Assessment of Antibacterial Activity of Colebrookia oppositifolia against Waterborne Pathogens Isolated from Drinking Water of the Pothwar Region in Pakistan

An attempt was made to control waterborne pathogens by using medicinal plant extracts. One hundred and twenty-six water samples from filtration plants, tube wells, and water supplies were collected and analyzed for total and faecal Coliform bacteria as well as for total viable count. Results showed that waterborne pathogens were numerous and significantly higher than the World Health Organization's recommended guidelines. The methanolic and aqueous extracts of different parts of Colebrookia oppositifolia (Labiateae) were examined for antibacterial activities in vitro by an agar diffusion method. Antibacterial activity of leaves, shoots, and roots of Colebrookia oppositifolia was assessed against Gram positive and Gram negative bacteria that were isolated and identified from water samples by the API 20E method. Extract of roots showed more antibacterial activities against Staph. aureus and B. cereus var. mycoides, Pseudomonas aeruginosa, Klebsiella pneumonia, and Shigella flexneri at 37°C, than extracts from leaves and shoots. The lowest MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) were observed in roots as compared to shoots and leaves. These results suggest that there is an urgent need for improvement in existing water quality treatment. Secondly, the fruit extract can be practical for protection and to avoid risk of contamination by waterborne pathogens and to promote indigenous solutions for disease-control and environmental management.     

Phytochemical Diversity,Classification and Antibacterial Activity of Some Medicinal Plant Species from Tabuk (Saudi Arabia)

The main objectives of this study were to investigate the intra-specific and inter-specific phytochemical diversity and classification of nine important medicinal plant species from Tabuk region (KSA), namely (Pulicaria undulata L., Pulicaria incisa Lam., Artemisia herba-alba Asso., Artemisia monosperma Delile, Artemisia judaica L. and Achillea fragrantissima Forssk. from Asteraceae family, Ducrosia flabellifolia Boiss. from Apiaceae family, Thymus vulgaris L. and Lavandula coronopifolia Poir. from Lamiaceae family); to evaluate the antibacterial potentials of the plant extracts, and to inspect the possible associations between phytochemical diversity and contents of different phytochemical classes with the antibacterial activities of plant extracts. GC/MS technique was used to identify phytochemicals in the plant extracts. The standard disk diffusion technique was used to conduct the antibiotic susceptibility against four pathogenic bacterial species (two Gram positive: Staphylococcus aureus and Bacillus subtilis and two Gram negative species: Pseudomonas aeruginosa and Escherichia coli. A total of 160 different phytochemicals belonging to 30 compound classes were separated and identified. A. fragrantissima had the highest phytochemical diversity and P. incisa had the lowest one. Phytochemical beta diversity was 6.2362. Ethanol outperformed other extraction solvents in terms of antibacterial activity, while Pulicaria undulata and T. vulgaris ranked highest among plants in this regard. Gram positive bacterial species were more sensitive to plant extracts compared to Gram negative species. Phytochemical diversity and antibacterial activity of plant extracts against E. coli and P. aeruginosa were positively correlative, terpenoid and benzene & substituted derivative contents exhibited significant (p<0.05) positive correlations with the antibacterial activity against E. coli, terpenoid contents also showed positive correlation with activity against P. aeruginosa; benzene & derivative showed positive correlation with activity against the rest of bacterial species,     

Broad-spectrum antibacterial and antifungal properties of certain traditionally used Indian medicinal plants

Ethanolic extracts of 22 traditionally used Indian medicinal plants were studied for their antimicrobial activity against seven bacteria (Staphylococcus aureus, Salmonella typhimurium, S. paratyphi, S. typhi, E. coli, Shigella dysenteriae and Pseudomonas aeruginosa) and five filamentous fungi (Aspergillus niger, Alternaria alternata, Fusarium chlamydosporum, Rhizoctonia bataticola and Trichoderma viride) and a yeast Candida albicans of clinical origin. Of these, 16 plant extracts showed varied level of antibacterial activity against one or more test bacteria. Similarly antifungal and anticandidal activity was detected among 17 and 9 plant extracts respectively. Broad-spectrum antimicrobial activity (both antibacterial and antifungal) was detected among crude extracts of Bryophyllum pinnatum (leaves), Caesalpinia bonducella (seeds), Delonix regia (flower), Hedychium spicatum (fruits), Mangifera indica (leaves), Murraya coenigii (leaves) and Syzgium cumini (seeds). Similarly extracts of Cichorium intybus (roots), Ficus religiosa (leaves) and Trigonella foenum-graecum (leaves) demonstrated more antibacterial activity with less antifungal activity. On the other hand Pistacia integerrima (stems) and Rheum emodi (roots) demonstrated more antifungal activity with less antibacterial activity.     

