Comparative study of the antimicrobial activity of native and exotic plants from the Caatinga and Atlantic Forest selected through an ethnobotanical survey

Abstract

Context: The idea that many commonly used medicinal plants may lead to the discovery of new drugs has encouraged the study of local knowledge of these resources.

Objective: An ethnobotanical survey of species traditionally used for the treatment of infectious diseases was undertaken in two areas of northeastern Brazil: one in the Caatinga (dry forest) and another in the Atlantic Forest (humid forest).

Materials: Initially, diffusion tests using paper disks and subsequently, for extracts presenting significant results (inhibition halos above 15 mm), minimum inhibitory concentrations were determined. The activity was evaluated as a percentage for each species, comparing the diameters of the inhibition halos and the number of positive results against the seven microorganisms studied. Extracts were classified into three categories: strong activity—species with halos exceeding 16 mm, moderate activity—species with halos between 13 mm and 15 mm and low activity—species with halos below 12 mm. We selected 34 species, 20 from the Caatinga and 14 from the Atlantic Forest.

Results: In the Caatinga, 50% of the 20 plant extracts studied had strong antimicrobial activity, 25% had moderate activity and 15% had low activity. In the Atlantic Forest, 28.5% of the 14 plant extracts studied showed strong activity, with 14.5% having moderate activity and 28.5% having low activity. The microorganism that was most susceptible to the extracts from the Caatinga, was Mycobacterium smegmatis; 85% of the species tested were able to inhibit its growth. The organism that was susceptible to the highest number of plant species (71%) from the Atlantic Forest was Staphylococcus aureus.

Discussion and conclusions: Extracts from the Caatinga showed a trend of superior antimicrobial activity compared to the species from the Atlantic Forest, in terms of both inhibiting a greater variety of microorganisms and demonstrating higher activity against susceptible strains.

Keywords::

• Medicinal plants
• traditional medicine
• MIC
• diffusion tests

Introduction

Plants are traditionally used to treat diseases worldwide, particularly infectious diseases and represent great potential sources of new compounds for medical use. Considering the increasing levels of bacterial resistance to many antibiotics and the subsequent need to find new antimicrobial substances, compounds isolated from plants may be able to overcome the challenges of treating drug-resistant infections (Pereira et al., 2004). There are four different methods to select medicinal plants for pharmacological studies, namely random approach, chemotaxonomy, etological and ethnodirected studies, which include ethnobotany and ethnopharmacology (Albuquerque & Hanazaki, 2006). Both of these play extremely important roles in the selection of species worthy of further studies (Monthana & Lindequist, 2005).

Some studies have evaluated the antimicrobial potential of medicinal plants in Brazil, with promising results. For instance, Machado et al. (2003) evaluated the extracts from 14 Brazilian medicinal plant used in treatment of infectious diseases and assessed their antimicrobial potential against resistant microorganisms of medical importance. The extract of Punica granatum L. (Punicaceae) was effective against methicillin-resistant Staphylococcus aureus (Machado et al., 2003). Other studies have obtained good results with plant extracts, with some extracts performing even better than the reference antibiotics used in the tests. Nascimento et al. (2000) obtained such promising results when evaluating the antibacterial activity of various extracts from plants and phytopharmaceuticals on bacteria either sensitive or resistant to antibiotics. Among the extracts tested, Syzygium jambolanum (Lam.) DC. (Myrtaceae) inhibited 57.1% of the microorganisms tested.

Brazil has numerous vegetation types, which are promising potential sources for ethnobotanical studies. Vegetation that favors humid environments is found near coastal areas, and dry environments are found in the interior of the country. In the northeast, it is possible to find two major vegetation types: Atlantic Forest and Caatinga. These regions have very significant botanical diversity, with great potential for pharmacological studies (Di Stasi et al., 2002; Albuquerque et al., 2007).

