventional antibiotics. This study aims to assess the antibacterial activity of methanol extracts (botanicals) from the leaves (BSL) and bark (BSB) of Blighia sapida against a panel of MDR bacteria that overexpress efflux pumps.

Methods: Phytochemical screening of botanicals was carried out using standard qualitative assays. The antibacterial activity and the association of the botanicals with an efflux pump inhibitor (EPI), phenylalanine-arginine β-naphthylamide (PAβN), and antibiotics were evaluated using broth microdilution methods meanwhile the mode of action of BSL was investigated on proton pumps H+/ATPases assays.

Results: The secondary metabolites such as phenols, anthocyanins, saponins, alkaloids, and flavonoids were found in BSL and BSB. BSL and BSB showed activity against 93.33% and 60% of the isolates/strains, with minimum inhibitory concentrations (MICs) ranging from 16-1024 µg/mL. The addition of EPI increased the antibacterial activity of the botanicals against all tested bacteria. The botanicals also boosted the effectiveness of antibiotics at half MIC and quarter MIC, enhancing the activity of at least 57.14% of tetracycline (TET), ciprofloxacin (CIP), and imipenem (IMI) against the bacteria. When evaluated for its effects on the H+/ATPases proton pumps of Providencia stuartii ATCC29916, BSL showed potential in inhibiting the activity of this enzyme.

Conclusion: These results suggest that Blighia sapida contains secondary metabolites that can act alone or in combination with antibiotics to treat bacterial infections caused by MDR Gram-negative bacteria that overexpress efflux pumps.