Antibacterial synergism of Echeveria subrigida (B. L. Rob & Seaton) and commercial antibiotics against multidrug resistant Escherichia coli and Staphylococcus aureus

Abstract

IntroductionMultidrug-resistant (MDR) bacteria is a public health threat, which requires the development of new therapeutic options. The combined use of plant extracts with commercial antibiotics is an alternative against infections by MDR bacteria. Echeveria subrigida is a Crassulaceae plant with very good activity against some bacteria. This study aims to evaluate the synergistic effect of the methanol extract of Echeveria subrigida leaves (ME-ES) with commercial antibiotics against MDR isolates of Escherichia coli and Staphylococcus aureus. MethodsSix antibiotics, E. coli (4 MDR isolates and ATCC 25922) and S. aureus (2 MDR isolates and ATCC 29213) were used. ATCC strains were susceptible to the corresponding antibiotics and used as controls. The minimal inhibitory (MIC) and bactericidal (MBC) concentrations were evaluated by the microdilution broth assay, and the synergistic effect by the checkerboard and the time-kill curve methods. ResultsThe MDR of the bacterial isolates was corroborated, they were resistant to at least two families of antibiotics. The activity of ME-ES was good against one MDR E. coli isolate (MIC=250μg/mL) and the S. aureus strains (MIC=250–1000μg/mL), which was better than those registered for some commercial antibiotics. Synergism against S. aureus was found for the combinations ME-ES with carbenicillin and ME-ES with methicillin (FICI=0.28 to 0.5). ConclusionsME-ES was active against S. aureus and increased its activity when combined with betalactamic antibiotics. ME-ES can contribute to providing a best treatment for infectious diseases caused by MDR S. aureus.