A moderately active crude methanol extract from the whole plant of Kalanchoe crenata (Andrews) Haw. (Crassulaceae) strongly potentiated the effect of antibiotics against multidrug-resistant Gram-negative bacteria

Abstract

Background: Resistant bacteria develop a high level of resistance to multiple drugs, limiting treatment options and increasing morbidity and mortality. This work was planned to evaluate the antibacterial potential of the methanol extract from the whole plant of Kalanchoe crenata (KCW) against multidrug-resistant (MDR) Gram-negative bacteria.

Methods: The minimal inhibitory concentrations (MIC) and the minimal bactericidal concentrations (MBC) of KCW alone, in the presence of an efflux pump inhibitor (EPI) phenylalanine-arginine β-naphthylamide (PAβN), or in the presence of antibiotics were assessed using the broth microdilution method combined with the rapid para-iodonitrotetrazolium chloride (INT) colorimetric technique.

Results: KCW displayed weak antibacterial activities with MIC values ranging from 128 to 1024 μg/mL against 10 of the 15 tested bacterial strains. Moderate antibacterial activities with MIC values ranging from 128-625 μg/mL were recorded against some strains belonging to Klebsiella pneumoniae, Escherichia coli, and Providencia stuartii. PAβN does not significantly enhance the activity KCW. At MIC/2, KCW potentiated the activity of doxycycline (DOX), levofloxacin (LEV), imipenem (IMI), ciprofloxacin (CIP), ceftriaxone (CRO), and tetracycline (TET) against at least 80% of the MDR bacterial strains tested.

Conclusion: The present study demonstrated that KCW is a moderately active antibacterial agent, but a good efflux pump inhibitor that could potentiate the activity of antibiotics against MDR bacteria over-expressing active efflux pumps.