Evaluation of the antibacterial activity and toxicity of Myrciaria caulifloria methanolic leaf and fruit extracts

摘要

Methanol extracts from M. caulifloria leaves and fruit were tested for antimicrobial activity and toxicity in vitro. M. caulifloria leaf extract inhibited the growth of 9 of the 14 bacteria tested (64%) whilst the fruit extract inhibited the growth of 11 of the 14 bacteria tested (79%). Both Gram-positive and Gram-negative bacterial growth were inhibited by M. caulifloria leaf and flower extracts. 7 of the 10 Gram-negative bacteria (70%) and 2 of the 4 Gram-positive bacteria (50%) tested had their growth inhibited by M. caulifloria leaf extract whereas the fruit extract inhibited 7 of the 10 Gram-negative bacteria (70%) and 100% of the Gram-positive bacteria tested. M. caulifloria leaf extract proved to be toxic in the Artemia fransiscana bioassay with 24, 48 and 72h LC50’s of 232.9 ± 36.3 μg/ml, 169.1 ± 11.5 μg/ml and 128.1 ± 5.6 μg/ml respectively, making it more toxic than Mevinphos (24, 48 and 72h LC50’s 1346.0 ± 78.2 μg/ml, 505.3 ± 37.7 μg/ml, 103.9 ± 12.8) at all time points except 72h but less toxic than potassium dichromate (24, 48 and 72h LC50’s 86.3 ± 5.1 μg/ml, 80.4 ± 4.3 μg/ml, 77.9 ± 4.9). M. caulifloria fruit extract was non-toxic in the Artemia fransiscana bioassay indicating its potential as an antibacterial agent for medicinal use. Introduction Bacterial resistance to currently used antibiotics is becoming a concern to public health (Monroe and Polk, 2000). The development of bacterial super resistant strains is resulting in currently used antibiotic agents failing to end many bacterial infections. For this reason the search is ongoing for new antimicrobial agents, either by the design and synthesis of new agents, or through the search of natural sources for as yet undiscovered antimicrobial agents (Bhavnani and Ballow, 2000). The antiseptic qualities of medicinal plants have been long recognised. Recently there has been a revival of interest in herbal medications (Chariandy et al., 1999) due to a perception that there is a lower incidence of adverse reactions to plant preparations compared to synthetic pharmaceuticals. Myrciaria cauliflora (Mart.) O.Berg. (commonly known as jaboticaba) is a small evergreen tree of the family Myrtaceae. It is native to Brazil and the West Indies. M. cauliflora is grown extensively in Minas Gerais region near Rio de Janiero in Southern Brazil for the small (3-4cm diameter) tough skinned purple grape-like fruit it grows along its branches. The fruit has a thick purple skin covering a sweet, white or rosy pink gelatinous flesh containing 1 – 4 seeds. The fruit have a pleasant flavour and are commonly eaten fresh or used to produce jams, strong wines, and liqueurs. M. cauliflora also has a history of use as a traditional medicine for the treatment of numerous ailments. The skin is used to produce an astringent decoction which has been used in the treatment of a wide variety of ailments including diarrhoea, asthma and haemoptysis (Morton, 1987). Gargling the decoction has also been used to relieve chronic inflammation of the tonsils (Morton, 1987). Despite its range of traditional medicinal uses, the phytochemistry and therapeutic potential of M. cauliflora has not been extensively studied. M. cauliflora has been reported to contain tannins (Morton, 1987), cyanidin 3-glucoside (Einbond et al., 2004) and peonidin 3-glucoside and its aglycone (Trevisan et al., 1972). In his recent doctoral thesis, Reynertson (2007) identified a novel depside (jaboticabin) and 16 other known compounds from crude methanolic extracts from M. cauliflora fruit. This report highlighted the two depsides jaboticabin and 2-O-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxyphenylacetic acid as being of particular therapeutic potential due to their ability to inhibit cytokine production, their cytotoxicity towards HT29 and HCT116 colon cancer cell lines and their antioxidant activity. Surprisingly, the antiseptic properties of M. cauliflora remain largely unstudied. The antibacterial and antifungal properties of other m