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The global spread of multidrug-resistant strains has prompted the scientific community to explore novel sources of chemicals with antimicrobial activity. The aim of the study was to examine the antimicrobial activity in vitro of 28 extracts against carbapenem-producing Klebsiella pneumoniae, individually and in combination with antibiotics and in vivo toxicological assessment of the most active product. The multi-resistant K. pneumoniae strain was submitted for phenotypic and molecular characterization. The antibacterial activity of 28 plant extracts was evaluated alone and in combination with antibiotics against this strain through the agar disk diffusion. Of these, 16 extracts showed synergism against carbapenem-producing K. pneumoniae, being that B. crassifolia extract exhibited synergism with three antibiotics. Based on this assessment, B. crassifolia-extract-induced toxicity on Swiss male mice was evaluated by administering this extract and subsequently determining apoptosis and splenic phagocytosis using the comet and micronucleus assays. The results of this study showed that B. crassifolia extract had synergistic activity promising and groups treated with B. crassifolia exhibited no genotoxic or mutagenic activity, indicating that B. crassifolia extract exerted beneficial effects and appeared safe to use at the studied concentrations. [ABSTRACT FROM AUTHOR]

Multidrug-resistant Acinetobacter baumannii has emerged as a problematic hospital-acquired pathogen. It is vital to search for new sources of antibiotics. Natural plant essential oils have several biological properties, including antimicrobial activity and may be valuable for new drug development. Chemical composition of the essential oil of Nectandra megapotamica flowers was assessed by Gas Chromatography/Flame Ionization Detector and Gas Chromatography/Mass Spectrometry analysis. Antibacterial activity against OXA-23-producing A. baumannii and synergism with antibiotics were performed by broth microdilution, time kill, and checkerboard methods. The essential oil of Nectandra megapotamica flowers showed a predominance of oxygenated sesquiterpenes and caryophyllene oxide was the main component. Survival curves showed a linear decrease in viable OXA-23-producing A. baumannii cell counts over time for the association between the essential oil of Nectandra megapotamica flowers and imipenem. Checkerboard assay with imipenem presented Fractional Inhibitory Concentration Index of 0.156, suggesting synergism. The synergistic effect of essential oil of Nectandra megapotamica flowers with imipenem could be a potential approach to combat multiresistant OXA-23-producing A. baumannii strains, and could be used as a drug delivery system, as an excipient for imipenem, reducing its dosage. [ABSTRACT FROM AUTHOR]