Antibacterial potential and modes of action of botanicals from Momordica foetida (Cucurbitaceae) against multidrug-resistant bacteria expressing active efflux pumps

Abstract

Background: Momordica foetida (cucurbitaceae) known as a bitter cucumber in Cameroon is used as a medicinal plant. This plant is widely used in the treatment of microbial infections, diabetes, hypertension, stomach, and intestinal irritation. The leaves are also used to treat malaria, earache, and toothache. This study aimed at investigating the antibacterial activity of the methanol extract of M. foetida seeds against multidrug-resistant bacteria expressing active efflux pumps and to characterize the mode of action of this extract.

Methods: The antibacterial activity of the crude extract of M. foetida in the presence and absence of an efflux pump inhibitor, phenylalanine-arginine β-naphthylamide (PAβN), was evaluated by the serial micro-dilution method. The determination of the effect of this sample on bacterial H⁺-ATPase proton pumps was performed by a standard method using a pH meter and the study of the effect of the same sample on cell growth kinetics, bacterial membrane, and biofilms was performed by a spectrophotometric method.

Results: The phytochemical composition of the crude extract of M. foetida, evaluated using standard qualitative methods, showed a rather selective distribution of secondary metabolites (presence of polyphenols, flavonoids, alkaloids, triterpenes, sterols, and saponins). The crude extract of this plant virtually inhibited the growth of 90.90% (20/22) of the bacteria studied with minimal inhibitory concentrations (MIC) ranging from 64 to 1024 µg/mL. The lowest MIC of 64 µg/mL was observed against Escherichia coli (AG102, MC4100, W3110), Klebsiella pneumoniae (KP55 and ATCC 11296), Providencia stuartii (NEA16, ATCC 29916 and PS2636), Pseudomonas aeruginosa (PA124) and Staphylococcus aureus (MRSA9) strains. In the presence of PAβN, the activity of the extract was increased against all strains and isolates used. The crude extract caused a prolongation of the lag phase and a general decrease in the growth of Escherichia coli AG102 bacteria due to the blocking of the H⁺-ATPase proton pumps of this bacterium, resulting in a decrease in the acidity of the medium. This sample destroyed the bacterial membrane and showed significant activity on the biofilms of this strain tested.

Conclusion: The results obtained in the present work provide important and significant data that could allow the probable use of Momordica foetida in the control of bacterial infections.