Antimicrobial Effects of Essential Oils onStreptococcus pneumoniae

Antibacterial Effect of Eight Essential Oils against Bacteria Implicated in Bovine Mastitis and Characterization of Primary Action Mode of Thymus capitatus Essential Oil

During the current investigation, eight essential oils (EOs) were tested for their antimicrobial activity against six species, belonging to the genus of staphylococcus, multi-resistant to antibiotics (S. epidermidis, S. cohni, S. wareneri, S. scuiri, S. chromogenes, S. pasteuri), three methicillin-resistant Staphylococcus aureus strains (MRSA) and two strains of Escherichia coli, producing extended-spectrum β-lactamase (ESBL) responsible for bovine mastitis. Our results indicated that the antimicrobial activities of eight EOs varied significantly among the types of EOs and bacterial species. Thymus capitatus and Trachyspermum ammi EOs display important antibacterial activity against all tested strains, with the inhibition zone diameters situated between 20 and 45 mm, while EOs of Artemisia absinthium, Eucalyptus globulus, Eucalyptus camaldulensis, Myrtus communis and Mentha pulegium exerted an intermediate activity. For Cymbopogon citratus, this effect depends on bacteria species. In fact, an important effect was observed against S. warneri, S. epidermidis, S. cohenii, S. pasteuri and MRSA (EC 39+) strains. In addition, the important lytic effect was observed against MRSA strains, showing that Gram-positive bacteria were more sensitive to T. capitatus EO than Gram-negative ones. Concerning the characterization of the mode action of T. capitatus, experiments of kill-time, bacteriolytic, loss of salt tolerance and loss of cytoplasmic material showed that the used EO was able to destroy cell walls and membranes followed by the loss of vital intracellular materials. In addition, it inhibits the normal synthesis of DNA, causing the bacterial death of E. coli and MRSA strains. This study shows the potential of using of EOs, particularly T. capitaus, to inhibit the growth of Gram-positive and Gram-negative bacteria multi-resistant to antibiotics causing bovine mastitis.

In Vitro Antioxidant, Antibacterial and Mechanisms of Action of Ethanolic Extracts of Five Tunisian Plants against Bacteria

Pistacia lentiscus, Rosmarinus officinalis, Erica multiflora, Calicotome villosa, and Phillyrea latifolia were considered important medicinal herbs and were used to treat various ailments. The present study was designed to evaluate the antioxidant and antimicrobial activities of ethanolic extracts (EEs). P. lentiscus and R. officinalis were the richest species in phenolic compounds. Similarly, both species showed the highest values of flavonoids. While the EEs of P. lentiscus, E. multiflora, and C. villosa had higher amounts of tannins. These phenolic compounds were evaluated by two different tests, namely diphenyl picrylhydrazyl (DPPH) and ferric iron-reducing power (FRAP). The IC50 values were found to be significant (p < 0.05) for P. lentiscus and E. multiflora. Similarly, both plants showed the highest ferric-reducing antioxidant power (FRAP). This study has been conducted to evaluate the antibacterial potential of EEs against selected bacteria—Gram-positive bacteria (Staphylococcus aureus ATCC 29213, Listeria monocytogenes ATCC 7644) and Gram-negative bacteria (Escherichia coli ATCC 8739, Salmonella typhimurium NCTC 6017)—and determine their modes of action. The ethanolic extracts inhibited bacterial growth by producing concentration-dependent zones of inhibition. Treatment with these extracts at their minimum inhibitory concentrations (MICs) showed a significant reduction (p < 0.05) in the viability of bacteria. The extracts did not induce total lysis. Bacteria organisms treated with EEs at MICs showed a significant (p < 0.05) loss of tolerance to NaCl (5%). Our results highlighted the use of plant extracts as natural antibacterials that can be safely used in health care and led to the understanding of the antibacterial mechanism of plant extracts.

Characterization of Primary Action Mode of Eight Essential Oils and Evaluation of Their Antibacterial Effect against Extended-Spectrum β-Lactamase (ESBL)-Producing Escherichia coli Inoculated in Turkey Meat