Because infectious diseases caused by bacteria and fungi frequently affect human populations due to their easy dissemination in various biological systems, studies aiming to discover more efficient and economical therapies are of most importance. Moreover, the lack of research in the Caatinga region justifies the development of studies aiming to explore the potential of its plant life. Research covering all investigative steps necessary for the discovery, evaluation, enhancement and application of antimicrobial products is extremely timely, given current needs and production demands.

In this work, species traditionally used for the treatment of infectious diseases were selected through an ethnobotanical survey in the tropical dry forest (Caatinga, municipality of Soledade, Paraiba state) and tropical wet forest (Atlantic Forest, municipality of Igarassu, Pernambuco state). The objective was to compare the potential antimicrobial activities of crude extracts from the selected species in these two regions and to assess which of them has better potential to lead to the discovery of a plant with antimicrobial properties through further pharmacological and/or phytochemical studies.

Materials

Study area

This study was conducted in two municipalities in northeastern Brazil, covering two different vegetation areas: the Caatinga and Atlantic Forest. In the Caatinga, the study was performed in the Soledade municipality, located in the Soledade microregion and in the mesoregion of Agreste, Paraíba state, at the coordinates 07°03′26′’ S and 36°21′46′’ W. Soledade is in the Paraíba River Basin and Taperoá River sub-basin (Lacerda et al., 2005), crossed by perennial rivers, but with small flow and low potential for groundwater. The seat of the Soledade municipality is 165.5 km from the capital of Joao Pessoa, 634.9 km² in area and 521 m above sea level (Mascarenhas et al., 2005). The climate is semiarid with warm summer rains (BSwh’), 7–8 months of drought and precipitation of only 400 to 600 mm per year (SEBRAE, 1998). Due to the warm and dry climate, the vegetation consists of deciduous and thorny Caatinga forests (Beltrão et al., 2005), with a dominant shrub layer and few individual trees.

In the Atlantic Forest, the municipality studied was Igarassu, located in the Itamaracá microregion and the mesoregion of Recife, Pernambuco state, at the coordinates 7°50′00′ S and 34°54′30” W, 30 km from the state capital (FIDEM, 2007). The climate is tropical, hot and humid, with rainfall in autumn and winter (As’). The average annual temperature is 25°C, and the average annual rainfall is around 2000 mm (FIDEM, 2007). The predominant vegetation includes the remnants of Atlantic Forest, scrubs, mangroves, palm trees and areas of commercial and subsistence agriculture. There are ecological reserves in the municipality, such as the Usina São José Forest Reserve (State Law n°. 9989 from 01/13/87), with dense and widespread vegetation of 323.30 hectares located on the Transcanavieira Highway (PE-41; Igarassu, 2007).

Collection of ethnobotanical data

Ethnobotanical data was collected through semi-structured interviews (Albuquerque et al., 2008). Each interview was performed with the head of family (older than 18 years) present on the occasion of the interviewer’s visit. Informed free consent terms were obtained from those who offered to participate in the study, following the legal ethical regulations set out in the 196/96 resolution from the National Health Council, Resolution 196/96. The following guiding question was used in all interviews: “What medicinal plants do you know?” Subsequently, details of each species mentioned, concerning the part used, preparation method, indications and contraindications, were recorded.

In the Caatinga, ethnobotanical data were collected in the municipality of Soledade, with sampling of all households in the communities of Cachoeira, Bom Sucesso and Barrocas, totaling 55 interviews from January to July, 2006. In the Atlantic Forest, the work was performed in the municipality of Igarassu in the community of Três Ladeiras. As a community with a high number of residents, sampling was carried out in 53% of the households, totaling 203 interviews from June 2007 to January 2008.

Species were identified after the interviews, selecting those that were used for treating infectious diseases, including diseases related to the genital/urinary tract (uterine inflammation in the ovaries or prostate, kidney or urinary tract infection), respiratory tract (bronchitis, pneumonia or throat inflammation), digestive tract (inflammation in the mouth or teeth or intestinal infection), sensory systems (inflammation in the ears or eyes), skin (furuncles or wound inflammation) and undefined inflammation.

