Plant-derived secondary metabolites as the main source of efflux pump inhibitors and methods for identification

The upsurge of multiple drug resistance(MDR)bacteria substantially diminishes the effectiveness of antibiotic arsenal and therefore intensifies the rate of therapeutic failure.The major factor in MDR is efflux pump-mediated resistance.A unique pump can make bacteria withstand a wide range of structurally diverse compounds.Therefore,their inhibition is a promising route to eliminate resistance phenomenon in bacteria.Phytochemicals are excellent alternatives as resistance-modifying agents.They can directly kill bacteria or interact with the crucial events of pathogenicity,thereby decreasing the ability of bacteria to develop resistance.Numerous botanicals display noteworthy efflux pumps inhibitory activities.Edible plants are of growing interest.Likewise,some plant families would be excellent sources of efflux pump inhibitors(EPIs)including Apocynaceae,Berberidaceae,Convolvulaceae,Cucurbitaceae,Fabaceae,Lamiaceae,and Zingiberaceae.Easily applicable methods for screening plant-derived EPIs include checkerboard synergy test,berberine uptake assay and ethidium bromide test.In silico highthroughput virtual detection can be evaluated as a criterion of excluding compounds with efflux substrate-like characteristics,thereby improving the selection process and extending the identification of EPIs.To ascertain the efflux activity inhibition,real-time PCR and quantitative mass spectrometry can be applied.This review emphasizes on efflux pumps and their roles in transmitting bacterial resistance and an update plant-derived EPIs and strategies for identification.

Whole Genome Analysis Reveals New Insights into Macrolide Resistance in Mycoplasma pneumoniae

Objective Mutations in 23 S rRNA gene are known to be associated with macrolide resistance in Mycoplasma pneumoniae（M. pneumoniae）. However, these mutations alone do not fully explain the high resistance rates in Asia. The aim of this study was to investigate other possible mutations involved in macrolide resistance in M. pneumoniae. Methods The whole genomes of 10 clinical isolates of M. pneumoniae with macrolide resistance were sequenced by Illumina Hi Seq2000 platform. The role of the macrolide-specific efflux transporter was assessed by efflux-pump inhibition assays with reserpine and carbonyl cyanide m-chlorophenyl-hydrazone（CCCP）. Results A total of 56 single nucleotide polymorphisms（SNPs） were identified in 10 clinical isolates in comparison to the reference strains M129 and FH. Strikingly, 4 of 30 SNPs causing non-synonymous mutations were clustered in macrolide-specific efflux system gene mac B encoding macrolide-specific efflux pump protein of the ATP-binding cassette transporter family. In assays of the minimal inhibitory concentrations（MIC） of macrolide antibiotics in the presence of the efflux pump inhibitors caused a significant decrease of MICs, even under detectable levels in some strains. Conclusion Our study suggests that macrolide efflux pump may contribute to macrolide resistance in M. pneumoniae in addition to the common point mutations in 23 S r RNA gene.

Reversal of Tetracycline Resistance by Cepharanthine,Cinchonidine,Ellagic Acid and Propyl Gallate in a Multi-drug Resistant Escherichia coli

Bacterial resistance to antibiotics is an increasing threat to global healthcare systems.We therefore sought compounds with potential to reverse antibiotic resistance in a clinically relevant multi-drug resistant isolate of Escherichia coli(NCTC 13400).200 natural compounds with a history of either safe oral use in man,or as a component of a traditional herb or medicine,were screened.Four compounds;ellagic acid,propyl gallate,cinchonidine and cepharanthine,lowered the minimum inhibi-tory concentrations(MICs)of tetracycline,chloramphenicol and tobramycin by up to fourfold,and when combined up to eightfold.These compounds had no impact on the MICs of ampicillin,erythromycin or trimethoprim.Mechanistic studies revealed that while cepharanthine potently suppressed efflux of the marker Nile red from bacterial cells,the other hit com-pounds slowed cellular accumulation of this marker,and/or slowed bacterial growth in the absence of antibiotic.Although cepharanthine showed some toxicity in a cultured HEK-293 mammalian cell-line model,the other hit compounds exhibited no toxicity at concentrations where they are active against E.coli NCTC 13400.The results suggest that phytochemicals with capacity to reverse antibiotic resistance may be more common in traditional medicines than previously appreciated,and may offer useful scaffolds for the development of antibiotic-sensitising drugs.