The current study aims to evaluate the antimicrobial activity of eight essential oils (EOs) against multidrug-resistant Escherichia coli strains, producing extended-spectrum β-lactamase (ESBL) enzymes and isolated from foods. Disc-diffusion assay showed that the inhibition diameters generated by EOs varied significantly among the tested EOs and strains. In fact, EOs extracted from Thymus capitaus, Eucalyptus camaldulensis, Trachyspermum ammi and Mentha pulegium exerted an important antimicrobial effect against tested strains, with the diameters of inhibition zones varied between 20 and 27 mm. Moreover, minimal inhibition and bactericidal concentration (MIC and MBC) values demonstrated that T. capitatus EOs generate the most important inhibitory effect against E. coli strains, with MIC values ranging from 0.02 to 0.78%. Concerning the mode of action of T. capitatus EO, the obtained data showed that treatment with this EO at its MIC reduced the viability of E. coli strains, their tolerance to NaCl and promoted the loss of 260-nm-absorbing material. In addition, in the presence of T. capitatus EO, cells became disproportionately sensitive to subsequent autolysis. Moreover, the inhibitory effect of T. capitatus was evaluated against two E. coli strains, experimentally inoculated (10⁵ CFU/g) in minced turkey meat, in the presence of two different concentrations of EO (MIC and 2 × MIC), and stored for 15 days. In both samples, EO exerted a bacteriostatic effect in the presence of concentrations equal to MIC. Interestingly, at 2 × CMI concentration, the bactericidal activity was pronounced after 15 days of storage. Our results highlighted that the use of essential oils, specially of T. capitatus, to inhibit or prevent the growth of extended-spectrum β-lactamase (ESBL)-producing E. coli in food, may be a promising alternative to chemicals.

Antimicrobial and Antioxidant Secondary Metabolites from Trifolium baccarinii Chiov. (Fabaceae) and Their Mechanisms of Antibacterial Action

The treatment of infectious diseases with antimicrobial agents continues to present problems in modern-day medicine with many studies showing significant increase in the incidence of bacterial resistance to several antibiotics. The screening of antimicrobial activity of plant extracts and natural products has shown that medicinal plants are made up of a potential source of new anti-infective agents. The aim of this study was to evaluate the antimicrobial and antioxidant activities of extracts and compounds from the whole plant Trifolium baccarinii Chiov. and to determine their modes of antibacterial action. The plant extracts were prepared by maceration in organic solvents. The antimicrobial activities were evaluated using the broth microdilution method. The antioxidant activity was evaluated using the 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) assays. The mechanisms of antibacterial action were determined by lysis, salt tolerance assays, and antioxidant enzyme activities. The cytotoxic effect on the erythrocytes was determined by a spectrophotometric method. Biochanin A, formononetin, luteolin, luteolin-4'-O-β-D-glucopyranoside, 4,7,2'-trihydroxy-4'-methoxyisoflavanol, sissotrin, 1-methyl-β-D-glucopyranoside, ononin, D-mannitol, and 3-O-β-D-glucuronopyranosylsoyasapogenol B were isolated from Trifolium baccarinii. The MeOH, EtOAc, and n-BuOH extracts as well as biochanin A, formononetin, luteolin, luteolin-4'-O-β-D-glucopyranoside, 4,7,2'-trihydroxy-4'-methoxyisoflavanol, and sissotrin from Trifolium baccarinii displayed the highest antimicrobial and antioxidant activities. The MeOH extract and 4,7,2'-trihydroxy-4'-methoxyisoflavanol exhibited antibacterial activity through the bacteriolytic effect and reduction of the antioxidant defenses in the bacterial cells. The present study portrays Trifolium baccarinii as a potential natural source of antibacterial, antifungal, and antioxidant agents.

Evaluation of Antimicrobial Potential and Comparison of HPLC Composition, Secondary Metabolites Count, and Antioxidant Activity of Mentha rotundifolia and Mentha pulegium Extracts

In the present study, the relationship between the phenolic counts, chemical composition, and biological activities of two Mentha species (Mentha rotundifolia (MR) and Mentha pulegium (MP)) was analyzed. The characterization of the action mode against pathogenic bacteria and the inhibition of spore germination of two fungal species using prepared methanolic extracts were studied here for the first time. The obtained data highlighted the presence of positive correlation between the secondary metabolites contents and the biological activities of the investigated extracts. In fact, HPLC analysis showed that the major components in both the extracts were eriocitrin and rosmarinic acid (25 and 20 mg/ml and 12 and 8 mg/ml in methanolic extracts of MR and MP, respectively). Moreover, the MR extract was rich in polyphenols and presents the highest antioxidant activity than MP ones. In addition, both extracts possess an antimicrobial activity against four Gram-positive and five Gram-negative bacteria and one yeast species (Candida albicans) and were able to inhibit the spore germination of two fungi species (Aspergillus niger and Aspergillus flavus). But, the significant activity was observed in the presence of MR methanolic extract. The effect of time on cell integrity of E. coli and L. monocytogenes determined by time-kill and bacteriolysis assays showed that the MR extract had a rapid bacteriolytic effect compared to the MP extract, and their capacities were significant against Gram-negative bacteria than positive ones. Based on the obtained data, it can be concluded that Saudi Mentha species have high pharmacological and industrial importance and they can be used in preparation of food or drugs.

