Chemical composition,antimicrobial potential against cariogenic bacteria and cytotoxic activity of Tunisian Nigella sativa essential oil and thymoquinone

We investigate in this work the chemical composition by GC–EIMS, the antibacterial and the cytotoxic activities of Tunisian Nigella sativa essential oil and its bioactive compound, thymoquinone, were tested against various clinical cariogenic bacteria (n = 30). Eighty-four compounds were identified in the essential oil. The major one was p-cymene (49.48%) whereas thymoquinone represented only 0.79%. The essential oil (2.43 mg/disc) containing only 3.35 μg of thymoquinone showed pronounced dose dependant antibacterial activity against Streptococcus mitis, Streptococcus mutans, Streptococcus constellatus and Gemella haemolysans (15.5 ± 0.707 mm). However, pure thymoquinone compound (150 μg/disk) was active against all the studied strains especially S. mutans and S. mitis (24.5 ± 0.71 and 22 ± 1.41 mm inhibition zones, respectively).     

Correlation analysis between phenolic levels of Brazilian propolis extracts and their antimicrobial and antioxidant activities

Propolis extracts are currently used for the treatment of oronasal infections and as antioxidant agents. Ethanolic commercial Brazilian propolis extracts were assayed for their ability to inhibit the growth of Staphylococcus aureus and also for their ability to scavenge DPPH radicals. These activities were correlated with their total phenolic and flavonoid levels. In one group of extracts there was a strong linear relationship between total phenol contents and the measured activities, while in the other group this relationship was weaker. It was also found that flavonoid levels had a greater influence on the antioxidant activity of these extracts than on their antimicrobial profiles.     

Bioassay-guided isolation and identification of antifungal components from propolis against Penicillium italicum

The present study was aimed at identification of antifungal components against Penicillium italicum from Chinese propolis with bioassay-guided fractionation technique. Propolis ethanolic extract (PEE) was separated and purified by liquid–liquid extraction and thin layer chromatography (TLC) and the most active band was subjected to HPLC–MS/MS to identify the antifungal compounds. The results showed PEE and its fractions had strong antifungal activity against P. italicum. Among the fractions of PEE partitioned by petroleum ether, ethyl acetate, n-butanol and water, ethyl acetate fraction (E-Fr) exhibited the most effective activity against P. italicum. Further bioautographic TLC assay showed Band I, with Rf value of 0.70, had an inhibitive zone, which showed the strongest antifungal activity and completely inhibited the growth of P.italicum at 200 mg/L. Bioactive components found in Band I were further identified as pinobanksin, pinocembrine, chrysin and galangin. This study exhibited Chinese propolis and its main flavonoids was potential natural alternatives for the control of citrus blue mould caused by P.italicum.     

Isolation of red wine components with anti-adhesion and anti-biofilm activity against Streptococcus mutans

Red wine is a widely consumed beverage with multiple beneficial effects on human health. In the present paper, the anticaries properties of red wine were studied in vitro and ex vivo. Our in vitro findings shows that dealcoholised red wine, besides exerting antibacterial activity, strongly interferes with Streptococcus mutans adhesion to saliva-coated hydroxyapatite (sHA) beads, promotes its detachment from sHA, and powerfully inhibits in vitro biofilm formation. The main components responsible for such activities were found to be proanthocyanidins. The ability of red wine to inhibit ex vivoS. mutans biofilm formation on the occlusal surface of natural human teeth also was demonstrated.     

Food preservative based on propolis: Bacteriostatic activity of propolis polyphenols and flavonoids upon Escherichia coli

Propolis was tested as food preserver, due its recognized bactericidal and bacteriostatic properties. Furthermore, most propolis components are natural constituents of food and recognized as safe substances. Fifteen propolis from Santa Fe, Argentine in 20% w/w ethanolic extracts, were tested upon Escherichia coli ATCC 25922 by agar diffusion and plate culture methods. Considering propolis physicochemical characteristics and inhibitory effects, tested samples were classified in three groups. A minimum inhibitory concentration mean value of 14.3 ± 6 mg soluble compounds/ml of the most active propolis was capable of inhibiting 10⁵ cfu/ml cellular concentration. Such extract had 32.31% total soluble compounds (2.1% coumaric + siringic acids, 5.16% quercetin, 0.47 apigenine, 8.15 galangine, 7.2 caffeic acid + crisine and 9.23% no-identified phenolics compounds). By relating the zone of growth inhibition with extracts concentration, a linear response was obtained. On the propolis samples tested, a single value of the minimum inhibitory concentration could not be established. Those values were strongly dependent on propolis composition and botanical origin. The propolis extracts tested, may successfully inhibit the E. coli development in vitro, and consequently may be useful as natural food preserver.     