A total of 100 species were identified in the Caatinga, with 20 species indicated for treating infectious diseases selected for the purpose of this study. In the Atlantic Forest, 14 species were selected from the 105 cited. Only those species that were mentioned by at least two interviewees were included in the sample. Species studied were identified and deposited in the Geraldo Mariz Herbarium (UFP), Federal University of Pernambuco.

Preparation of plant extracts

Tests were performed with the plant parts described by the respondents as medicinally useful, which were dried in the dark at room temperature after collection. Afterward, 20 g of plant material was crushed and sieved through 2.5 mm mesh. The resulting powder was subjected to cold extraction in 70% ethanol for 5 days. After this period, the extract was filtered with qualitative filter paper. The crude extracts were evaporated until the solvent was completely removed and was kept in a desiccator for one week. Subsequently, 20 mg of the dried extract was dissolved in 1 mL ethanol.

Antimicrobial assays

Antimicrobial activity was evaluated using two assays. Initially, diffusion tests using paper disks were performed, according to Bauer et al. (1966), with modifications. Subsequently, for extracts presenting significant results (inhibition halos above 15 mm), minimum inhibitory concentrations were determined (NCCLS, 2008).

Crude extracts were tested against standard strains of S. aureus (ATCC 6538), Bacillus subtilis (ATCC 6633), Streptococcus faecalis (ATCC 6057), Escherichia coli (ATCC 25922), Klebsiella pneumoniae (ATCC 29665), Mycobacterium smegmatis (DAUFPE 71) and Candida albicans (DAUFPE 1007), cultured in the appropriate medium for each species (Murray et al., 1995; Springfield et al., 2003). These microorganisms are among those that develop resistance to common antibiotics (Barbour et al., 2004).

The microorganisms used in the tests were kept in agar medium at 5°C. A suspension of each microorganism was prepared in sterile saline solution 24 h in advance (except for M. smegmatis, which was grown 48 h in advance), so that the colonies were tested at the apex of the growth curve, according to the standardized scale of MacFarland: 2.0 for M. smegmatis and 0.5 for the others (Murray et al., 1995). Tests were always performed in duplicate.

The microorganisms were grown in Petri dishes. Subsequently, Whatman No. 2 sterile paper disks (9 mm diameter) soaked with 50 µL of crude plant extract were deposited on the plate’s surface (Murray et al., 1995; Springfield et al., 2003). Measurements of the inhibition halos were performed after 24 h of incubation at 30°C for yeast or 35°C for bacteria. For M. smegmatis, the incubation period was 48 h.

The activity was evaluated as a percentage for each species, comparing the diameters of the inhibition halos and the number of positive results against the seven microorganisms studied. Extracts were classified into three categories: strong activity—species with halos exceeding 16 mm, moderate activity—species with halos between 13 mm and 15 mm and low activity—species with halos below 12 mm.

Determination of minimum inhibitory concentrations (MICs)

Plant extracts that showed antimicrobial activities, with inhibition halos above 15 mm, were subjected to MIC determination (Lorian, 1996). The solid medium technique was applied, using concentrations of 2000, 1500, 1000, 500, 250, 125 and 60 µg/mL, according to the recommendations of the NCCLS (2008). Tests were performed in duplicate. The following microorganisms were tested: S. aureus, B. subtilis, E. coli, M. smegmatis and C. albicans.

The MIC was defined as the lowest compound concentration that completely inhibited the growth of visible colonies of microorganisms, as compared to the control. Inhibition levels of the plant extracts when compared with the standards were taken in account, with some considered strong inhibitors (MICs up to 500 µg/mL), moderate inhibitors (MICs between 600 and 1500 µg/mL) and weak inhibitors (MICs above 1600 µg/mL; Aligiannis et al., 2001).

