Antiviral and antimicrobial activities of Colombian medicinal plants

Strong antiviral and antimicrobial activities were detected in methanolic extracts of 24 plants used medicinally in the treatment of skin infections in four different regions of Colombia. Thirteen extracts displayed activity against herpes simplex virus (HSV) whereas none was active against poliovirus. The antiviral activity was indicated by a total inhibition of viral cytopathic effects (CPE) at a non-cytotoxic concentration of the extract. The most potent extract was obtained from Byrsonima verbascifolia (L.) HBK. which showed anti-HSV activity at a concentration as low as 2.5 microg/ml. Antimicrobial screening was conducted using the disc diffusion assay against Klebsiella pneumoniae, Escherichia coli, Streptococcus faecalis, Mycobacterium phlei, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella typhimurium and the human pathogenic yeast, Candida albicans. Anti-Candida activity was observed for Piper lanceaefolium HBK. and Juglans neotropica Diels. Twenty-two extracts displayed activity against Gram-positive bacteria whereas none was active against the Gram-negative species. We concluded that these Colombian medicinal plants represent an untapped source of potentially useful antivirals and are worthy of further study.     

Direct and indirect antimicrobial effects and antioxidant activity of Cordia gilletii De Wild (Boraginaceae)

Cordia gilletii De Wild (Boraginaceae) root bark is traditionally used in Democratic Republic of Congo (DRC) for the treatment of various disorders, including malaria, diarrhea, wounds and skin diseases; part of these activities may rely on antimicrobial and antioxidant properties. Successive extracts of root barks powder with n-hexane, dichloromethane, ethyl acetate, methanol and water were tested for antimicrobial activity, both direct and indirect (antibiotic resistance reversal), against 10 strains of bacteria and 1 strain of fungi by broth microdilution and agar diffusion methods. The eventual synergy between plant extracts and antibiotics was investigated by the determination of the fractional inhibitory concentration index (FIC index). The methanol extract showed direct antimicrobial activity against all tested microorganisms with minimum inhibitory concentrations (MIC) ranging between 125 and 1000 microg/ml, whereas the ethyl acetate and the dichloromethane extracts showed activity on four and three strains, respectively. 200 microg/ml of n-hexane and dichloromethane extracts decreased the MICs of penicillin and streptomycin 4-64-fold for methicillin-resistant Staphylococcus aureus. A synergistic effect was found between the methanol extract and tetracycline, whereas additive effects were observed for the other combinations tested. The methanol and dichloromethane extracts showed the greater antioxidant activity by scavenging the free radical DPPH with IC(50) values of 3.2 and 8.1 microg/ml, respectively. These results support the use of the plant in the treatment of infectious diseases and wounds; they warrant further studies as to the nature of active compounds.     

Antimicrobial activity of plants used in traditional medicine of San Juan province, Argentine

Eighteen extracts from Acaena magellanica, Baccharis grisebachii, Ephedra breana, Oxalis erythrorhiza, Pachylaena atriplicifolia and Satureja parvifolia were assessed for antimicrobial activity against bacteria and fungi with the agar dilution method. The hexane (H) and dichloromethane (DCM) extracts of B. grisebachii and O. erythrorhiza showed the broadest spectrum of action against fungi, inhibiting all of the tested dermatophytes with MICs ranging from < or =25 to < or =1000 microg/ml. Trichophyton rubrum was the most susceptible species and Cryptococcus neoformans was inhibited only by the DCM extract of B. grisebachii with MIC of 600 microg/ml. Regarding the antibacterial activity, H and DCM extracts of B. grisebachii as well as the DCM of O. erythrorhiza, were active on methicillin-resistant and methicillin-sensitive Staphylococcus aureus with MIC from < or =125 to < or =500 microg/ml. The DCM extract of B. grisebacchii was more active against methicillin-resistant than methicillin-sensitive strains.     

Antimicrobial activity of terpenoids from Trichodesma amplexicaule Roth

T. amplexicaule Roth. has been investigated phytochemically for biologically active constituents from the benzene extract. This yielded a mixture of terpenoids: beta-sitosterol, alpha-amyrin, lupeol, hexacosanoic acid, ceryl alcohol and hexacosane. The sequential extracts, isolated terpenoids and reference antibiotics were screened for their possible bioactivities against selected pathogenic bacteria, Escherichia coli, Staphylococcus aureus and fungi, Aspergillus flavus and Penicillium chrysogenum etc. Out of the sequential extracts, the benzene extract was more potent against S. aureus (IZ = 10.36) and R. phaseoli (IZ = 10.69). The inhibition zones of isolated terpenoids were also recorded and the activity index was calculated and it was found that hexacosane was more active (IZ = 13.39) against E. coli and hexacosanoic acid had greater activity against A. flavus (IZ = 11.56). The present study deals with antimicrobial screening of sequential extracts and isolated terpenoids.     

