Bactericidal and antibiotic-modulation activities of methanol crude extracts of Ligustrum lucidum and Lobelia inflata against MRSA phenotypes: Molecular docking studies of some isolated compounds from both plants against DNA gyrase A

Abstract

The present study evaluated antibacterial, plasmid conjugal transfer inhibition, growth kinetics and bacterial resistance modifying activities of methanol crude extracts from the fruits of Ligustrum lucidum (LLFE) and the leaves of Lobelia inflata (LILE) against a panel of methicillin-resistant Staphylococcus aureus (MRSA) expressing active efflux pumps. The results showed that both extracts had weak antibacterial activity against the MRSA strains to have MIC > 512 mg/L. The combination of extracts with standard antibiotics was synergistic (2–64 fold potentiation) and bactericidal (≤ 3log10 CFU/mL) on more than 70% of the bacteria. LLFE displayed a toxic effect on HepG2 cells having IC50 27.61 mg/L while LILE demonstrated moderate toxicity (IC50 125.06 mg/L). LILE extract exhibited a weak inhibition of transfer conjugation mediated by PKM 101 (30%) and promising inhibition against TP114 (74%), while LLFE enhanced conjugal transfer to both plasmids. The chromatogram peaks showed that both extracts contain rutin and gallic acid with a retention time corresponding to the standards at 330 nm. Molecular docking of lobelanidine showed that it was the safest and most potent inhibitor of DNA-gyrase A of Staphylococcus aureus when compared with the standard norfloxacin. Our findings suggest that Ligustrum lucidum and Lobelia inflata are potential pharmacological agents in the future design of combination anti-infective therapies against multidrug-resistant strains.