Results

Preliminary assessment of antimicrobial activity

Comparison of antimicrobial activity in the study areas

From the 20 plant extracts originating from Caatinga species, 18 showed activity against the microorganisms tested. Atlantic Forest species showed antimicrobial activity less frequently; of the 14 plant extracts studied, only 10 showed such activity (Table 1). For Caatinga species, 90% showed antimicrobial activity (50% high activity, 25% moderate activity and 15% low activity). In the Atlantic Forest, 71.4% of species showed activity, with 28.5% presenting strong activity, 14.5% presenting moderate activity and 28.5% presenting low activity (Table 1).

Table 1.  Comparison of the percentages of plants with antimicrobial activity from the Caatinga and Atlantic Forest in northeastern Brazil.

Parameter	Place of collection
	Caatinga	Atlantic Forest
Total of the tested species	20	14
Active percentage	90% (18)	71.4% (10)
Strong activity	50%	28.5%
Moderate activity	25%	14.5%
Low activity	15%	28.5%

In the Caatinga samples, species presenting strong inhibition (50%) stood out, followed by species that showed moderate activity (25%), while in the Atlantic Forest, species with high activity were similar in number to those with weak activity (28.5%).

Most species from the Caatinga presented activity against two or three different microorganisms, but species from the Atlantic Forest showed activity for three to five microorganisms. However, even though the species from the Atlantic Forest showed greater versatility, they did not demonstrate strong potential for inhibiting microorganisms. From all species studied in both environments, only Schinus terebinthifolius (Atlantic Forest) showed greater versatility, inhibiting five of the seven microorganisms tested: S. aureus, S. faecalis, E. coli, K. pneumoniae and M. smegmatis.

Antimicrobial screening

In the Caatinga, 85% of the species tested showed inhibition of M. smegmatis, with the exception of Ximenia americana, Myracrodruon urundeuva and Cereus jamacaru. The species that showed higher activity against this microorganism were Cnidoscolus quercifolius, Ruta graveolens, Phyllanthus sp. and Pseudobombax marginatum (Table 2). Against B. subtilis, the species that stood out with the strongest activity was Solanum agrarium, with a halo of 36 mm, followed by Anadenanthera colubrina var. cebil, M. urundeuva and P. marginatum, all with moderate activity and halos of 15 mm each (Table 2).

Table 2.  Antibacterial activity of medicinal plants from the Caatinga and Atlantic Forest, northeastern Brazil.

	Size of the inhibition zones (mm)
	Sa	Bs	Sf	Ec	Kp	Ms	Ca
Caatinga
Amburana cearensis (Allemão) A.C. Sm.	R	R	R	R	R	11	R
Anacardium occidentale L.	11	R	R	R	R	11	R
Anadenanthera colubrina var. cebil (Griseb.) Altschul.	13	15	R	R	R	21	R
Boerhavia diffusa L.	11	R	13	R	R	17	R
Cereus jamacaru DC.	R	R	R	R	R	R	R
Cnidoscolus quercifolius Pohl.	18	11	13	R	R	33	R
Cnidoscolus urens (L.) Arthur	12	12	R	R	R	15	R
Commiphora leptophloeos (Mart.) J.B.	R	R	R	R	R	15	R
Erythrina velutina Willd.	12	12	R	R	R	21	R
Maytenus rigida Mart.	15	R	R	R	R	19	R
Mentha piperita L.	12	11	R	R	R	18	R
Mimosa tenuiflora (Willd.) Poir.	13	R	R	R	R	13	R
Myracrodruon urundeuva Allemão	13	15	R	R	R	R	R
Phyllanthus sp.	15	R	R	R	R	28	R
Pseudobombax marginatum (A. St.-Hill., Juss. & Cambess.) A. Robyns	11	15	12	R	R	25	R
Ruta graveolens L.	13	13	R	R	R	28	R
Schinopsis brasiliensis Engl.	13	13	R	12	R	20	R
Sideroxylon obtusifolium (Roem. & Schult.) T.D. Penn.	R	R	R	R	R	22	R
Solanum agrarium Sendtner.	R	36	R	R	R	15	28
Ximenia americana L.	R	R	R	R	R	R	R
Atlantic Forest
Capsicum frutescens L.	12	12	R	R	R	R	R
Boerhavia diffusa L.	R	R	R	R	R	R	R
Mentha piperita L.	12	10	11	R	R	12	R
Mentha pulegium L.	R	R	R	R	R	R	R
Nectandra cuspidata Ness & Mart.	R	R	R	R	R	R	R
Ocimum basilicum L.	12	R	11	R	R	R	R
Pithecellobium cochliocarpum (Gomez) Macbr.	14	R	R	12	11	R	R
Plectranthus amboinicus (Lour.) Spreng.	17	15	12	R	R	16	R
Rosa sp.	19	12	10	R	R	11	R
Ruta graveolens L.	12	12	R	R	R	13	R
Schinus terebinthifolius Raddi	18	R	13	19	12	13	R
Solanum sp.	13	11	10	R	R	R	R
Vismia guianensis (Aubl.) Choisy	R	R	R	R	R	R	R
Xylopia frutescens Aubl.	13	14	11	R	R	17	R