Separation of an effective fraction from turmeric against Streptococcus mutans biofilms by the comparison of curcuminoid content and anti-acidogenic activity

Turmeric has long been used as a colouring and flavouring agent for foods. Curcuminoids are the main component of turmeric and have a range of pharmacological activities. In this study, a fraction that could show anti-biofilm activity was separated from turmeric, based on a comparison of curcuminoid content and anti-acidogenic activity against Streptococcus mutans, and the effects of the separated fraction and curcuminoids on the adherence ability of S. mutans and the physiological ability of S. mutans biofilms were examined at sub-minimum inhibitory concentration (MIC) levels. The separated fraction and curcuminoids had inhibitory effects on the sucrose-dependant adherence of S. mutans to saliva-coated hydroxyapatite (sHA) discs and the acidogenicity and aciduricity of S. mutans biofilms. These results suggest that the separated turmeric fraction and its components, curcuminoids, may be useful for controlling dental biofilms and subsequent dental caries formation.     

Antimicrobial activity of leptospermone and its derivatives against human intestinal bacteria

The anaerobic growth inhibiting activity of the essential oil of Leptospermum scoparium seeds against intestinal bacteria was evaluated in vitro. The essential oil at 5.0 mg/disc strongly (+++) inhibited the growth of Clostridium difficile and Clostridium perfringens, but did not inhibit the growth of Bifidobacterium breve, Bifidobacterium longum, Escherichia coli, or Lactobacillus casei. Spectroscopic analyses revealed that the active component of the essential oil was leptospermone. Leptospermone strongly inhibited the growth of C. difficile and C. perfringens at 1.0 mg/disc and moderately inhibited their growth at 0.5 mg/disc. However, leptospermone did not inhibit the growth of B. breve, B. longum, and L. casei. When compared with the leptospermone derivatives, 1,2,3-cyclohexanetrione-1,3-dioxime exerted strong inhibition against C. perfringens and moderate inhibition against C. difficile at 0.5 mg/disc, whereas the other derivatives exerted weak or no growth inhibition against all bacteria tested. Taken together, these results indicate that cyclohexanetrione is required for triketone derivatives to inhibit the growth of C. difficile and C. perfringens. These findings indicate that L. scoparium seed-derived materials and 1,2,3-cyclohexanetrione-1,3-dioxime are naturally occurring antimicrobial agents that could be useful in the development of new agents for the specific control of C. difficile and C. perfringens.     

Biochemistry,genetics, and applications of exopolysaccharide production in Streptococcus thermophilus: a review

Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides. These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., "ropy" polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable "ropy" or viscous texture to fermented milk products. Recent work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese, but they are not phage-proof. As our understanding of the genetics, physiology, and functionality of bacterial exopolysaccharides continues to improve, novel applications for polysaccharides and polysaccharide-producing cultures are likely to emerge inside and outside the dairy industry. This article provides an overview of biochemistry, genetics, and applications of exopolysaccharide production in S. thermophilus.     

The inhibitory effect of Plectranthus barbatus and Plectranthus ecklonii leaves on the viability,glucosyltransferase activity and biofilm formation of Streptococcus sobrinus and Streptococcus mutans