Antibacterial spectrum and cytotoxic activities of serrulatane compounds from the Australian medicinal plant Eremophila neglecta

Aims: To determine the antibacterial spectrum and cytotoxic activities of serrulatane compounds from the Australian plant Eremophila neglecta. Methods and Results: Antimicrobial activities of serrulatane compounds 8,19‐dihydroxyserrulat‐14‐ene ( 1 ) and 8‐hydroxyserrulat‐14‐en‐19‐oic acid ( 2 ) were tested against Gram‐negative and Gram‐positive bacteria including human and veterinary pathogens and some multidrug‐resistant isolates. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of the compounds were determined by broth microdilution assay. Both compounds exhibited antibacterial activity against all Gram‐positive test strains. They showed antimycobacterial activity against isolates of Mycobacterium fortuitum and Mycobacterium chelonae. Of the five Gram‐negative bacteria tested, only Moraxella catarrhalis showed susceptibility to the compounds. Cytotoxic activities were tested in the Vero cell line. Compound 1 showed more activity than 2 in both antibacterial and cytotoxicity assays with cytotoxicity at concentrations similar to the MBC. Conclusions: Serrulatane compounds showed significant activity against medically important bacteria, with 1 exhibiting stronger antibacterial activity. However, they also displayed toxicity to mammalian cells. Significance and Impact of the Study: Serrulatanes are of interest as novel antibacterial compounds for use in biomedical applications; this study reports data obtained with a range of bacterial strains and mammalian cells, essential for assessing the capabilities and limitations of potential applicability of these compounds.     

Screening of antifungal activity of various plant leaves extracts from Indian plants

The present study was designated to evaluate the antifungal activity and to root out the antifungal plant leaf extracts from this Indian folk-flore. The in vitro antifungal assay was performed by agar diffusion test and minimum inhibitory concentration (MIC) for hexane, ethyl acetate, methanol and distilled water plant leaf extracts. Extraction of 17 different plant leaves was carried out in different solvents such as hexane, ethyl acetate, methanol and distilled water. Among them extractive yield of methanol was maximum than the rest of the three solvents. These extracts were screened for their antifungal activity against nine different fungi. Among these ethyl acetate extracts of Adhatoda vasica, Ocimum sanctum and Holoptelea integrifolia exhibited maximum antifungal activity against Alternaria sp., Aspergillus parasi, Aspergillus nidulans, Trichoderma harzianum and Aspergillus flavus with MIC of 80, 40 and 20 ppm against Aspergillus nidulans and Alternaria sp. Ethyl acetate extracts showed promising antifungal activity against Adhatoda vasica, Ocimum sanctum and Holoptelea integrifolia against Aspergillus nidulans, and Alternaria sp. might be applicable as fungicide against fungal plants disease.     

Fungitoxic and Phytotoxic Studies with Essential Oil of Ocimum adscendens

On screening the leaf extracts of some higher plants for their volatile antifungal activity against the test organism Aspergillus flavus, the extract of Ocimum adscendens exhibited the strongest fungitoxicity. The leaves showed maximum, fungitoxicity as compared with other plant parts. The volatile fungitoxic fraction obtained as an essential oil was standardized by various physico-chemical properties. The oil showed its fungicidal nature and broad range of activity at its minimum inhibitory concentration. The oil was thermostable and the toxicity remained unchanged even on autoclaving and on storage for up to 360 days. Moreover, the oil proved more active than some prevalent synthetic fungicides and exhibited no phytotoxic effect onVigna radiata.     

