Abstract

In an effort to document the antibacterial properties of plants commonly used by the people of Puerto Rico, we studied the effects of 172 plant species, utilizing the disc diffusion method, against Escherichia coli and Staphylococcus aureus. The methanolic extracts of 14 species showed antibacterial activities during this preliminary screen. These positive plant extracts were tested successively over 15 additional species. The results showed that extracts from Citrus aurantifolia (Rutaceae), Citrus aurantium (Rutaceae), Punica granatum (Punicaceae), Phyllanthus acidus (Euphorbiaceae) and Tamarindus indica (Caesalpiniaceae) possess strong in vitro antibacterial activity against the bacteria tested.

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Keywords: Plant antibacterials; Antibacterial plants from; Puerto Rico; Tropical plants; Antimicrobials

Introduction

Exploring the healing power of plants is an ancient concept. For many centuries people have been trying to alleviate and treat diseases with different plant extracts and formulations (Cowan, 1999). It is estimated, however, that of the 250,000-500,000 species found on Earth, only 1% have been studied for their pharmaceutical potential. In Puerto Rico, the use of plants for medicinal purposes is a common practice, especially among adults living in the countryside. Many plants of our flora are known to possess antimicrobial properties and have been used by the local population in many instances to treat colds, coughs, bronchitis, diarrhea, respiratory infections, urinary disorders and skin lesions (Hernandez et al., 1984). In the past, other groups have published important ethnobotanical bibliographies that compiled and described the most frequently used species to treat infections (Liogier, 1990; Nunez-Melendez, 1989; Morton, 1981). However, scientific evidence confirming that these traditional remedies possess antibiotic properties is lacking.

Over the years there have been several studies documenting the antibacterial properties of plants from other regions of the Caribbean and South America (Chariandy et al., 1999; Anesini and Perez, 1993; Martinez et al., 1996; Caceres et al., 1993; Rojas-Hernandez et al., 1978a; Rojas-Hernandez et al., 1978b). The Traditional Medicine in the Islands (TRAMIL) research project series started in 1982 in Haiti, and has documented a great deal of information concerning the medicinal use of plants in the Caribbean basin (Robineau and Soejarto, 1996). In Puerto Rico, Guerrero and Robledo (1993) studied the effects of some endemic plants; and more recently (Frame et al., 1999) examined the anti-Mycobacterium tuberculosis effects of 50 local plants.

In Puerto Rico, as in many other countries, we are unfortunately at risk of losing the ancestral knowledge of the healing properties of plants. In an effort to corroborate, document, and expand the traditional use of medicinal plants with antibacterial properties in Puerto Rico, we collected and evaluated the antibacterial effects of a vast number of species against different types of Gram-positive and Gram-negative bacteria.

Materials and methods

Plant collection

Between March 1983 and March 1985, 172 species of tropical plants, from 73 different families, were collected from their natural habitats in the north-western and western regions of Puerto Rico, specifically in the municipalities of Isabela, Aguadilla, Quebradillas, San German and Sabana Grande. A specimen of each species was dry-mounted, photographed and preserved...