HPLC-Analysis, Biological Activities and Characterization of Action Mode of Saudi Marrubium vulgare against Foodborne Diseases Bacteria

The present study aims to evaluate the chemical composition, metabolites secondary and pharmacology activities of methanolic extract of Marrubium vulgare collected from King Saudi Arabia. Moreover, the primary mode of action of the tested extract was studied here for the first time against E. coli and L. monocytogenes. HPLC analysis shows that the major components in the tested extract are luteolin-7-O-d-glucoside, ferulic acid and premarrubiin. Obtained data demonstrated that the investigated extract was richer in phenol (26.8 ± 0.01 mg/GAE g) than in flavonoids (0.61 ± 0.05 mg EC/mL). In addition, the methanolic extract showed an important antioxidant capacity against the DPPH (IC₅₀ = 35 ± 0.01 µg/mL) and ABTS (IC₅₀ = 25 ± 0.2 µg/mL) radical scavenging and a strong inhibition of acetylcholinesterase enzyme with an IC₅₀ value corresponding to 0.4 mg/mL. The antibacterial activity demonstrated that the evaluated extract had significant activity against both Gram-positive and Gram-negative bacteria. The effect of time on cell integrity on E. coli and L. monocytogenes determined by time-kill and bacteriolysis tests showed that the M. vulgare extract reduced the viability of both strains after 8 and 10 h and had a bacteriolytic effect against two different categories of bacteria, Gram-positive and negative, which are not of the same potency. Based on obtained data, it can be concluded that Saudi M. vulgare has a high pharmacological importance and can be used in preparation of food or drugs.

Thai herbal formulation 'Ya-Pit-Samut-Noi': Its antibacterial activities, effects on bacterial virulence factors and in vivo acute toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

A Thai herbal formulation 'Ya-Pit-Samut-Noi' containing Nigella sativa (seed), Piper retrofractum (fruit), Punica granatum (pericarp), and Quercus infectoria (nutgall) has long been traditionally used to treat diarrhea or bloody mucous diarrhea. Scientific information is very important to support its therapeutic effects and traditional drug development.

AIM OF THE STUDY

This study aimed to evaluate the antibacterial activities of Ya-Pit-Samut-Noi against diarrhea-causing bacteria and determine its effects on bacterial virulence factors and in vivo acute toxicity.

MATERIALS AND METHODS

Ethanol and water extracts of Ya-Pit-Samut-Noi and its plant components were prepared. The agar diffusion method was used for preliminary screening of antibacterial activity of the extracts against diarrhea-causing bacteria including Staphylococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were assessed using broth microdilution method. The effects on bactericidal activity, bacterial cell wall, and cell membrane were examined by time-kill, lysis, and leakage assays, respectively. The effects on bacterial virulence factors including quorum-sensing system, biofilm production, and swarming motility were determined. Phytochemical screening was carried out to identify the group of chemical compounds present in the formulation extracts. Acute toxicity study was conducted by a single oral dose of 2000 mg/kg body weight in Wistar albino rats.

RESULTS

Ethanol and water extracts of Ya-Pit-Samut-Noi and Quercus infectoria demonstrated antibacterial efficacy against all bacterial strains as revealed by zones of inhibition ranging from 7.0 to 24.5 mm. The ethanol and water extracts of Ya-Pit-Samut-Noi and Quercus infectoria produced strong bacteriostatic activity against V. parahaemolyticus (n = 11) with an MIC range of 7.81-250 μg/ml. Only the ethanol extract of Ya-Pit-Samut-Noi produced MBC values less than or equal to 1000 μg/ml against all V. parahaemolyticus. Based on time-kill study, no surviving V. parahaemolyticus (ATCC 17802 and 5268) cells were detected within 6-12 h after treatment with the ethanol extract of Ya-Pit-Samut-Noi at MBC-4MBC concentrations. Vibrioparahaemolyticus ATCC 17802 cells treated with the ethanol extract of Ya-Pit-Samut-Noi demonstrated no lysis or leakage through the bacterial membrane was not observed. At low concentrations (0.125-0.25 μg/ml) the ethanol extract of Ya-Pit-Samut-Noi inhibited violacein production by Chromobacterium violaceum DMST 21761 without affecting the bacterial growth. The ethanol (31.25-62.5 μg/ml) and water (31.25-250 μg/ml) extracts of Ya-Pit-Samut-Noi inhibited biofilm production by S. aureus. The ethanol and water extracts of Ya-Pit-Samut-Noi at 1000 μg/ml reduced the swarming motility of Escherichia coli O157: H7 by 74.98% and 52.65%, respectively. Tannins and terpenoids were detected in both the ethanol and water extracts. Flavonoids were present only in the ethanol extract. Alkaloids and antraquinones were not noticed in either extract. In the acute toxicity study, there were no significant changes in hematological and biochemical parameters nor were adverse effects on mortality, general behaviors, body weight, or organ weights detected.