Evaluation of the antimicrobial potential of medicinal plants from the Ivory Coast

A total of 148 crude ethanol extracts from 115 plant species were tested in vitro against Gram-negative strains (Escherichia coli, Pseudomonas aeruginosa) and the Gram-positive Staphylococcus aureus and Enterococcus faecalis. Moreover, they were submitted to antifungal assays against Candida albicans and Cladosporium cucumerinum, a human and a plant pathogenic microorganism, respectively, known to be good indicators of antifungal activity. No activity was detected against the Gram-negative bacteria, while 14.8% and 10.8% of the extracts showed Gram-positive bactericidal or bacteriostatic effects on S. aureus and E. faecalis, respectively. An antifungal activity was observed with 15 extracts (10.1%). Two species were particularly active against the fungi: Dioscorea minutiflora and Erythrina vogelii. The young tubers of D. minutiflora contain metabolites with a specific effect on fungi and were not active against the bacteria. On the other hand, E. vogelii was highly effective against the Gram-positive bacteria and the fungi.     

Antimicrobial activity of Alstonia macrophylla: a folklore of bay islands

The methanolic crude and methanol-aqueous extract of Alstonia macrophylla leaves and n-butanol part of the crude extract showed antimicrobial activity against various strains of Staphylococcus aureus, Staphylococcus saprophyticus, Streptococcus faecalis, Escherichia coli, Proteus mirabilis, Trichophyton rubrum, Trichophyton mentagrophytes var. mentagrophytes and Microsporum gypseum. The minimum inhibitory concentration (MIC) values ranges from 64 to 1000 microg/ml for bacteria and 32-128 mg/ml for dermatophytes. However, the strains of Pseudomonas aeruginosa, Klebsiella sp. and Vibrio cholerae showed resistance against in vitro treatment of the extracts up to 2000 microg/ml concentration, while the two yeast species were resistant even at 128 mg/ml concentration. The stem bark extract prepared similarly was found to be less active compared to the leaves. Phytochemical study indicates that the crude extract contains tannins, flavonoids, saponins, sterols, triterpene and reducing sugars. Further fractionation and purification of n-butanol part of the extract showed the presence of beta-sitosterol, ursolic acid, beta-sitosterol glucoside and a mixture of minor compounds only detected in TLC.     

Evaluation of the antimicrobial property of the stem bark of Picralima nitida (Apocynaceae)

The basic fraction (BF) of the methanol extract of the stem bark of Picralima nitida (family Apocynaceae) exhibited significant antimicrobial activity against a wide range of Gram-positive bacteria and fungi, but limited activity against Gram-negative bacteria. The BF had a similar minimum inhibitory concentration (MIC) for S. aureus to the control drug ampicillin, and lower MIC values against A. flavus and A. niger than those of tiaconazole. Values of the minimum bactericidal concentration (MBC) of the BF against microorganisms tested were generally much higher than those for the control drugs ampicillin and gentamicin. The results suggest that some constituents of the stem bark could be isolated and developed into effective antimicrobial agents.     

Antitumor, antioxidant and antimicrobial activities of Bersama engleriana (Melianthaceae)

The aim of this study was to evaluate the antitumor, antioxidant and antimicrobial activities as well as the phytochemical composition and the acute toxicity of the methanolic extracts from the roots (BER), stem bark (BEB), leaves (BEL) and wood (BEW) of Bersama engleriana. The crown gall tumor and DPPH radical scavenging assays were used to detect respectively the antitumoral and oxidant activities. Agar diffusion and liquid dilution were used for antimicrobial tests and the phytochemical assays were conducted according to Harbone methods. The single-dose oral toxicity test was performed in accordance with the OPPTS 870.1100 and OECD 401 guidelines. The phytochemical tests indicated the presence of flavonoids, phenols, triterpenes and anthraquinones in all extracts. Pronounced tumor reducing activity was observed with the extracts from the roots (69.32%) and leaves (65.42%). The DPPH scavenging activity showed that the extract from the leaves was the most active with 93.71% inhibition rate at the 1000 microg/ml. The results of antimicrobial activity showed that all tested extracts were active against all tested microbial species, including Gram-positive, and negative bacteria, the two Candida species and mycobacteria. The MIC values obtained ranged from 9.76 to 156.25 microg/ml. Under the conditions of the studied toxicity, all extracts were found to be non-toxic. The overall results of this study indicates that the extracts from the roots, stem bark, leaves and wood have interesting antioxidant properties and represent a potential source of medicine for the treatment of infectious diseases and cancer.     