Achillea filipendulina Lam.: Chemical Constituents and Antimicrobial Activities of Essential Oil of Stem,Leaf, and Flower

In this study, we extracted the essential oils of the stem, leaf, and flower of Achillea filipendulina, analyzed them, and studied their antibacterial properties. Of 16, 53, and 35 compounds identified in the stem, leaf, and flowers, respectively, only five are present in all three segments of the plant. The essential oil of the stem was mainly composed of neryl acetate, spathulenol, carvacrol, santolina alcohol, and trans‐caryophyllene oxide. However, the main identified components of leaf were 1,8‐cineole, camphor, ascaridole, trans‐isoascaridole, and piperitone oxide and the main components of the flower oil were ascaridole, trans‐isoascaridole, 1,8‐cineole, p‐cymene, and camphor. The extracted oil from different segments demonstrated varying antibacterial properties against both Gram‐positive and Gram‐negative bacteria, demonstrated by disk, minimum inhibitory concentration, and minimum bactericidal concentration methods. These suggest that the application of all segments of aerial parts of A. filipendulina may have a better therapeutic effect in fighting pathogenic systems.     

Antibacterial activity of herbal extracts against five plant pathogenic bacteria

The present study was designed to evaluate in vitro antibacterial activity of herbal extracts against five plant pathogenic bacteria (viz. Xanthomonas campestris, Xanthomonas axonopodis pv. punicae, Erwinia spp., Pseudomonas syringae and Xanthomonas citri). Herbal extracts of leaves and rinds of Garcinia indica, rhizomes of Curcuma aromatica, roots of Glyccyrrhiza glabra, leaves of Nyctanthes arbor-tristis and seeds of Vernonia anthelmintica were used for screening. Screening was done using agar well diffusion method. Relatively potent extracts were shortlisted from this study and were further studied to find out their minimum bactericidal concentration (MBC). From the studies, it was observed that extracts of C. aromatica, G. indica and G. glabra have shown lowest MBC values among other tested plant extracts. This study indicates the potential of these potent plant extracts in the management of diseases caused by plant pathogenic bacteria.     

Study of antimicrobial activity and root symbionts of Hemionitis arifolia

Antibacterial and antifungal activity of crude extract, alcoholic extract and extracted phenol from various parts of tropical pteridophyta, Hemionitis arifolia were tested by agar diffusion and tube dilution assay. Both the crude and alcoholic extracts of vegetative and reproductive leaves of H. arifolia showed considerable antibacterial activity against Gram negative test strain of Escherichia coli (MTCC-739). Extract from reproductive leaves also showed moderate antibacterial activity against Bacillus subtilis (MTCC-441) (Gram positive test strain) but didn’t show any antifungal activity against Candida albicans (MTCC-7353). Mycorrhizal and other symbiotic association with the root system of H. arifolia was studied and it is revealed that a number of mycorrhizal strains were present in both vegetative and reproductive form. Presence of Dark Septate Endophytic Fungi (DSF) was also detected.     

Phytochemical, antimicrobial, antioxidant and antigenotoxic potentials of Cyperus rotundus extracts

The aqueous, ethyl acetate, methanolic and Total Oligomer Flavonoids (TOF) enriched extracts, obtained from the aerial parts of Cyperus rotundus, were investigated for their contents in phenolic compounds. Antioxidative activity using the NBT/riboflavin assay system, antimicrobial activity against Gram positive and Gram negative bacterial reference strains as well as antigenotoxic activity tested with the SOS chromotest assay were also studied. Significant antibacterial activity against reference strains; Staphylococcus aureus, Enterococcus faecalis, Salmonella enteritidis and Salmonella typhimurium, was detected in the presence of ethyl acetate and TOF enriched extracts. In addition to their antimicrobial activity, the same extracts showed a significant ability to inhibit nitroblue tetrazolium reduction by the superoxide radical in a non enzymatic O₂^.− generating system, and were also able to reduce significantly the genotoxicity induced by nifuroxazide and Aflatoxin B1. The antioxidant, antimicrobial and antigenotoxic activities exhibited by C. rotundus depend on the chemical composition of the tested extracts.     