CONCLUSIONS

The scientific evidence from this study supported the therapeutic effects and safety of the traditional Thai herbal formulation 'Ya-Pit-Samut-Noi' which has been used as an alternative treatment for gastrointestinal infections in Thailand.

Antibacterial and Cytotoxic Activity of Nepeta Cataria L., N. Cataria Var. Citriodora (Beck.) Balb. and Melissa Officinalis L. Essential Oils

The aim of the present study was to investigate the susceptibility of bacteria that play a role in respiratory tract and skin infections to the essential oils of catnip (Nepeta cataria), lemon catnip (N. cataria var. citriodora) and lemon balm (Melissa officinalis) with regard to their chemical composition. In addition, we wanted to assess whether antibiotic-resistant and -sensitive strains differ in their susceptibility to the oils and if there are cross resistances between standard antibiotics and essential oils. To evaluate the safety of topical application, cytotoxicity of the oils was studied in human keratinocyte and bronchial epithelial cell lines and irritation threshold concentrations were determined in ovo using the HET-CAM-test. The composition of the essential oils was analyzed by GC and GC-MS. Their MICs and MBCs were determined by a broth microdilution method against both reference strains from culture collections and clinical isolates with different susceptibility to standard antibiotics. Cytotoxicity was assessed by the MTT assay. Except for P. aeruginosa (MIC ≥2%), all reference strains tested were susceptible to catnip and lemon balm oils with MIC values ranging from 0.016 % to 0.25% (v/v). The clinical isolates were as susceptible to the oils (± 1 serial dilution) as the corresponding reference strains, regardless of their origin and resistance to standard antibiotics. The oils were cytotoxic to both keratinocytes and bronchial epithelial cells at CC50 values from 0.0012% to 0.015% (v/v). Lemon balm oil, whose main components were monoterpene aldehydes, exhibited the highest antibacterial and cytotoxic activity, followed by lemon catnip oil, which contained mainly monoterpene alcohols, and catnip oil, which was characterized by nepetalactones. Our results provide a rationale for the use of catnip, lemon catnip and lemon balm oils in the complementary topical treatment of respiratory tract infections, as the oils show a high antibacterial activity against respiratory tract pathogens, including clinical isolates with reduced susceptibility to standard antibiotics. However, cytotoxicity must be considered in topical therapy.

Antibacterial Activity and Irritation Potential of Selected Essential Oil Components – Structure-Activity Relationship

A selection of structurally diverse components of essential oils was subjected to an antibacterial screening against the Gram-positive bacteria Staphylococcus aureus and Streptococcus pneumoniae as well as the Gram-negative bacteria Escherichia coli and Haemophilus influenzae using a broth microdilution method. In addition, the irritation potential of these substances to mucous membranes was evaluated by a modified HET-CAM (Hen's Egg Test-Chorioallantoic Membrane) assay. Minimum inhibitory concentrations (MIC) and irritation threshold concentrations (ITC) were compared in order to identify substances with a low mucous membrane irritation potential at the antibacterially effective concentration. Regarding the antibacterial activity, the most active substances were cinnamaldehyde, phenols, monoterpene alcohols and aldehydes. Oxygenated monoterpenes and phenylpropanoids without either alcohol or aldehyde function (ethers, ketones) showed moderate activity. Mono- and sesquiterpene hydrocarbons, as well as sesquiterpene alcohols, were more or less inactive against most of the bacteria tested, with the exception of Streptococcus pneumoniae whose growth was inhibited by sesquiterpenes at exceptionally low concentrations. In most cases, the irritation potential of the test compounds could also be traced back to their structural features. 2-Phenylethanol, monoterpene alcohols, phenols and aromatic aldehydes had the lowest ITC-values, followed by monoterpene aldehydes, ketones and ethers. In contrast, monoterpene hydrocarbons caused irritation only at higher doses. Of special interest was the fact that all the sesquiterpenes tested were not irritant even when applied undiluted to the chorioallantoic membrane (CAM).

Natural products show diverse mechanisms of action against Clostridium difficile

AIMS

To investigate the mechanisms of action of natural products with bactericidal (cinnamon root powder, peppermint oil, trans-cinnamaldehyde, menthol and zingerone) or bacteriostatic (fresh garlic bulb extract, garlic clove powder, Leptospermum honey and allicin) activity against two Clostridium difficile strains.

METHODS AND RESULTS

Bactericidal products significantly reduced intracellular ATP after 1 h (P ≤ 0·01), quantified using the BacTiter-Glo reagent, and damaged the cell membrane, shown by the leakage of both 260-nm-absorbing materials and protein, and the uptake of propidium iodide. Bacteriolysis was not observed, determined by measuring optical density of treated cell suspensions at 620-nm. The effect of three bacteriostatic products on protein synthesis was quantified using an Escherichia coli S30 extract system, with Leptospermum honey (16% w/v) showing significant inhibition (P < 0·01). Lastly, no products showed elevated minimum inhibitory concentrations against antimicrobial-resistant C. difficile, determined by broth microdilution.