Antimicrobial, antioxidant, antitumour-promoting and cytotoxic activities of different plant part extracts of Garcinia atroviridis griff. ex T. anders

Crude extracts (methanol) of various parts, viz. the leaves, fruits, roots, stem and trunk bark, of Garcinia atroviridis were screened for antimicrobial, cytotoxic, brine shrimp toxic, antitumour-promoting and antioxidant activities. The crude extracts exhibited predominantly antibacterial activity with the root extract showing the strongest inhibition against the test bacteria at a minimum inhibitory dose (MID) of 15.6 microg/disc. Although all the extracts failed to inhibit the growth of most of the test fungi, significant antifungal activity against Cladosporium herbarum was exhibited by most notably the fruit (MID: 100 microg), and the leaf (MID: 400 microg) extracts. None of the extracts were significantly cytotoxic, and lethal towards brine shrimps. The root, leaf, trunk and stem bark extracts (except for the fruits) showed strong antioxidant activity exceeding that of the standard antioxidant, alpha-tocopherol. Antitumour-promoting activity (>95% inhibition) was shown by the fruit, leaf, stem and trunk bark extracts.     

Antimicrobial activities of Barringtonia acutangula

Crude extracts and VLC fractions from the stem bark of Barringtonia acutangula (L.) Gaertn (Fam. Lecythidaceae) were screened for their antimicrobial activities against two Gram-positive bacteria, two Gram-negative bacteria and two fungi using a microdilution titre assay. Among the crude extracts, petroleum ether extract showed good activity against all test organisms. The VLC fraction PE 16 was found to be very effective against Bacillus subtilis (MIC=25 microg/ml) and Aspergillus niger (MIC=12.5 microg/ml). The activities were compared to standard antibiotics-kanamycin and fluconazole. The major compound from PE16 was identified as 12, 20(29)-lupadien-3-ol by NMR spectroscopy.     

药用植物车前内生真菌分离及其抑菌活性初步分析

目的：研究药用植物车前可培养内生真菌多样性及其抑菌活性特征。方法：通过组织块法对内生真菌进行分离,并选择小麦全蚀病菌、枸杞黑果病菌、番茄灰霉病菌、黄瓜枯萎病菌和黄瓜立枯病菌5 种植物病原真菌和枯草芽孢杆菌、大肠杆菌、金黄色葡萄球菌和铜绿假单胞菌4 种细菌作为指示菌,采用对峙法和改进的菌块法测定抑菌活性。结果：从车前根茎叶组织器官中分离出13 株内生真菌,以茎部最多,叶部次之,根部最少;经形态学初步分类鉴定归于2 个目,2 个科,5 个属;其中有11 株菌对1 种或多种植物病原真菌指示菌有不同程度的抑制作用,占菌株总数的84.6%,6 株内生真菌对1 种或多种供试细菌指示菌具有不同程度的抑制作用,占分离菌株总数的46.2%;3 株活性菌株PAEFS001、PAEFS007、PAEFS008 分别对5 种供试植物病原真菌指示菌具有明显抑制作用,菌株PAEFS001 属于束丝菌属,菌株PAEFS007 和PAEFS008 同属于曲霉属;1 株活性菌株PAEFS003 分别对枯草芽孢杆菌和金黄色葡萄球菌2 种供试细菌指示菌有明显的抑制作用,属于梭孢霉属;药用植物车前内生真菌具有明显的抑菌活性,抑制植物病原真菌的范围较宽,对革兰氏阳性菌枯草芽孢杆菌和金黄色葡萄球菌的抑制作用明显,具有一定的选择性。结论：从药用植物车前内生真菌寻找新的抑菌活性物质是可行的,通过对其进行开发和利用,对提高药用植物车前的综合利用价值具有重要意义。     