Aqueous extracts of Plectranthus barbatus and Plectranthus ecklonii are traditionally used as anti-inflammatory and anti-fungal agents. The effect of these extracts and of its main component, rosmarinic acid, on the viability of the cariogenic bacteria, Streptococcus sobrinus and Streptococcus mutans, was determined by MIC and MBC. The influence of these extracts on the biofilm formation as well as on the inhibition of glucosyltransferase enzyme, produced by these species, was also analysed. Aqueous extracts of P. barbatus and P. ecklonii were stronger inhibitors than rosmarinic acid. MIC values of 3.8 and 4.7 mg/ml for S. sobrinus and 2.9 and 5.0 for S. mutans were obtained, while rosmarinic acid presented MIC values of 8.4 and 7.3 mg/ml. P. barbartus, P. ecklonii and rosmarinic acid presented MBC values of 9.5, 9.0 and 12.0 mg/ml for S. sobrinus, and 9.5, 10.0 and 12.5 mg/ml for S. mutans. The inhibition of biofilm formation by P. barbatus, P. ecklonii and rosmarinic acid presented IC₅₀ values of, respectively, 0.6, 1.0 and 3.1 mg/ml for S. sobrinus and 1.4 and 2.7 and 1.3 mg/ml for S. mutans. The glucosyltransferase inhibition activity by theses extracts and rosmarinic acid was calculated and IC₅₀ values presented were, respectively, 1.1, ca 1.2 and 2.1 mg/ml for S. sobrinus and 3.1, 1.6 and 3.9 mg/ml for S. mutans were obtained. These extracts may be useful in the prevention of dental carie.     

Antimicrobial activity of the essential oils of Brazilian species of the genus Cunila against foodborne pathogens and spoiling bacteria

The essential oils from aerial parts of six Brazilian species of the genus Cunila Mill. (Lamiaceae) currently used in beverages and food preparation, and in folk medicine, were obtained by steam distillation and analyzed by GC and GC/MS. The main components of the oils were: Cunila galioides citral (citral −77.9%), C. galioides menthene (mentha-trans-2,8-dienol −20.0%, limonene −13.6%, trans-ocimene −13.0%), C. incisa (1,8-cineole −42.9%, α-terpineol −14.0%), C. spicata (1,8-cineole −47.9%, α-terpineol −37.5%), C. menthoides (menthene −77.8%), C. angustifolia (sabinene −41.4%, γ-terpinene −11.4%), and C. microcephala (menthofuran −94.90%). These oils were screened for antibacterial activity against 15 bacterial species. The oil of C. galioides citral efficiently controlled the growth of Bacillus sp., L. monocytogenes, S. aureus, A. hydrophila, and E. faecalis, showing both contact and gaseous activity. Although less efficient, the other essential oils studied were effective against Bacillus species, S. aureus, and other specific bacteria. MIC and MCC values support their popular use, and indicate that they can be an efficient alternative for the control of foodborne and spoiling bacteria.     

The effect of untreated and enzyme-treated commercial dairy powders on the growth and adhesion of Streptococcus mutans

Dental caries is a common bacterial infection, but the progression of this disease can be delayed by preventing initial attachment of cariogenic bacteria such as Streptococcus mutans to tooth surfaces. This study firstly compares the effect of untreated (UT) and enzyme-treated (ET) dairy powders on the adherence of S. mutans to hydroxylapatite (HA), an analogue of tooth enamel. A fluorescence-based method was used to quantify adherence of S. mutans to HA both in the presence (S-HA) and absence (PBS-HA) of saliva. Secondly, binding of proteins present in the test materials to HA was quantified using bicinchonic acid assays and SDS-PAGE. In addition, the effect of UT and ET dairy powders on growth of S. mutans was examined using an optical-density based assay. UT acid whey protein concentrate (WPC) 80, sweet WPC80, buttermilk powder (BMP) and cream powder (CP) significantly (P < 0.05) inhibited adhesion of S. mutans at ≥31.25 μg mL⁻¹ in the presence and absence of saliva. ET dairy powders were less effective inhibitors of adhesion, but ET sweet WPC80 significantly (P < 0.05) inhibited growth of S. mutans at ≥0.6 mg mL⁻¹. Therefore, due to their adherence- and growth-inhibitory properties, dairy powders may be beneficial in the treatment of dental caries.     

Antimicrobial activity of catechol isolated from Diospyros kaki Thunb. roots and its derivatives toward intestinal bacteria