Sa = Staphylococcus aureus, Bs = Bacillus subtilis, Sf = Streptococcus faecalis, Ec = Escherichia coli, Kp = Klebsiella pneumoniae, Ms = Mycobacterium smegmatis and Ca = Candida albicans. R = resistant.

Species with high activity are indicated in boldface.

A single species, S. agrarium, showed strong activity against C. albicans, with a halo of 28 mm. For E. coli, another single species from the Caatinga (Schinopsis brasiliensis) showed activity, albeit low activity, with a halo of 12 mm. From the Caatinga species, 20% showed low activity against S. faecalis, including C. quercifolius (13 mm), Boerhavia diffusa (13 mm) and P. marginatum (12 mm). Among the species studied, 70% showed activity against S. aureus, but most of them also had low activity. From these species, only one stood out with strong activity, C. quercifolius with a halo of 18 mm, followed by Maytenus rigida and Phyllanthus sp., both with moderate activity and halos of inhibition of 15 mm (Table 2).

In the Atlantic Forest, the most susceptible microorganism tested was S. aureus, which was susceptible to 71% of species, with Rosa sp. (19 mm), S. terebinthifolius (18 mm) and Mentha piperita (17 mm) considered the species that showed strong activity (Table 2). The significant antimicrobial activity of Rosa sp., popularly known as white rose, against S. aureus was particularly noteworthy. In this case, the part of the plant used to perform the test was the flower petals, which are popularly used to treat inflammation in the eyes and ears.

Another microorganism highly susceptible to Atlantic Forest species was M. smegmatis, which was inhibited by 43% species. Xylopia frutescens, with a halo of 17 mm, and M. piperita, with a halo of 16 mm, were the species considered to have strong activity (Table 2).

Only two Atlantic Forest species showed inhibition against E. coli. However, only one, S. terebinthifolius, had strong activity, with a halo of 19 mm, followed by Pithecellobium cochliocarpum with low activity and a 12 mm halo (Table 2). For B. subtilis, 50% of the species showed inhibition, but only one species reached moderate activity: M. piperita (15 mm); the other species showed low activity.

K. pneumoniae was sensitive to 14% of the Atlantic Forest species, S. terebinthifolius (12 mm) and P. cochliocarpum (11 mm; Table 2). S. faecalis was inhibited by 50% of the species tested, but all demonstrated low activity.

The two species from the Caatinga which presented no activity against the microorganisms tested were X. americana and C. jamacaru. Moreover, K. pneumoniae showed no sensitivity to the extracts tested (Table 2). Concerning the Atlantic Forest species, B. diffusa, M. pulegium, Nectandra cuspidata and Vismia guianensis showed no antimicrobial activity, and no additional species collected in the region showed activity against C. albicans (Table 2).

Comparison of antimicrobial activity of species occurring in both areas

Three species were mentioned in the interviews in both areas: B. diffusa, M. piperita and R. graveolens. B. diffusa from the Caatinga showed activity against S. aureus, S. faecalis and M. smegmatis, while plants of this species from the Atlantic Forest did not present any activity (Table 2).