Antimicrobial activity of selected Peruvian medicinal plants

The antimicrobial activity of 36 ethanol extracts from 24 plants, all of them currently used in the Peruvian traditional medicine for the treatment of several infectious and inflammatory disorders, was tested by means of the agar-well diffusion assay against four bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) and four fungi (Candida albicans, Trichophyton mentagrophytes, Microsporum gypseum and Sporothrix schenckii). Twenty-five (69%) extracts showed some degree of antimicrobial activity against at least one microorganism. The plants with the greatest antimicrobial activity were Cestrum auriculatum L. Heritier (Solanaceae), Iryanthera lancifolia Ducke Suesseng (Myristicaceae), Lepechinia meyenii (Walp.) Epling (Lamiaceae) and Ophryosporus peruvianus (Gmelin) King & H. Rob. (Asteraceae).     

Screening for anti-infective properties of several medicinal plants of the Mauritians flora

Several plants of the Mauritian flora alleged to possess anti-infective properties were studied against different strains of pathogenic bacteria and fungi. The grounded dried plant materials were extracted with different extractants and screened for anti-microbial activity using the disk diffusion and the micro-dilution techniques. Preliminary screening revealed that the methanol extracts were most active. Salmonella enteritidis, Enterobacter cloacae and Bacillus subtilis were the three test organisms, which were found to be susceptible to all the crude methanolic extracts of the different plants investigated (100% susceptibility), followed by Escherichia coli (57.1%) and Pseudomonas aeruginosa (57.1%), and Staphylococcus aureus (28.6%). The lowest minimum inhibitory concentration recorded for the different crude methanol extracts against Staphylococcus aureus, Escherichia coli, Salmonella enteritidis, Enterobacter cloacae, Bacillus subtilis and the mould fungus Candida albicans were 500, 1000, 125, 250, 1000 and 125 micro g/ml, respectively. Bioautography using Cladosporium cucumerinum revealed that dichloromethane (DCM) extracts had the highest activity against the phytopathogenic fungus. It was also noted that the DCM extracts of Michelia champaca and Antidesma madagascariense yielded the maximum number of growth inhibiting compounds against Cladosporium cucumerinum. Activity of the different crude extracts was also investigated against several phytopathogenic filamentous fungi, Colletotrichum glocosporoides, Rhizoctonia solani, Sclerotinia sclerotium, Guignardia sp. and Fusarium oxysporum. It was found that crude hexane extracts as well as crude DCM extracts exhibited marked activity against several strains of fungi, especially Colletotrichum glocosporoides, Sclerotinia sclerotium and Guignardia sp.     

Antimicrobial activity of some important Adiantum species used traditionally in indigenous systems of medicine

Adiantum Linn. of Adiantaceae family is one of the most common and widely distributed species. Ethnomedicinally, the genus is important and popularly known as "Hansraj" in Ayurvedic System of Medicine. It has been used in cold, tumors of spleen, liver and other viscera, skin diseases, bronchitis and inflammatory diseases. It is also considered as tonic and diuretic. In the present study its four important species, i.e. Adiantum capillus-veneris, Adiantum peruvianum, Adiantum venustum and Adiantum caudatum were collected and extracted with methanol. These extracts were tested for their antimicrobial agents against five gram positive, six gram negative (including multiresistant bacteria Staphylococcus aureus) and eight fungal strains using standard microdilution assay. The maximum activity was exhibited by the methanolic extract of Adiantum venustum followed by Adiantum capillus-veneris, Adiantum peruvianum and Adiantum caudatum. The methanolic extract of Adiantum capillus-veneris had very low MIC value (0.48 microg/ml) against Escherichia coli whereas, Adiantum venustum extract against Aspergillus terreus with MIC of 0.97 microg/ml. Total phenolic constituents of Adiantum species viz. Adiantum venustum, Adiantum capillus-veneris, Adiantum peruvianum and Adiantum caudatum were 0.81% (w/w), 0.83% (w/w), 0.71% (w/w) and 0.52% (w/w), respectively (as gallic acid equivalent); implying that the observed activity could be related to the amount of phenolics.     

