versión impresa ISSN 1517-8382
Braz. J. Microbiol. v.38 n.3 São Paulo jul./sep. 2007
Atividade antimicrobiana in vitro de extratos de folhas de Psidium guajava L. contra cepas patogênicas de importância clínica
Rathish Nair; Sumitra Chanda*
Phytochemical, Pharmacological and Microbiological Laboratory, Department of Biosciences, Saurashtra University, Rajkot, Gujarat, India
The methanol, acetone and N, N-dimethylformamide (DMF) fractions of leaves of Psidium guajava L. were evaluated for antibacterial and antifungal activity. Piperacillin and gentamicin were used as standards for antibacterial assay, while nystatin and flucanazole were used as standards for antifungal assay. 91 clinically important strains were used for the study which were both clinical isolates as well as identified strains. The antibacterial activity was more pronounced against gram-positive bacterial and fungal strains. Moderate activity was shown against the gram-negative bacterial strains studied.
Key-words: Antibacterial, antifungal, Psidium guajava extracts, clinical isolates.
Os extratos de folhas de Psidium guajava L. preparados com metanol, acetona e N,N-formamida foram avaliados quanto a sua atividade antibacteriana e antifúngica. Piperacilina e gentamicina foram empregadas como padrões de atividade antibacteriana e nistatina e fluoconazol com padrões de atividade antifúngica. O estudo foi desenvolvido com noventa e uma cepas de importância clínica, incluindo isolados clínicos e cepas identificadas. A atividade antibacteriana foi mais intensa contra as cepas de bactérias Gram positivas e de fungos. A atividade contra bactérias Gram negativas foi moderada.
Palavras-chave: antibacteriano, antifúngico, extrato de Psidium guajava, isolados clínicos.
Since ancient times, plants have been a veritable source of drugs; man tends to ignore the importance of herbal medicine (1). Research work on medicinal plants is intensified and information on these plants be exchanged. This thought will go a long way in the scientific exploration of medicinal plants for the benefit of man and is likely to decrease the dependence or importance of drugs (2). The boiled water extract of guava plant leaves and bark are used in medicinal preparations which are utilized as remedies for dysentery, diarrhoea and upper respiratory tract infections while guava fruit paste and cheese are popular dishes in Florida, the West Indies and parts of South America (3) In Malaysia, Psidium gujava is used for stomach ache and gastroenteritis (4-6); Leaf, root, and bark extracts are used for treatment of diarrhoea, leukorrhea, cholera, external ulcers, and skin diseases (7). Guajava leaf extract contains guajava polyphenol (8) that has an anti-oxidation action (9). The flower and leaf of the plant have been reported to have antibiotic activity (10). In the present study antimicrobial potentiality of the P. guajava leaves was investigated against a few clinically isolated as well as standard microbial cultures.
MATERIALS AND METHODS
Psidium guajava L. (Myrtaceae) leaves were collected in February, 2005 from Rajkot in the State of Gujarat (Western India). The taxonomic identification of the plant was confirmed by Dr. P. S. Nagar of the Department of Biosciences, Saurashtra University, Rajkot.
Leaves of P. guajava were collected air dried and then powdered in a homogenizer and 10 grams were used for different solvent extraction (Methanol, Acetone, N, N-dimethylformamide). In solvent extraction, the sample was extracted in solvent kept on a rotary shaker overnight, and then the filtrate was collected and centrifuged at 5000 rpm. The solvent was then evaporated to dryness under reduced pressure and the extracted compound was used for the antimicrobial assay. The percentage yield of methanol, acetone and N, N-dimethylformamide (DMF) are 14.92, 9.38 and 23.07 respectively.
Gram-positive and Gram-negative bacteria and fungi (listed in Table 1) were obtained from National Chemical Laboratory (NCL), Pune and Spandan diagnostic and Microcare diagnostic laboratory, Rajkot.
Preparation of samples
Methanol, acetone and DMF extracts were dissolved in DMSO at a concentration of 25 mg/ml and 12.5 mg/ml respectively and used as working stocks. Sterile discs (Hi-media Labs) were impregnated with 20 µl of the stock solution. Gentamicin and piperacillin for bacteria; nystatin and fluconazole (Himedia Labs) for fungus were used as standards for comparative studies.
Antimicrobial activity was performed by disc diffusion method (11). The bacterial strains were grown in nutrient broth while fungal strains were grown in MGYP (Malt glucose yeast peptone) broth. Mueller Hinton agar no. 2 was the media used to study the antibacterial susceptibility while Sabroaud agar was used to study the antifungal susceptibility test. The cultures were grown for 24 hours, and the turbidity of the culture was maintained according to the 0.5 MacFarland standards. The inoculum's size was 1 X 108 cells.
In the present study P. guajava leaf extracts extracted in methanol (PME), acetone (PAE) and N, N-dimethylformamide (DMF) (PDE) were investigated at two different concentrations for their antimicrobial potentiality against 91 clinically important microbial strains. PME-500 was active against 70% of the total gram-positive bacteria studied, while PAE-500 and PDE-500 were active against 80 and 50 percent of the studied gram-positive bacteria respectively. All the three extracts showed similar activity profiles against gram-negative bacterial strains studied. They were active against 76.36% of the total gram-negative bacteria studied which included 73.68% Pseudomonas spps., 93.75% E. coli, 83.33% Klebsiella spps. and 66.66% of Proteus spps. All of the extracts were inactive against one of the three Citrobacter spps. and Alcaligenes fecalis, while they were active against Salmonella typhimurium. The three extracts showed varying results against the fungal strains. PME-500 was active against 37.5%, PAE-500 was active against 56.25% and PDE-500 was active against 31.25% of the total fungal strains studied. All the extracts were inactive against the three Aspergillus spps. studied. Details of the result are shown in Table 2.
All the three extracts of P. guajava showed dose dependent activity. Acetone extract was highly active against gram positive and fungal strains while all of the extracts were equally active against gram-negative strains. From the results, it is concluded that acetone extract of Psidium guajava is highly active against 74.72% of the total 91 microbial strains studied. The acetone extract of P.guajava should further be studied for its phytochemical constituents in order to elucidate the active principle within the extract which can turn out to be a novel antimicrobial agent of the future.
Financial support from Department of Special assistance (DSA) project, New Delhi and supply of clinical isolates by Micro Care and Spandan Diagnostic Laboratories, Rajkot are gratefully acknowledged.
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Submitted: October 03, 2006; Approved: July 16, 2007
* Corresponding Author: Mailing address:Phytochemical, Pharmacological and Microbiological Laboratory, Department of Biosciences, Saurashtra University, Rajkot-360005, Gujarat, India. E-mail: firstname.lastname@example.org