CONCLUSIONS

Cytoplasmic membrane damage was identified as a mechanism of action that may contribute to the activity of several natural products against C. difficile.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study describes the possible mechanisms of action of natural products against C. difficile, yet the efficacy in vivo to be determined.

Lupinifolin from Albizia myriophylla wood: A study on its antibacterial mechanisms against cariogenic Streptococcus mutans

OBJECTIVE

To determine the anti-Streptococcus mutans mechanisms of action of lupinifolin from Albizia myriophylla Benth. (Fabaceae) wood and provide scientific evidence to support the traditional use of the plant against dental caries.

METHODS

The minimum inhibitory concentration (MIC) was evaluated using the broth micro-dilution method. The effects of lupinifolin on bactericidal activity, bacterial cell walls, and membranes were investigated by time-kill, lysis, and leakage assays, respectively. Electron microscopy was utilized to observe any cell morphological changes caused by the compound. Localization of lupinifolin in S. mutans was detected using the thin layer chromatography technique.

RESULTS

The MIC range of lupinifolin against S. mutans (n=6) was 2-4 μg/ml. This compound displayed bactericidal effects on S. mutans ATCC 25175 by 90-99.9% killing at 4MIC-16MIC after 8-24 hours. Lupinifolin-treated cells demonstrated no lysis. However, significant cytoplasmic leakage through the bacterial membrane was observed after treatment with lupinifolin at 4MIC-16MIC. As revealed by ultrastructural analysis, lupinifolin produced some changes in bacterial cell walls and membranes. Moreover, the compound was observed in the cytoplasmic fraction of the lupinifolin-treated cells. These results suggest that lupinifolin can enter the cell of bacteria but does not accumulate in the cell envelope and subsequently disrupts the integrity of the cytoplasmic membrane, leading to cell death.

CONCLUSION

The scientific evidence from this study offers valuable insights into the potential role of lupinifolin in pharmaceutical and antibiotic applications and supports the therapeutic effects of A. myriophylla, which has traditionally been used as an alternative treatment for dental caries.

Anti-Listerial Activity of Four Seaweed Essential Oils Against Listeria monocytogenes

Background

Listeria monocytogenes is one of the most virulent types of bacteria and causes severe foodborne illness, such as listeriosis. Because this pathogen has become resistant to sanitizers and other disinfectants that are used to clean utensils and surfaces during food processing, it poses a serious threat to the food industry.

Objectives

The study was conducted to determine the anti-listerial potential of essential oils extracted from four edible seaweeds against L. monocytogenes.

Materials and Methods

Essential oil was extracted from four edible seaweeds (Enteromorpha linza, Undaria pinnatifida, Laminaria japonica, and Porphyra tenera) against L. monocytogenes using the microwave hydrodistillation method. The anti-listerial activity of the essential oil was determined using the standard disc diffusion method.

Results

Among the four essential oils, E. linza (ELEO) was most effective against all three strains of L. monocytogenes (11.3 - 16.0 mm). The other three essential oils were only effective against two strains, L. monocytogenes ATCC 19115 (10.0 - 10.5 mm) and L. monocytogenes ATCC 7644 (11.0 - 15.0 mm). The minimum inhibitory concentration and the minimum bactericidal concentration of all four essential oils varied from 12.5 - 25.0 mg/mL. Further, the mode of action of ELEO against L. monocytogenes was investigated by examining its effect on cell viability, the release of 260-nm absorbing materials, the number of K+ ions, the relative electrical conductivity, and the salt tolerance capacity. The results indicated that the essential oils exhibited strong anti-listerial activity against multiple strains of L. monocytogenes. It displayed potential inhibitory effects on the viability of bacterial cells and loss of integrity as indicated by an increase in the relative electrical conductivity, leakage of K+ ions and other 260-nm absorbing materials, and a loss of the salt tolerance capacity.

Conclusions

The results presented herein provided insight into a possible explanation for the modes of action of essential oils on L. monocytogenes. The outcome of the present study may aid the food industry in locating the most promising potential anti-listerial agents from edible seaweed sources to control L. monocytogenes and also in facilitating their application in food processing and preservation techniques in a nontoxic and environmental friendly manner.

