Abstract
BackgroundTraditional medicinal plants have been used as an alternative medicine in many parts of the world, including Ethiopia. There are many documented scientific reports on antimicrobial activities of the same. To our knowledge, however, there is no report on the anti-Quorum Sensing (Quorum Quenching, QQ) potential of traditional Ethiopian medicinal plants. As many of the opportunistic pathogenic bacteria depend on Quorum Sensing (QS) systems to coordinate their virulence expression, interference with QS could be a novel approach to control bacterial infections. Thus, the aim of this study was to evaluate selected medicinal plants from Ethiopia for their antimicrobial activities against bacterial and fungal pathogens; and to assess the interference of these plant extracts with QS of bacteria.MethodsAntimicrobial activities of plant extracts (oil, resins and crude extracts) were evaluated following standard agar diffusion technique. The minimum inhibitory concentrations (MIC) of potent extracts were determined using 96 well micro-titer plates and optical densities were measured using an ELISA Microplate reader. Interference with Quorum Sensing activities of extracts was determined using the recently established E. coli based reporter strain AI1-QQ.1 and signaling molecule N-(ß-ketocaproyl)-L-homoserine lactone (3-oxo-C6-HSL).ResultsPetroleum ether extract of seed of Nigella sativa exhibited the highest activity against both the laboratory isolated Bacillus cereus [inhibition zone (IZ), 44 ± 0.31 mm] and B. cereus ATCC 10987 (IZ, 40 ± 2.33 mm). Similarly, oil extract from mature ripe fruit husk of Aframomum corrorima and mature unripe fruit of A. corrorima revealed promising activities against Candida albicans ATCC 90028 (IZ, 35 ± 1.52 mm) and Staphylococcus aureus DSM 346 (IZ, 25 ± 1.32 mm), respectively. Antimicrobial activities of oil extract from husk of A. corrorima and petroleum ether extract of seed of N. sativa were significantly higher than that of the control antibiotic [Gentamycin sulfate, (IZ, 25–30 mm)]. The lowest MIC value (12.5 mg/mL) was recorded for oil from husk of A. corrorima against Pseudomonas aeruginosa. Of the total eighteen extracts evaluated, two of the extracts [Methanol extract of root of Albiza schimperiana (ASRM) and petroleum ether extract of seed of Justica schimperiana (JSSP)] interfered with cell-cell communication most likely by interacting with the signaling molecules.ConclusionTraditional medicinal plants from Ethiopia are potential source of alternative medicine for the local community and scientific research in search for alternative drugs to halt challenges associated with the emerging antimicrobial resistance. Furthermore, the Quorum Quenching activities observed in two of the plant extracts calls for more comprehensive evaluation of medicinal plants for the control of many bacterial processes and phenotypic behaviors such as pathogenicity, swarming, and biofilm formation. Being the first assessment of its kind on the potential application of Ethiopian traditional medicinal plants for interference in microbial cell-cell communication (anti-Quorum Sensing activities), the detailed chemistry of the active compounds and possible mechanism(s) of actions of the bio-molecules responsible for the observed interference were not addressed in the current study. Thus, further evaluation for the nature of those active compounds (bio-molecules) and detailed mechanism(s) of their interaction with microbial processes are recommended.
Highlights
Traditional medicinal plants have been used as an alternative medicine in many parts of the world, including Ethiopia
Being the first assessment of its kind on the potential application of Ethiopian traditional medicinal plants for interference in microbial cell-cell communication, the detailed chemistry of the active compounds and possible mechanism(s) of actions of the bio-molecules responsible for the observed interference were not addressed in the current study
Screening for antimicrobial activity The degree of inhibition, as determined by values of diameter of inhibition zone (IZ) of respective extracts, varied among the extracts with the highest inhibition being recorded for petroleum ether extract of seed of Nigella sativa against Bacillus cereus (IZ, 44 ± 0.31 mm), B. cereus American type culture collection (ATCC) 10987 (IZ, 40 ± 2.33 mm), oil from mature ripe fruit husk of Aframomum corrorima against Candida albicans ATCC 90028 (IZ, 35 ± 1.52 mm) and mature unripe fruit oil of A. corrorima against S. aureus (IZ, 25 ± 1.32 mm) (Table 2)
Summary
Traditional medicinal plants have been used as an alternative medicine in many parts of the world, including Ethiopia. There is no report on the anti-Quorum Sensing (Quorum Quenching, QQ) potential of traditional Ethiopian medicinal plants. The aim of this study was to evaluate selected medicinal plants from Ethiopia for their antimicrobial activities against bacterial and fungal pathogens; and to assess the interference of these plant extracts with QS of bacteria. The World Health Organization estimates that up to 80 % of the world population still relies on traditional remedies [1] with more than 35,000 plant species being used for medication purpose in various human cultures [2]. Due to its long history of practice and safety, traditional medicine has become an integral part of the Ethiopian culture. About 80 % of human population and 90 % of livestock rely on traditional medicine for treatment of diseases [5]. The emergence of antibiotic resistant microbial strains and increasing failure of the available chemotherapeutics made the search for microbiologically active medicinal plants a necessity [6]
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