Copper Oxide Nanomaterials Derived from Zanthoxylum armatum DC. and Berberis lycium Royle Plant Species: Characterization,Assessment of Free Radical Scavenging and Antibacterial Activity

Copper oxide nanomaterials were synthesized by a facile sustainable biological method using two plant species (Zanthoxylum armatum DC. and Berberis lycium Royle ). The formation of materials was confirmed by FT‐IR, ATR, UV‐visible, XRD, TEM, SEM, EDX, TGA and PL. The antibacterial activity was evaluated by agar well diffusion method to ascertain the efficacy of plant species extract and extract derived copper oxide nanomaterials against six Gram‐positive bacteria namely Staphylococcus aureus, Streptococcus mutans, Streptococcus pyogenes, Corynebacterium diphtheriae, Corynebacterium xerosis, Bacillus cereus and four Gram‐negative bacteria such as Klebsiella pneumonia, Escherichia coli, Pseudomonas aeruginosa and Proteus vulgaris against the standard drug, Ciprofloxacin for Gram‐positive and Gentamicin for Gram‐negative bacteria, respectively. In both cases, copper oxide nanomaterials were found to be sensitive in all the bacterial species. Sensitivity of copper oxide nanomaterials shows an be higher as compared to plant species extract against different bacteria. Scavenging activity of plant extracts along with nanomaterials have been accessed using previously reported protocols employing ascorbic acid as standard. Scavenging activity of copper oxide nanomaterials shows an increase with increase in concentration. The biological activity (bactericidal and scavenging efficiency) of plant derived copper oxide nanomaterials revealed that these materials can be used as potent antimicrobial agent and DPPH scavengers in industrial as well as pharmacological fields.     

Volatile Chemical Composition,Antibacterial and Antifungal Activities of Extracts from Different Parts of Globba schomburgkii Hook.f.

Globba schomburgkii Hook.f. is an ornamental plant that has recently found increasing demand as cut flowers, hence generating a significant number of by‐products from different parts of the plant. To investigate the further applications of these by‐products, twelve crude extracts from rhizomes, stalks, leaves, and flowers were prepared by serial exhaustive extraction. The volatile composition of these extracts was analyzed by GC/MS; a total of 89 compounds were identified, most of which were sesquiterpenes as well as some labdane‐type diterpenes. The antimicrobial activities of these extracts were evaluated, revealing a correlation between the terpenoid content and antibacterial activities. Notably, the dichloromethane extracts of rhizomes and flowers, which contained the highest amount of terpenoids (e. g., α‐gurjunene, guaia‐9,11‐diene, γ‐bicyclohomofarnesal, β‐caryophyllene, and caryophyllene oxide), displayed the most prominent antibacterial activities. This work demonstrates the potential use of the crude extracts from G. schomburgkii as natural antibacterial ingredients for pharmaceutical and other applications.     

侧柏乙醇提取物对21种植物病原真菌的抑菌活性

采用菌丝生长速率法测定了侧柏(Platycladus orientalis)叶、小枝、球果和种子4个不同部位乙醇提取物对21种植物病原真菌的抑菌活性。结果显示:(1)在供试浓度为50g/L(相当于干样)时,侧柏各部位乙醇提取物对4种供试植物病原真菌均具有较好抑制作用,其中侧柏叶提取物的抑菌效果最好,对供试葡萄白腐病菌(Conio-thyrium diplodiella)、葡萄黑痘病菌(Elsinoe ampelina)、番茄绵腐病菌(Phytophthora melongenae)和青霉病菌(Penicilliu mexpansum)的EC50分别为:5.424、3.186、8.913和19.000g/L。(2)侧柏叶乙醇提取物的石油醚萃取物和乙酸乙酯萃取物抑菌活性均较好,在供试浓度为0.5g/L时,石油醚萃取物对苹果腐烂病菌(Valsa mali)和葡萄黑痘病菌(E.ampelina)的抑菌率分别为80.35%和60.23%;乙酸乙酯萃取物对以上2种植物病原菌的抑菌率分别为81.88%和64.06%。结果表明:侧柏叶、小枝、球果和种子乙醇提取物均具有一定抑菌活性,叶乙醇提取物的活性最好,活性成分主要集中在石油醚萃取物和乙酸乙酯萃取物中。     

Interference of Seasonal Variation on the Antimicrobial and Cytotoxic Activities of the Essential Oils from the Leaves of Iryanthera polyneura in the Amazon Rain Forest