Volatile oils: Potential agents for the treatment of respiratory infections

Due to presence of secondary bioactive metabolites, natural compounds are considered a major source of new active molecules that can be developed as new drugs. Infectious diseases, and mainly the common respiratory infections, are major challenges to the current chemotherapy systems and, therefore, there is a requirement to find new compounds with therapeutic potential. The volatile natural compounds and essential oils are the main treasure agents in the natural compounds with antibiotic potential. The present chapter reviews natural traditional remedies used in the treatment of respiratory infections with the emphasis on antibacterial, antiviral, and antiinflammation activities of the volatile natural compounds (essential oils, etc.), and provides a brief view in some of structural activity relationships between antibacterial potencies and chemical structures of the essential oil’s constituents.

Essential oils, a new horizon in combating bacterial antibiotic resistance

For many years, the battle between humans and the multitudes of infection and disease causing pathogens continues. Emerging at the battlefield as some of the most significant challenges to human health are bacterial resistance and its rapid rise. These have become a major concern in global public health invigorating the need for new antimicrobial compounds. A rational approach to deal with antibiotic resistance problems requires detailed knowledge of the different biological and non-biological factors that affect the rate and extent of resistance development. Combination therapy combining conventional antibiotics and essential oils is currently blooming and represents a potential area for future investigations. This new generation of phytopharmaceuticals may shed light on the development of new pharmacological regimes in combating antibiotic resistance. This review consolidated and described the observed synergistic outcome between essential oils and antibiotics, and highlighted the possibilities of essential oils as the potential resistance modifying agent.

In Vitro Antibacterial and Antibiotic Resistance Modifying Effect of Bioactive Plant Extracts on Methicillin-Resistant Staphylococcus epidermidis

The crude extracts of plants from Asteraceae and Lamiaceae family and essential oils from Salvia officinalis and Salvia sclarea were studied for their antibacterial as well as antibiotic resistance modifying activity. Using disc diffusion and broth microdilution assays we determined higher antibacterial effect of three Salvia spp. and by evaluating the leakage of 260 nm absorbing material we detected effect of extracts and, namely, of essential oils on the disruption of cytoplasmic membrane. The evaluation of in vitro interactions between plant extracts and oxacillin described in terms of fractional inhibitory concentration (FIC) indices revealed synergistic or additive effects of plant extracts and clearly synergistic effects of essential oil from Salvia officinalis with oxacillin in methicillin-resistant Staphylococcus epidermidis.

Growth-Inhibiting and morphostructural effects of constituents identified in Asarum heterotropoides root on human intestinal bacteria

BACKGROUND

The growth-inhibiting and morphostructural effects of seven constituents identified in Asarum heterotropoides root on 14 intestinal bacteria were compared with those of the fluoroquinolone antibiotic ciprofloxacin.

METHOD

A microtiter plate-based bioassay in sterile 96-well plates was used to evaluate the minimal inhibitory concentrations (MICs) of the test materials against the organisms.

RESULTS

δ-3-Carene (5) exhibited the most potent growth inhibition of Gram-positive bacteria (Clostridium difficile ATCC 9689, Clostridium paraputrificum ATCC 25780, Clostridium perfringens ATCC 13124, and Staphylococcus aureus ATCC 12600) and Gram-negative bacteria (Escherichia coli ATCC 11775 and Bacteroides fragilis ATCC 25285) (minimal inhibitory concentrations (MIC), 0.18-0.70 mg/mL) except for Salmonella enterica serovar Typhimurium ATCC 13311 (MIC, 2.94 mg/mL). The MIC of methyleugenol (2), 1,8-cineole (3), α-asarone (4), (-)-asarinin (6), and pellitorine (7) was between 1.47 and 2.94 mg/mL against all test bacteria (except for compound 2 against C. difficile (0.70 mg/mL); compounds 1 (23.50 mg/mL) and 4 (5.80 mg/mL) against C. paraputricum; compounds 2 (5.80 mg/mL), 4 (12.0 mg/mL), and 7 (0.70 mg/mL) against C. perfringens); compound 1 against E. coli (7.20 mg/mL) and S. enterica serovar Typhimurium (12.0 mg/mL). Overall, all of the constituents were less potent at inhibiting microbial growth than ciprofloxacin (MIC, 0.063-0.25 mg/ mL). The lactic acid-producing bacteria (four bifidobacteria and two lactobacilli) and one acidulating bacterium Clostridium butyricum ATCC 25779 were less sensitive and more susceptible than the five harmful bacteria and two nonpathogenic bacteria (B. fragilis and E. coli) to the constituents and to ciprofloxacin, respectively. Beneficial Gram-positive bacteria and harmful and nonpathogenic Gram-negative bacteria were observed to have different degrees of antimicrobial susceptibility to the constituents, although the antimicrobial susceptibility of the harmful Gram-positive bacteria and the harmful and nonpathogenic Gram-negative bacteria was not observed. Scanning electron microscopy observations showed different degrees of physical damage and morphological alteration to both Gram-positive and Gram-negative bacteria treated with α-asarone, δ-3-carene, pellitorine, or ciprofloxacin, indicating that they do not share a common mode of action.