The species M. piperita from the Caatinga also showed activity against S. aureus, S. faecalis and M. smegmatis, while M. piperita from the Atlantic Forest only inhibited B. subtilis. R. graveolens showed the same activity for Caatinga and Atlantic Forest plants, inhibiting S. aureus, B. subtilis and M. smegmatis, but with better results for the specimens collected in the Caatinga (Table 2).

Minimum inhibitory concentrations

MIC results are shown in Table 3. In the Caatinga, MICs were determined for 75% of the species. The extracts classified as strong inhibitors represent 22.7% of the total: C. quercifolius against S. aureus, P. marginatum against B. subtilis and R. graveolens against M. smegmatis (250 to 500 µg/mL). In 36.3% of the species, moderate inhibition was shown: Erythrina velutina against M. smegmatis and Phylanthus sp. against S. aureus (500 to 1000 µg/mL). The vast majority, 41% of species, were weak inhibitors (Table 3).

Table 3.  Minimal inhibitory concentrations of medicinal species from the Caatinga and Atlantic Forest, northeastern Brazil.

	Concentrations of µg/mL
	Sa	Bs	Ec	Ms	Ca
Caatinga
Amburana cearensis (Allemão) A.C. Sm.				1000 a 1500
Anadenanthera colubrina var. cebil (Griseb.) Altschul.		>2000		>1000
Boerhavia diffusa L.				1500 a 2000
Cnidoscolus quercifolius Pohl.	250 a 500			1000 a 1500
Cnidoscolus urens (L.) Arthur				1500 a 2000
Erythrina velutina Willd.				500 a 1000
Maytenus rigida Mart.	>2000			1500 a 2000
Mentha piperita L.				1500 a 2000
Myracrodruon urundeuva Allemão		2000
Phyllanthus sp.	500 a 1000			1000 a 1500
Pseudobombax marginatum (A. St.-Hill., Juss. & Cambess.) A. Robyns		250 a 500		>1000
Ruta graveolens L.				250 a 500
Schinopsis brasiliensis Engl.				1500 a 2000
Sideroxylon obtusifolium (Roem. & Schult.) T.D. Penn.				1000 a 1500
Solanum agrarium Sendtner.		>1000		2000	>1000
Atlantic Forest
Plectranthus amboinicus (Lour.) Spreng.	>2000	>2000		>2000
Rosa sp.	1500
Schinus terebinthifolius Raddi	250 a 500		1500 a 2000
Xylopia frutescens Aubl.				125 a 250

Note: Sa = Staphylococcus aureus, Bs = Bacillus subtilis, Ec = Escherichia coli, Ms = Mycobacterium smegmatis and Ca = Candida albicans.

Species with strong inhibition are indicated in boldface.

In the Atlantic Forest, MICs were determined for 28% of the species, and only 28.6% of these were strong inhibitors: X. frutescens against M. smegmatis (125 to 250 µg/mL) and S. terebinthifolius against S. aureus (250 to 500 µg/mL). For moderate inhibition, accounting for 14.4% of the species, Rosa sp. showed the best response against S. aureus (1500 mg/mL), and again, the vast majority (57%) of species had only a weak capacity for inhibition (Table 3).

Discussion

Comparison of antimicrobial activity in the study area

Our findings seem to indicate a pattern that needs to be better investigated and can be summarized as follows: (i) there seem to be differences in the specificity of antimicrobial activity, as the extracts from Caatinga had no effect on K. pneumoniae, and those from the Atlantic Forest had no effect on C. albicans and (ii) in general, the extracts from Caatinga plans tended to have larger halos of inhibition and greater numbers of sensitive microorganisms. One notable exception in the Atlantic Forest was S. terebinthifolius, which inhibited five microorganisms. Accordingly, the Caatinga seems to be more promising for bioprospection studies.

