Phylogenetic spectrum and analysis of antibacterial activities of leaf extracts from plants of the genus Rhododendron

Abstract

BackgroundPlants are traditionally used for medicinal treatment of numerous human disorders including infectious diseases caused by microorganisms. Due to the increasing resistance of many pathogens to commonly used antimicrobial agents, there is an urgent need for novel antimicrobial compounds. Plants of the genus Rhododendron belong to the woody representatives of the family Ericaceae, which are typically used in a range of ethno-medical applications. There are more than one thousand Rhododendron species worldwide. The Rhododendron-Park Bremen grows plants representing approximately 600 of the known Rhododendron species, and thus enables research involving almost two thirds of all known Rhododendron species.MethodsTwenty-six bacterial species representing different taxonomic clades have been used to study the antimicrobial potential of Rhododendron leaf extracts. Agar diffusion assay were conducted using 80% methanol crude extracts derived from 120 Rhododendron species. Data were analyzed using principal component analysis and the plant-borne antibacterial activities grouped according the first and second principal components.ResultsThe leaf extracts of 17 Rhododendron species exhibited significant growth-inhibiting activities against Gram-positive bacteria. In contrast, only very few of the leaf extracts affected the growth of Gram-negative bacteria. All leaf extracts with antimicrobial bioactivity were extracted from representatives of the subgenus Rhododendron, with 15 from the sub-section Rhododendron and two belonging to the section Pogonanthum. The use of bacterial multidrug efflux pump mutants revealed remarkable differences in the susceptibility towards Rhododendron leaf extract treatment.ConclusionsFor the first time, our comprehensive study demonstrated that compounds with antimicrobial activities accumulate in the leaves of certain Rhododendron species, which mainly belong to a particular subgenus. The results suggested that common genetic traits are responsible for the production of bioactive secondary metabolite(s) which act primarily on Gram-positive organisms, and which may affect Gram-negative bacteria in dependence of the activity of multidrug efflux pumps in their cell envelope.Electronic supplementary materialThe online version of this article (doi:10.1186/s12906-015-0596-5) contains supplementary material, which is available to authorized users.

Incongruent phylogenies and its implications for the study of diversification, taxonomy and genome size evolution of Rhododendron (Ericaceae)

“…Oswald and Nuismer (2007) explored the possibility that new polyploids are initially more resistant to pathogens than their diploid progenitors by using mathematical models and confirmed that polyploids are significantly more resistant. Rhododendron may prove to be a living example for the evolution of novel chemicals in polyploids since four of the ten species shown to exhibit the highest antibacterial effects against Gram-positive bacteria by Rezk et al (2015) are shown here to be polyploid (R. ambiguum, R. cinnabarinum, R. concinnum and R. rubiginosum). It remains to be shown that the high antimicrobial activity is due to the origin of novel gene combinations in polyploids.…”

Antibacterial Activities of Ethanolic Extract Obtained from Rhododendron Myrtifolium Schott & Kotschy Leaves Against Clinically Isolated Bacterial Strains

“…A higher antibacterial effect of Rhododendron species against Gram-positive and higher effect for R. cinnabarinum was demonstrated in the antibacterial screening by Rezk et al (2015a ., Tkachenko, H., Prokopiv, A., Nachychko, V., Sosnovsky, Y., Góralczyk, A., Osadowski, Z. Agr.bio.div. Impr.…”

“…Only one Gram-negative species, Sinorhizobium meliloti, belonging to the order of α-proteobacteria exhibited susceptibility to most of the bioactive Rhododendron extracts and was therefore similar in its susceptibility to the majority of Gram-positive bacteria. The results of Rezk et al (2015a) suggested that common genetic traits are responsible for the production of bioactive secondary metabolite(s) which act primarily on Gram-positive organisms, and which may affect Gramnegative bacteria independence of the activity of multidrug efflux pumps in their cell envelope.…”

Isolation, identification, and biological control in vitro of tail rot pathogen strain from Hippocampus kuda

“…The susceptibilities of the pathogen to various bioactive agents were performed by following the agar diffusion-inhibition method with some modifications [36]. Strain HL11 was diluted to a final concentration of 10 8 cfu/mL with sterile distilled water.…”