Antibacterial, anti-inflammatory, anti-cholinesterase and mutagenic effects of extracts obtained from some trees used in South African traditional medicine

Extracts obtained from 10 trees used in South African traditional medicine were screened for antibacterial, anti-inflammatory (COX-1 and COX-2) and anti-cholinesterase activities and investigated for potential mutagenic effects using the Ames test. Antibacterial activity was detected using the disc-diffusion and micro-dilution assays. The extracts were tested against Gram-positive bacteria: Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus and Gram-negative bacteria: Escherichia coli and Klebsiella pneumoniae. Of the 78 different plant extracts investigated, 80% showed activity against both Gram-positive and Gram-negative bacteria in the disc-diffusion assay. In the micro-dilution assay, 60% of the plant extracts showed minimum inhibitory concentration (MIC) values < or =1.56 mg ml(-1). The lowest MIC value (0.092 mg ml(-1)) was recorded for an ethyl acetate root extract of Acacia sieberiana against Staphylococcus aureus and Escherichia coli. In the anti-inflammatory assay, 70% of the investigated plant extracts (0.25 mg ml(-1)) inhibited both COX-1 and COX-2 activity (>50% and 70% for water and organic solvent extracts, respectively). An ethyl acetate leaf extract of Trichilia dregeana showed selective inhibition of COX-2 (81%). In the acetylcholinesterase inhibitory test, 21% of the plant extracts were active at a concentration < or =1 mg ml(-1) using the micro-dilution assay. The lowest IC(50) value was 0.04 mg ml(-1) obtained with an ethanol bark extract of Combretum kraussii. None of the investigated plants showed any potential mutagenic effects.     

Antibacterial activities of medicinal plants used for the treatment of diarrhoea in Limpopo Province, South Africa

The ethnobotanical survey conducted in this study showed that 21 plant species belonging to 14 families are used in traditional medical practice in Limpopo Province, South Africa, for the treatment of diarrhoea. Methanol, ethanol, acetone and hot water extract from different plant parts (leaves, roots, bark and stem rhizome), of several of these plants (Indigofera daleoides, Punica granatum, Syzygium cordatum, Gymnosporia senegalensis, Ozoroa insignis, Elephantorrhiza elephantina, Elephantorrhiza burkei, Ximenia caffra, Schotia brachypetala and Spirostachys africana), were screened for antibacterial activity against Vibro cholera, Escherichia coli and Staphylococcus aureus, Shigella spp., Salmonella typhi. The antibacterial activity was determined by agar-well diffusion method and expressed as the average diameter of the zone of inhibition of bacterial growth around the wells. The minimum inhibitory concentration (MIC) of active extracts was determined by using the micro-plate dilution assay. Most of the extracts showed relatively high antibacterial activity against most of the tested microorganisms with the diameter of inhibition zones ranging between 10 and 31 mm. Of the plants studied, the most active extracts were those obtained from Punica granatum and Indigofera daleoides. All extracts from two plants, namely, Punica granatum and Ozoroa insignis, were active against all bacterial strains while only organic extracts of Indigofera daleoides inhibited the growth of all tested microorganisms. Water extract of Punica granatum were equally active as organic extracts against bacteria such as Staphylococcus aureus, Shigella sonnei and Shigella flexneri. All extracts of Elephantorrhiza elephantina, Elephantorrhiza burkei and Ximenia caffra and Schotia brachypetala were not active against Escherichia coli and Salmonella typhi. The MIC values for active extracts ranged between 0.039 and 0.6 mg/ml. The results obtained appeared to confirm the antibacterial potential of the plants investigated, and their usefulness in the treatment of diarrhoea.     

In vitro antimicrobial activity of plants used in Cambodian traditional medicine

The purpose of the present study was to screen 27 plant species used in the traditional medicine of Cambodia for in vitro antibacterial and antifungal activities. Thirty-three methanolic extracts were tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Mycobacterium smegmatis and Candida albicans. Screened by disk diffusion assay, the extracts showed antimicrobial activity especially on Gram-positive bacteria. None of the crude methanolic extracts showed activity against P. aeruginosa. Twenty-five selected extracts were evaluated using a micro-dilution test. Harrisonia perforata (roots) and Hymenodictyon excelsum (bark) exhibited a bactericidal effect against S. aureus at a concentration of 500 microg/ml. Azadirachta indica (bark), Harrisonia perforata (roots and stem) and Shorea obtusa (roots) exhibited a bactericidal effect against M. smegmatis at 250 microg/ml.     