These differences probably reflect different biochemical strategies on the part of the plant life in response to environmental characteristics (see Vuuren, 2008). Gottlieb (1997) reports that factors such as the incidence of UV rays not only influence the formation but also the cleavage of chemical bonds of phenolic derivatives, to protect the plant against these rays. Moreover, these phenolic compounds, such as simple phenols, flavonoids, lignin and tannin, have important roles as antibiotics, natural pesticides and attractants for pollinators and in support and waterproofing. There is evidence pointing to the high occurrence of phenolic compounds in medicinal plants of the Caatinga, even contrary to some prior predictions (see Almeida et al. 2005).

Scalbert (1991) strengthened the evidence for a role for phenolic compounds by showing that tannins have the potential to inhibit the development of a wide variety of fungi. The increased activity of these plant extracts is likely due to the presence of phenolic compounds, the formation of which is favored in semiarid environments subject to high solar irradiation, such as the Caatinga. In fact, systematic studies aiming to evaluate and test the findings in other environments would be interesting.

Antimicrobial assays

Among the species tested, Anacardium occidentale was the subject of the highest number of prior studies (Laurens et al., 1992; Akinpule, 2001; Melo et al., 2006; Silva et al., 2007). Melo et al. (2006) found that the extract of A. occidentale was effective against strains of Streptococcus mitis, S. mutans and S. sanguis. The hydroalcoholic extract of A. occidentale showed significant antimicrobial activity against isolates of S. aureus from hospitalized patients, both methicillin resistant and sensitive (Silva et al., 2007). These results go against our findings; no such activity was observed in this study.

Cruz et al. (2007) investigated the antifungal effect of the aqueous extract of Sideroxylon obtusifolium (Bumelia sartorium) against C. albicans using the agar diffusion method and observed that S. obtusifolium did not present antifungal activity, as in our work.

A very interesting result in our study was the strong antimicrobial activity of 85% of Caatinga species against M. smegmatis. These results are of extreme importance, since this organism is not sensitive to most drugs and is a common cause of nosocomial infections.

In the Atlantic Forest, the species that stood out in regard to its ability to treat different infectious diseases was S. terebinthifolius. The medicinal use of this species is widespread among Brazilian traditional communities (Di Stasi et al., 2002). Degaspari et al. (2005) tested the antimicrobial activity of the alcoholic extract of the fruit of S. terebinthifolius, observing an inhibitory effect against strains of S. aureus and Bacillus cereus. Extract from the sap of S. terebinthifolius also inhibited S. aureus (Lima et al., 2006), with an activity similar to that obtained in this work. This was the only species that showed strong activity against E. coli in our study. E. coli is one of the microorganisms responsible for many cases of diarrhea in Brazil, due to deficiency of the sewage network, and treatment of patients with diarrhea usually includes antibacterial drugs, which are ineffective in some cases (Cid et al., 1996). However, the Brazilian flora has many species with activity against E. coli, as observed in a study performed on the essential oils of 29 species, in which 17 were shown to be effective (Duarte et al., 2005).

Studies with K. pneumoniae as a test organism are extremely important, because this microorganism is present in an increasingly significant number of hospital outbreaks and has undergone changes in its pattern of sensitivity to antibiotics (Santos, 2007). However, in this work, few species showed activity against K. pneumoniae, with only weak activity for two species in the Atlantic Forest, P. cochliocarpum and S. terebinthifolius.

Acknowledgments

The authors thank the communities of Três Ladeiras, Cachoeiras, Barrocas and Bom Sucesso for the participation. To CNPq for the PhD grant to CFCBR Almeida and productivity grant to UP Albuquerque. To Ana Carolina O. da Silva and Ivana Glaucia B. Cunha for technical assistance in the experiments. We also thank the contribution of the project ‘Sustainability of remnants of the Atlantic rainforest in Pernambuco and its implications for conservation and local development’, a Brazilian-German scientific co-operation within the program ‘Science and Technology for the Atlantic Rainforest’ funded by CNPq (590039/2006-7) and BMBF (01 LB 0203 A1).

Declaration of interest

The authors report no declarations of interest.