CONCLUSION

A. heterotropoides root-derived materials described merit further study as potential antibacterial products or lead molecules for the prevention or eradication from humans from diseases caused by harmful intestinal bacteria.

Antibacterial Activity of Rhodomyrtus tomentosa (Aiton) Hassk. Leaf Extract against Clinical Isolates of Streptococcus pyogenes

Ethanol extract of Rhodomyrtus tomentosa (Aiton) Hassk. leaf was evaluated for antibacterial activity against 47 clinical isolates of Streptococcus pyogenes. The extract exhibited good anti-S. pyogenes activity against all the tested isolates with similar minimum inhibitory concentration (MIC, 3.91-62.5 μg mL(-1)) and minimum bactericidal concentration (MBC, 3.91-62.5 μg mL(-1)) ranges. No surviving cells were detected at 16 h after treatment with 8 × MIC of the extract. The extract-treated cells demonstrated no lysis and cytoplasmic leakage through the bacterial membrane. Electron micrographs further revealed that the extract did not cause any dramatic changes on the treated cells. Rhodomyrtone, an isolated compound, exhibited good anti-S. pyogenes activity (14 isolates), expressed very low MIC (0.39-1.56 μg mL(-1)) and MBC (0.39-1.56 μg mL(-1)) values. Rhodomyrtus tomentosa leaf extract and rhodomyrtone displayed promising antibacterial activity against clinical isolates of S. pyogenes.

Growth-inhibiting effects of Paeonia lactiflora root steam distillate constituents and structurally related compounds on human intestinal bacteria

The growth-inhibiting activities of Paeonia lactiflora (Paeoniaceae) root steam distillate constituents and structurally related compounds against nine harmful intestinal bacteria and eight lactic acid-producing bacteria were compared with those of two antibiotics, amoxicillin and tetracycline. Thymol, α-terpinolene, (-)-perilla alcohol and (1R)-(-)-myrtenol exhibited high to extremely high levels of growth inhibition of all the harmful bacteria, whereas thymol and α-terpinolene (except for Lactobacillus casei ATCC 393) inhibited the growth of all the beneficial bacteria (MIC, both 0.08-0.62 mg mL(-1)). Tetracycline and amoxicillin exhibited extremely high level of growth inhibition of all the test bacteria (MIC, <0.00002-0.001 mg mL(-1)). 1,8-Cineole, geraniol, (-)-borneol, (1S,2S,5S)-(-)-myrtanol, nerol, (S)-(-)-β-citronellol and (±)-lavandulol also exhibited inhibitory activity but with differing specificity and levels of activity. Structure-activity relationship indicates that structural characteristics, such as geometric isomerism, degrees of saturation, types of functional groups and types of carbon skeleton, appear to play a role in determining the growth-inhibiting activity of monoterpenoids. Global efforts to reduce the level of antibiotics justify further studies on naturally occurring P. lactiflora root-derived materials as potential preventive agents against various diseases caused by harmful intestinal bacteria such as clostridia.

Activity of (-)alpha-bisabolol against Leishmania infantum promastigotes

Many of the drugs used to treat leishmaniasis are associated with numerous adverse effects. Agents of natural origin have shown activity against different parasites. With this background, an in vitro study was conducted on the activity of (-)alpha-bisabolol, the principal component of Chamomilla recutita essential oil, against Leishmania infantum promastigotes, the main species responsible for human leishmaniasis in Spain. At the two highest concentrations tested (1000 and 500mug/ml), (-)alpha-bisabolol and pentamidine (control agent) achieved 100% inhibition of L. infantum promastigote. These in vitro data can be considered promising in support of the therapeutic use of (-)alpha-bisabolol preparations to treat leishmaniasis caused by L. infantum species.

Chemical Composition and Antimicrobial Activity of Essential Oil of Bupleurum montanum and B. plantagineum

The hydrodistilled oils from the aerial parts of Bupleurum montanum and B. plantagineum, which are endemic to North Africa, including Algeria, were analyzed by gas chromatography-mass spectrometry (GC-MS). Ninety-eight compounds were detected in the oil of B. montanum, representing 98.6% of the total oil, and 68 in the oil of B. plantagineum, representing 99.8% of the total. Megastigma-4,6-(E),8(2)-triene was the major constituent of B. montana oil (25.3%). Other important compounds were myrcene, α-pinene and benzyl tiglate. Conversely, the major constituents of the oil of B. plantagineum were α-pinene (31.9%), cis-chrysanthenyl acetate (28.2%), and myrcene (24.8%), followed by the monoterpene hydrocarbon limonene (5.1%). The mutagenic, antiplasmodial and antimicrobial activities of the essential oils were individually evaluated against eleven microorganisms, using the agar diffusion method, by determination of MIC values. The investigated oils exhibited moderate antimicrobial activity. Maximum activity of the oils was observed against Nocardia asteroides, Staphylococcus aureus and Enterococcus faecalis. Fungicidal activity against Candida albicans was also found for both oils.