The essential oils (EOs) obtained from the leaves of Iryanthera polyneura Ducke trees was chemically Assessed and tested for the ability of inhibiting the growth of Candida albicans, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus mutans and S. sanguinis. The oil was also tested against breast (MCF‐7) and prostate (PC‐3) cancer cell lines. Minimum bactericidal concentrations (MBCs) and 50 % inhibition concentrations (IC₅₀) values were obtained. EOs were active against Gram‐positive bacteria. Spathulenol, α‐cadinol and τ‐muurolol were major components of EOs. The oils showed a higher cytotoxicity against PC‐3 than MCF‐7 cells, although the oils were active against both cell types. Oils obtained from leaves collected in the dry season were more active against E. faecalis, S. aureus and PC‐3, while the oils obtained from leaves collected in the rainy season were more active against S. mutans, S. sanguinis and MCF‐7. The antibacterial and cytotoxic activities of the essential oils from the leaves of I. polyneura are related to the seasonal climate variation and are influenced by compounds that are minor components of the oils.     

Influence of plant polyphenols and medicinal plant extracts on antibiotic susceptibility of Escherichia coli

Aims: To investigate the influence of polyphenols and plant extracts on the susceptibility of Escherichia coli to antibiotics. Methods and Results: Susceptibility of E. coli to antibiotics in the presence of extracts and polyphenols was estimated by the determination of the minimum inhibitory concentrations (MICs). To study gene expression, we used strains of E. coli carrying fusions between promoters of genes katG, sodA, iucC and structural β‐galactosidase gene. Treatment with polyphenols and some plant extracts significantly decreased the antibacterial effects of antibiotics, to a larger extent, ciprofloxacin. The most remarkable protective effect was observed for the extracts of Chamerion (Epilobium) angustifolium, Filipendula vulgaris, Tanacetum vulgare and Serratula coronata. These extracts increased the MICs of ciprofloxacin by four and more times. In case of kanamycin, extracts of Artemisia austriaca and Artemisia pontica increased MICs by four and eight times, respectively. Polyphenol quercetin also caused protective effect against ciprofloxacin, increasing the MIC by four times. A positive correlation was found between protective effects of polyphenols and extracts and their antioxidant activity. Conclusion: Medicinal plant extracts and polyphenols may protect cells of E. coli against antibiotic toxicity. Significance and Impact of the Study: The results of this study may be used to enhance the efficiency of antibacterial therapies.     

Antibacterial activity of guava,moringa, camphor bush and pelargonium extracts against bacterial wilt (Ralstonia pseudosolanacearum sp. nov.) of potato

Bacterial wilt (Ralstonia pseudosolanacearum sp. nov.) is a major disease devastating global potato production. Proposed management options are mostly expensive and ineffective. This has necessitated efforts to develop cheaper and eco-friendly management options such as use of botanicals. Antibacterial activity of ethanol and acetone plant extracts from guava (Psidium guajava), drumstick (Moringa oleifera), camphor bush (Tarchonanthus camphoratus) and pelargonium (Pelargonium zonale) against R. pseudosolanacearum sp. nov. was evaluated in-vitro at a concentration of 100 mg/mL of 1 % Dimethlysulfoxide (DMSO) using disk diffusion technique. The R. pseudosolanacearum sp. nov was isolated from infected haulms collected from potato growing field at the University of Nairobi. The most effective extracts were subjected to further screening at different concentrations to determine their minimum inhibitory concentrations (MICs). All the four plant extracts showed varied antibacterial efficacy. P. zonale leaves extract was the most effective with growth inhibition zone of 18.73 mm and 18.60 mm for ethanol and acetone solvents respectively. The average of growth inhibition zones for each plant extract was not significantly different at p ≤ 0.05 among extraction solvents. The minimum inhibitory concentration (MIC) results showed that antibacterial activity of P. zonale and P. guajava leaf started at 6.25 mg/mL with growth inhibition zones of 7.67 and 8.0 mm for ethanol and acetone solvents respectively. P. zonale and P. guajava leaf extracts exhibited significantly higher antibacterial activity at p ≤ 0.05 compared to other extracts. Thus, further research should be conducted to assess their antibacterial potency against R. pseudosolanacearum sp. nov. both in-vivo and under field condition.     