Investigations of antimicrobial activity of some Cameroonian medicinal plant extracts against bacteria and yeast with gastrointestinal relevance

Ethnopharmacological relevance

Resistance against antibiotics of many bacteria is accumulating. Therefore, searches for new substances with antimicrobial activity have become an urgent necessity. Medicinal plants are frequently used in popular medicine as remedies for many infectious diseases (intestinal infection, malaria, tuberculosis, etc.).

Aim of the study

This study aimed to determine the in vitro antimicrobial activity of hexane, ethyl acetate and methanol extracts from different parts (leaves, stem bark, entire plant) of five different plant species against bacteria and yeast of gastrointestinal relevance.

Material and methods

Twenty-one extracts from all the following plants (Albizia gummifera (leaf), Ficus exasperata (leaf and stem bark), Nauclea latifolia (leaf and stem bark), Ricinodendron heudelotii (stem bark), Senna hirsuta (entire plant) have been screened for their antimicrobial activity against eight bacteria species including Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus), Gram-negative bacteria (Escherichia coli, Shigella dysenteriae, Shigella flexneri, Salmonella typhi, Pseudomonas aeruginosa, and Klebsiella pneumoniae) and one yeast species (Candida albicans) using agar disc-diffusion, and microbroth dilution assays.

Results

Results demonstrated that F. exasperata and N. latifolia were active against the whole set of tested microorganisms. The methanol extract of N. latifolia (leaf and stem bark) was the most active against against C. albicans, E. coli, S. aureus, P. aeruginosa with a minimum inhibitory concentration (MIC) of 2, 32, 64 and 64 μg/ml, respectively. The methanol extract of leaf of F. exasperata was also most active with significant inhibitory activity against E. coli, S. dysenteriae, S. Typhi and P. aeruginosa with MIC values of 128 μg/ml. Only the extract of N. latifolia (stem bark and leaf) showed anticandidal property.

Conclusion

The results show that these plant extracts exhibit antimicrobial activity and N. latifolia proved to be most effective as an antibacterial and antifungal.     

Evaluation of the flora of northern Mexico for in vitro antimicrobial and antituberculosis activity

The aim of the present study was to evaluate the potential antimicrobial activity of 14 plants used in northeast México for the treatment of respiratory diseases, against drug-sensitive and drug-resistant strains of Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae type b and Mycobacterium tuberculosis. Forty-eight organic and aqueous extracts were tested against these bacterial strains using a broth microdilution test. No aqueous extracts showed antimicrobial activity, whereas most of the organic extracts presented antimicrobial activity against at least one of the drug-resistant microorganisms tested. Methanol-based extracts from the roots and leaves of Leucophyllum frutescens and ethyl ether extract from the roots of Chrysanctinia mexicana showed the greatest antimicrobial activity against the drug-resistant strain of Mycobacterium tuberculosis; the minimal inhibitory concentration (MIC) were 62.5, 125 and 62.5 microg/mL, respectively; methanol-based extract from the leaves of Cordia boissieri showed the best antimicrobial activity against the drug-resistant strain of Staphylococcus aureus (MIC 250 microg/mL); the hexane-based extract from the fruits of Schinus molle showed considerable antimicrobial activity against the drug-resistant strain of Streptococcus pneumoniae (MIC 62.5 microg/mL). This study supports that selecting plants by ethnobotanical criteria enhances the possibility of finding species with activity against resistant microorganisms.     

Antibacterial potential of Antarctic lichens against human pathogenic Gram-positive bacteria

Extracts from five Antarctic lichens (L3, Stereocaulon alpinum; L5, Ramalina terebrata; L6, Caloplaca sp.; L8, Lecanora sp.; and L17, Caloplaca regalis) were tested for antimicrobial activities against several clinically important microbes by disk diffusion. The minimum inhibitory concentration (MIC) of each extract was determined by a broth dilution method. Extracts from L3, L5, L6 and L8 were active against two Gram(+) strains. B. subtilis was more sensitive to lichen extracts (except L5) than S. aureus. The MIC of lichen extracts against B. subtilis and S. aureus was observed from 36.7 +/- 0.3 to 953.8 +/- 85.8 microg/mL and 68.5 +/- 0.6 to >1000 microg/mL, respectively. Comparisons of MIC values of Antarctic lichen crude extracts to previously published MIC values of some reported lichen metabolites against Gram(+) bacteria indicated that Antarctic lichens might be an enriched source of effective antibacterial agents against clinically relevant Gram(+) species.