Rhodomyrtone: a new candidate as natural antibacterial drug from Rhodomyrtus tomentosa

Rhodomyrtone [6,8-dihydroxy-2,2,4,4-tetramethyl-7-(3-methyl-1-oxobutyl)-9-(2-methylpropyl)-4,9-dihydro-1H-xanthene-1,3(2H)-di-one] from Rhodomyrtus tomentosa (Aiton) Hassk. displayed significant antibacterial activities against gram-positive bacteria including Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Staphylococcus epidermidis, Streptococcus gordonii, Streptococcus mutans, Streptococcus pneumoniae, Streptococcus pyogenes, and Streptococcus salivarius. Especially noteworthy was the activity against MRSA with a minimum inhibitory concentration (MIC) and a minimum bactericidal concentration (MBC) ranging from 0.39 to 0.78 microg/ml. As shown for S. pyogenes, no surviving cells were detected within 5 and 6h after treatment with the compound at 8MBC and 4MBC concentrations, respectively. Rhodomyrtone displays no bacteriolytic activity, as determined by measurement of the optical density at 620 nm. A rhodomyrtone killing test with S. mutans using phase contrast microscopy showed that this compound caused a few morphological changes as the treated cells were slightly changed in color and bigger than the control when they were killed. Taken together, the results support the view that rhodomyrtone has a strong bactericidal activity on gram-positive bacteria, including major pathogens.

GC/MS evaluation of thyme (Thymus vulgaris L.) oil composition and variations during the vegetative cycle

Capillary GC/MS analysis based on polar and non-polar columns has been applied to evaluation of the volatile oils hydrodistilled from thyme (Thymus vulgaris L.) plants. The adopted methodology has been used to monitor seasonal variations in the composition of the oil obtained from thyme herbs harvested at different periods during the plant vegetative and life cycles. Oils from thyme plants of young (2 years) and old (5 years) cultivations have been evaluated from four and two collections, respectively, effected throughout May/December growth period. Generally, the oil was found to be rich in the active monoterpene phenols (thymol and carvacrol) and their corresponding monoterpene hydrocarbon (HC) precursors (p-cymene and gamma-terpinene), which collectively showed synchronized patterns of variation during the different collection periods and in different seasons. The oil from old plant collected in May/June period (0.15% v/w) was characterized by significantly lower levels of monoterpene HCs (mainly gamma-terpinene) and the highest levels of the oxygenated monoterpenes (linalool and borneol), monoterpene phenols (mainly thymol) and their derivatives (mainly carvacrol methyl ether), sesquiterpenes (mainly beta-caryophyllene) and their oxygenated derivatives (e.g. caryophyllene oxide) in comparison with all other samples. A characteristic presence of camphor and thymodihydroquinone was also observed in the old plant oils. On the other hand, the young plant, collected in June/July just before the end of the vegetative cycle, provided the best oil yield (1.2%) with also the highest % content of the monoterpene phenols (thymol: 51.2% and carvacrol: 4%). This latter growth period can represent the best harvest time of young thyme plants in order to obtain an essential oil with better quality and quantity.

Mechanism of action of Melaleuca alternifolia (tea tree) oil on Staphylococcus aureus determined by time-kill, lysis, leakage, and salt tolerance assays and electron microscopy

The essential oil of Melaleuca alternifolia (tea tree) has broad-spectrum antimicrobial activity. The mechanisms of action of tea tree oil and three of its components, 1,8-cineole, terpinen-4-ol, and alpha-terpineol, against Staphylococcus aureus ATCC 9144 were investigated. Treatment with these agents at their MICs and two times their MICs, particularly treatment with terpinen-4-ol and alpha-terpineol, reduced the viability of S. aureus. None of the agents caused lysis, as determined by measurement of the optical density at 620 nm, although cells became disproportionately sensitive to subsequent autolysis. Loss of 260-nm-absorbing material occurred after treatment with concentrations equivalent to the MIC, particularly after treatment with 1,8-cineole and alpha-terpineol. S. aureus organisms treated with tea tree oil or its components at the MIC or two times the MIC showed a significant loss of tolerance to NaCl. When the agents were tested at one-half the MIC, only 1,8-cineole significantly reduced the tolerance of S. aureus to NaCl. Electron microscopy of terpinen-4-ol-treated cells showed the formation of mesosomes and the loss of cytoplasmic contents. The predisposition to lysis, the loss of 260-nm-absorbing material, the loss of tolerance to NaCl, and the altered morphology seen by electron microscopy all suggest that tea tree oil and its components compromise the cytoplasmic membrane.