The growth-inhibiting activities of the methanol extract of Diospyros kaki Thunb. roots were examined on the growth of Bifidobacterium breve, B. longum, Clostridium difficile, Clostridium perfringes, Escherichia coli, and Lactobacillus casei. In addition, the biologically active component of D. kaki roots was purified using silica gel column chromatography and HPLC. The active component was characterised as catechol by spectroscopic analyses. The antimicrobial activity of the isolated catechol varied according to the dose and bacterial strains tested. Catechol significantly (++++) inhibited the growth of C. perfringens at 2.0 mg/disc, and moderately (++) inhibited its growth at 0.25 mg/disc. At a dose of 5.0 mg/disc, catechol significantly inhibited the growth of C. difficile and moderately inhibited the growth of E. coli. However, this isolate did not inhibit the growth of bifidobacteria and lactobacilli. When various functional groups were added to the catechol, selective growth-inhibiting activity against harmful intestinal bacteria was observed in response to treatment with low concentrations. Taken together, these findings indicate that D. kaki root-isolated catechol and its derivatives (4-nitrocatechol, 4-tert-butylcatechol, tetrabromocatechol) could be useful as preventive agents against diseases caused by harmful intestinal bacteria.     

Selectivity and antimicrobial action of bovine lactoferrin derived peptides against wine lactic acid bacteria

In this study, the antibacterial activities of a bovine Lactoferrin pepsin hydrolysate (LFH) and a synthetic peptide derived from bovine lactoferricin (LfcinB_17–31) have been evaluated against Oenococcus oeni and three additional lactic acid bacteria (LAB) known to cause spoilage during winemaking processes. Inhibition of bacterial growth was demonstrated in vitro in synthetic broth media (MRS) for both LFH and LfcinB_17–31. The bactericidal activity of the synthetic peptide was also assayed and found to vary depending on the bacterial species and the matrix in which exposure to peptide occurred (either MRS broth or white must). Specificity of LfcinB_17–31 for Lactobacillus brevis, Pediococcus damnosus, and O. oeni was demonstrated in must fermentation experiments in which these three LAB co-existed with the winemaking Saccharomyces cerevisiae T73 in the presence of the peptide. Finally, fermentation experiments also showed that LfcinB_17–31 at inhibitory concentrations did not alter either fermentation kinetics or specific enological parameters.     

Species,roasting degree and decaffeination influence the antibacterial activity of coffee against Streptococcus mutans

Coffee beverage has been associated with antibacterial activity against Streptococcus mutans, a cariogenic bacterium. This study aimed at identifying natural compounds in coffee that contribute to such activity and investigate the influence of species, roasting and decaffeination on it. Coffee chemical compounds and aqueous extracts of green and roasted regular and decaffeinated Coffea arabica and Coffea canephora beans were tested. MIC, biofilm inhibition and biofilm reduction results were correlated with the concentration of coffee compounds in the extracts. 5-Caffeoylquinic acid, trigonelline and caffeic acid solutions showed bacteriostatic activity (MIC = 0.8 mg/mL). Lighter and regular extracts showed higher inhibitory activity than darker and decaffeinated extracts, with an inverse correlation between bacterial colony-forming units and roasting degree. Only regular C. canephora extracts showed biofilm formation inhibition. The joint effect of chlorogenic acids, trigonelline and caffeine or other compounds removed by decaffeination seems to be one of the causes for coffee antibacterial activity against S. mutans.     

Histamine formation by histamine-forming bacteria and yeast in mustard pickle products in Taiwan

The occurrence of histamine, histamine-forming bacteria and yeast were tested in 37 mustard pickle products sold in both retail markets and supermarkets in southern Taiwan. Aerobic plate count (APC), total coliform, and Escherichia coli were also tested for microbiological quality. Salt content, pH value, titratable acidity and sulphite content were determined for quality of mustard pickle products. Only one retail market sample and one supermarket sample had 8.9 and 7.4 mg histamine per 100 g products, although the average content for each of the nine biogenic amines was less than 2 mg/100 g. Ten histamine-forming bacterial strains and 6 histamine-producing yeast strains capable of producing 8.7 to 1260 ppm of histamine in trypticase soy broth (TSB) supplemented with 1% l-histidine (TSBH) were identified as Staphylococcus capitis (four strains),Staphylococcus pasteuri (two strains), Enterobacter cloacae (four strains), Candida glabrata (two strains) and Candida rugosa (four strains). S. capitis, which was previously reported to be halotolerant, was a potent histamine-former, capable of producing more than 1000 ppm of histamine in TSBH in the presence of 0.5–10% NaCl. The numbers of the aerobic plate count (APC) in all samples were below the Taiwanese regulatory level of 5 log CFU/g. None of the samples contained total coliform or E. coli. The values of pH, salt content, titratable acidity and sulphite content in all samples ranged from 3.8% to 5.0%, 2.0% to 10.0%, 0.21% to 1.18% and <2.0–1876 ppm, respectively.     

Antibacterial activity of the extracts from the fruit rinds of Garcinia cowa and Garcinia pedunculata against food borne pathogens and spoilage bacteria

The crude hexane and chloroform extracts from the fruit rinds of Garcinia cowa and Garcinia pedunculata were studied for their antibacterial activity against some foodborne pathogens and spoilage bacteria such as Bacillus cereus, Bacillus coagulans, Bacillus subtilis, Staphylococcus aureus and Escherichia coli. The minimum inhibitory concentrations (MICs) of the extracts determined by the agar dilution method were ranging from 15 to 500 μg/ml and 300 to 1250 μg/ml for G. cowa and G. pedunculata, respectively. However, the hexane and chloroform extracts from the fruit rinds of G. cowa exhibited marked inhibitory effect against all the test organisms and were more effective than that of G. pedunculata extracts. The antibacterial activity of all the extracts was more pronounced against the tested Gram-positive bacteria than the tested Gram-negative bacterium. Furthermore, this study is the first report on the in vitro antibacterial activity of extracts from the fruit rinds of G. cowa and G. pedunculata.     

Detection of ethanol in food: A new biosensor based on bacteria

A microbial biosensor for determination of ethanol has been developed. The microbial ethanol biosensor comprises a Methylobacterium organophilium-immobilized eggshell membrane and an oxygen (O₂) electrode. The microbial biosensor responds linearly to ethanol in the range 0.050–7.5 mM with a detection limit of 0.025 mM (S/N = 3) and the response time is 100 s. The optimal loading of bacterial cells on the biosensor membrane is 40 mg (wet weight). The optimal working conditions for the microbial biosensor are pH 7.0 phosphate buffer (50 mM) at 20–25 °C. The interference test, operational and storage stability of the biosensor are studied in detail. Finally, the biosensor is applied to determine the ethanol contents in various alcohol samples and the results are comparable to that obtained by a gas chromatographic method. Our work demonstrates that the proposed microbial biosensor is a reliable method to determine the ethanol content in wine samples.     

Isolation of lactic acid bacteria with inhibitory activity against pathogens and spoilage organisms associated with fresh meat

The use of lactic acid bacteria (LAB) as protective cultures in vacuum-packed chill-stored meat has potential application for assuring and improving food quality, safety and market access. In a study to identify candidate strains suitable for evaluation in a meat model, agar-based methods were employed to screen 181 chilled meat and meat process-related LAB for strains inhibitory to pathogens and spoilage organisms of importance to the meat industry. Six meat-derived strains, including Lactobacillus sakei and Lactococcus lactis, were found to be inhibitory to one or more of the target strains Listeria monocytogenes, Brochothrix thermosphacta, Campylobacter jejuni and Clostridium estertheticum. The inhibitory agents appeared to be either cell-associated or molecules released extracellularly with bacteriocin-like properties. Variations detected in the antimicrobial activity of LAB associated with changes to test parameters such as substrate composition underlined the importance of further in situ evaluation of the inhibitory strains in stored meat trials.     

Antibacterial peptides from barbel muscle protein hydrolysates: Activity against some pathogenic bacteria

Peptides obtained by enzymatic hydrolysis of fish proteins exhibit not only nutritional but also biological properties of dietary uses, or even therapeutic potential. The objective of the present study was to isolate and characterize peptides from the protein hydrolysates of barbel muscle with antibacterial activity against Gram-positive (Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Micrococcus luteus and Bacillus cereus) and Gram-negative (Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterobacter sp.) bacteria. Barbel muscle protein hydrolysates (BMPHs), obtained by treatment with Alcalase^® (DH = 6.6%), was fractionated by size exclusion chromatography on a Sephadex G-25 and purified by reversed-phase high performance liquid chromatography (RP-HPLC). The molecular masses and amino acid sequences of these peptides were determined using ESI–MS and ESI–MS/MS, respectively. Eleven peptides in F_II-1, F_II-2, F_II-3 and F_II-4 sub-fractions separated by RP-HPLC were identified. The most active peptide fraction (F_II-3) contained three peptides: Ala–Ala–Ala–Leu; Ala–Ala–Gly–Gly–Val and Ala–Ala–Val–Lys–Met.