Identification of vibriocidal compounds from medicinal plants using chromatographic fingerprinting

The aim of the present study was to investigate the vibriocidal activity of bark of Syzygium cumini, leaves of Lawsonia inermis, fruits of Terminalia bellerica and identify the bioactive compounds. The vibriocidal activity of plant extracts was determined in aqueous and organic solvents, and the minimum inhibitory concentration (MIC) against Vibrio spp. using the disk diffusion method was established. The chemical constituents of the plant extracts were analysed by thin layer chromatography (TLC), the vibriocidal compounds were determined by TLC-bioautography and were further confirmed by high performance liquid chromatography (HPLC). Significant inhibitory activity was observed with ethanol extract of plants against the test bacteria while less antibacterial activity was observed in acetone, methanol and aqueous extracts. The MIC of the plant extracts ranged between 2.5 and 20 mg/ml. The TLC, TLC-bioautography and HPLC analysis showed that gallic acid and tannin present in ethanol extracts of S. cumini, tannin present in L. inermis and gallic acid present in T. bellerica may be responsible for the vibriocidal activity. S. cumini, L. inermis and T. bellerica can be used for the treatment of gastroenteritis, diarrhoea and cholera diseases after detailed investigations. We also conclude that the plants rich in gallic acid and tannin can be used as an alternative to search for new vibriocidal drugs.     

Antifungal activity of herbal extracts against plant pathogenic fungi

The present study was designed to evaluate in vitro antifungal activity of herbal extracts against three plant pathogenic fungi (viz. Rhizopus stolonifer, Botrytis cinerea and Colletotrichum coccodes). Extracts of leaves and rinds of Garcinia indica, rhizomes of Curcuma aromatica, roots of Glycyrrhiza gahliae, leaves of Nyctanthes arbour-tristis and seeds of Vernonia anthelmintica were used for screening. Screening was done using poisoned food technique. Relatively potent extracts were shortlisted from this study and were further assayed to find out their minimum fungicidal concentration (MFC). From the above studies, it was observed that ethyl acetate extract of rhizomes of C. aromatica and unripe fruit rinds of G. indica have shown the lowest MFC values amongst the other tested plant extracts. This study indicates that the potential of these plant extracts in the management of diseases caused by plant pathogenic fungi.     

In vitro evaluation of Datura innoxia (thorn-apple) for potential antibacterial activity

Various parts of Datura innoxia were examined for potential antibacterial activity by preparing their crude aqueous and organic extracts against Gram-negative bacteria (Escherichia coli and Salmonella typhi) and Gram-positive bacteria (Bacillus cereus, Bacillus subtilis and Staphylococcus aureus). The results of agar well diffusion assay indicated that the pattern of inhibition depends largely upon the plant part, solvent used for extraction and the organism tested. Extracts prepared from leaves were shown to have better efficacy than stem and root extracts. Organic extracts provided potent antibacterial activity as compared to aqueous extracts. Among all the extracts, methanolic extract was found most active against almost all the bacterial species tested. Gram-positive bacteria were found most sensitive as compared to Gram-negative bacteria. Staphylococcus aureus was signifi cantly inhibited by almost all the extracts even at very low MIC followed by other Gram-positives. For Escherichia coli (a Gram-negative bacterium), the end point was not reached for ethyl acetate extract while it was very high for other extracts. The study promises an interesting future for designing a potentially active antibacterial agent from Datura innoxia.     

Antimicrobial effect of different herbal plant extracts against different microbial population

This study evaluates the antimicrobial effects of ethanolic extract of five herbal plants; Guava (Psidium guajava), Sage (Salvia officinalis), Rhamnus (Ziziphusspina Christi), Mulberry (Morusalba L.), and Olive (Oleaeuropaea L) leaves against several microbial population representing Gram positive, Gram negative and Mollicutes; S. aureus, E. coli, Pasteurella multocida, B. cereus, Salmonella Enteritidis and M. gallisepticum using standard agar disc diffusion technique and minimal inhibitory concentration (MIC). Different extracts reveal variable results against the microorganism under study. All extracts have no antibacterial potency for Mycoplasma gallisepticum except Psidium guajava. The results of minimal inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) of the extracts against the six bacteria ranged from 625 to 5000 μg/ml. The used herbal extract could inhibit the selected microorganism under study with variable minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC).