Micrococcus Flavus Research Articles

In vitro antibacterial activity of the crude methanol extract of Woodfordia fruticosa Kurz. flower (Lythraceae)

The antibacterial activity of the crude methanol extract of Woodfordia fruticosa Kurz. flower was evaluated at two different concentrations by the agar well diffusion method. The methanol extract of the flower exhibited antibacterial activity at varied levels except against Bacillus subtilis and Micrococcus flavus. The methanol extract was most active against Pseudomonas pseudoalcaligenes. The extract was more active against Gram-negative bacteria as compared to Gram-positive. The inhibitory effect of the extract was compared with standard antibiotics, amoxicillin and ciprofloxacin.

Molecular and biochemical characterizations of human oral lactobacilli as putative probiotic candidates

The objective of this study was to characterize the lactobacilli from the human oral cavity as a potential source of probiotic strains. Samples were collected from four different locations within the oral cavity: surface of healthy tooth, oral mucous membrane, surface of tooth decay and deep tooth decay. On the basis of morphological and biochemical properties eight categories were formed and 26 isolates were selected for further characterization. The isolates were determined as Lactobacillus sp. using primers specific for 16S rDNA. Sequencing of 16S rDNA genes and repetitive sequence-based polymerase chain reactions were used for determination to species and subspecies levels. Predominant species were Lactobacillus fermentum, Lactobacillus plantarum, Lactobacillus salivarius and Lactobacillus paracasei subsp. paracasei, while Lactobacillus acidophilus, Lactobacillus cellobiosus, Lactobacillus delbrueckii subsp. lactis and Lactobacillus gasseri were also present. The isolates Lactobacillus salivarius BGHO1, Lactobacillus fermentum BGHO36 and BGHO64, Lactobacillus gasseri BGHO89 and Lactobacillus delbrueckii subsp. lactis BGHO99 exhibited antagonistic action on the growth of Staphylococcus aureus, Enterococcus faecalis, Micrococcus flavus, Salmonella enteritidis, Streptococcus pneumoniae and Streptococcus mutans, but not on growth of Candida albicans. Moreover, the isolates L. salivarius BGHO1 and L. gasseri BGHO89 were tolerant to low pH and high concentration of bile salts. Taken together, these findings imply that L. salivarius BGHO1 and L. gasseri BGHO89 might be subjects for additional investigation as potential probiotic strains.

Micrococcus flavus sp. nov., isolated from activated sludge in a bioreactor

Bacterial strain LW4(T) was isolated from activated sludge of a wastewater-treatment bioreactor. Cells of strain LW4(T) were Gram-positive cocci, with a diameter of 0.7-1.0 microm. Colonies produced on LB agar plates were yellow, smooth, circular and 0.5-1.5 mm in diameter. Strain LW4(T) was aerobic and grew over the temperature range 26-34 degrees C and pH range 5-9, with optimal growth at 30.5-31.5 degrees C and pH 6.0-6.2. The cell-wall peptidoglycan of strain LW4(T) contained amino acid residues of lysine, glutamic acid, alanine, glycine and aspartic acid. The most abundant cellular fatty acids of strain LW4(T) were anteiso-C(15 : 0) (32.15 %) and iso-C(15 : 0) (31.65 %). Major respiratory quinones were MK-8(H(2)) (57.3 %) and MK-7(H(2)) (32.9 %). The DNA G+C content was 71.4 mol% (T(m)). 16S rRNA gene sequence analysis indicated that strain LW4(T) was phylogenetically related to members of the genus Micrococcus, with similarities ranging from 96.5 to 97.3 %. Levels of DNA-DNA relatedness of strain LW4(T) to Micrococcus luteus DSM 20030(T), Micrococcus lylae DSM 20315(T) and Micrococcus antarcticus AS 1.2372(T) were 55, 48 and 36 %, respectively. Based on these results, it is concluded that strain LW4(T) represents a novel species of the genus Micrococcus, for which the name Micrococcus flavus sp. nov. is proposed. The type strain is strain LW4(T) (=CGMCC 1.5361(T)=JCM 14000(T)).

Marine Algae

This study was done to investigate the antimicrobial potentiality of the marine algae collected from different coastal regions of Gujarat and screened for the same. Twenty-six marine algae belonging to Rhodophyceae, Chlorophyceae and Phaeophyceae were screened for their potential antibacterial activity against five clinically important bacterial strains, namely Bacillus cereus, Micrococcus flavus, Citrobacter freundii, Klebsiella pneumoniae and Pseudomonas testosterone. Acetone and methanol were used for extraction; and the extracted yield was more when the solvent used was methanol. The antibacterial activity was done by both Agar disc diffusion method and Agar ditch method. The five bacterial strains showed varied response towards marine algal extracts. The most susceptible bacteria was B. cereus followed by K. pneumoniae and C. freundii while the most resistant bacteria were M. flavus and P. testosteroni. Among the 26 algae screened, E. intestinalis was the most potent alga and thus, this alga was selected for further studies. E. intestinalis was extracted in petroleum ether, 1,4-dioxan, acetone, methanol and DMF, and their antibacterial activity was studied against the above-stated five bacterial strains using agar disc method. Maximum extractive value of E. intestinalis was in methanol (2.05%) and minimum was in acetone (0.38%). The most susceptible bacteria was K. pneumoniae and maximum antibacterial activity was shown by petroleum ether extract and minimum was shown by 1,4-dioxan extract. The most resistant bacteria were M. flavus and C. freundii. The MIC values of E. intestinalis extracts ranged from 2500-9.765 microg/0.5 ml against B. cereus and K. pneumoniae. From these results it is concluded that the acetone extract of E. intestinalis is the most potent extract and can be used as a lead molecule in drug discovery in inhibiting some of the bacterial strains. E. intestinalis can be used as a promising novel marine antimicrobial agent in the coming years.

Characterization and antimicrobial activity of natural isolate Lactococcus lactis subsp. lactis BGSM1-19

The strain Lactococcus lactis subsp. lactis BGSM1-19, isolated from traditionally homemade white cheese, produces two bacteriocins: lactococcin B-like bacteriocin named bacteriocin BacSMa and bacteriocin BacSMb which have shown similarity with lacticin RM. Plasmid curing resulted in a low yield (0.33%) of BacSMa- BacSMas and BacSMa- BacSMas, BacSMb-, BacSMbs derivatives. The bacteriocin biosynthesis was observed in the logarithmic phase of growth and the production plateau was reached after 8 h of incubation at 30oC, when the culture entered the early stationary phase. Biochemical characterization showed that strain BGSM1-19 retained antimicrobial activity within the pH range of 1 to 12 or after treatment at 100oC for 15 min. However, bacteriocin activity was completely lost after treatment with different proteolytic enzymes. The strain BGSM1-19 contains five plasmids. Plasmid curing indicated that genes coding for bacteriocins synthesis and immunity seem to be located on plasmids. BGSM1-19 exhibited antimicrobial activity against some pathogenic bacteria such as Salmonella paratyphi, Micrococcus flavus, Pseudomonas aeruginosa and Staphylococcus aureus.

Free-radical scavenging capacity and antimicrobial activity of wild edible mushroom from Turkey

Antioxidant capacity and antimicrobial activities of Ramaria flava (Schaeff) Quel. (RF) extracts obtained with ethanol were investigated in this study. Four complementary test systems; namely DPPH free radical scavenging,
-carotene/linoleic acid systems, total phenolic compounds and total flavonoid concentration have been used. Inhibition values of R. flava extracts, BHA and -tocopherol standards were found to be 94.7, 98.9 and 99.2%, respectively, at 160ƒEg/ml. When compared the inhibition levels of ethanol extract of R. flava and standards in linoleic acid system, it was observed that the higher the concentration of both RF ethanol extract and the standards the higher the inhibition effect. Total flavonoid amount was 8.27}0.28 ƒEg mg-1 quercetin equivalent while the total phenolic compound amount was 39.83}0.32 ƒEg mg-1 pyrocatechol equivalent in the ethanolic extract. The ethanol extract of R. flava inhibited the growth of Gram-positive bacteria better than Gram-negative bacteria and yeast. The crude extract showed no antibacterial activity against Pseudomonas aeruginosa, Escherichia coli, Morganella morganii and Proteus vulgaris. The antimicrobial activity profile of R. flava against tested strains indicated that Micrococcus flavus, Micrococcus luteus and Yersinia enterocolitica was the most susceptible bacteria of all the test strains. R. flava was found to be inactive against Candida albicans.

The antibiotic activity of some Brazilian medicinal plants

The antibiotic activities of the ethanol extracts from 16 species of plants used in Brazilian folk medicine have been determined against Staphylococcus aureus, Micrococcus flavus, Bacillus cereus, B. subtilis, Salmonella enteretidis, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Serratia marcescens, Mycobacterium phlei, M. smegmatis and M. fortuitum, and the yeasts Candida albicans and C. krusei. Among 32 extracts assayed, only those from Lafoensia pacari and Pterodon polygalaeflorus showed activity against the bacterial strains, and none were active against the yeasts. The ethanolic extract from the leaves of L. pacari showed minimum inhibitory concentration (MIC) values of 312.5 to 2500, 250, 625 and 1250 mg/mL, respectively, against eight different Gram-positive strains of Staphylococcus aureus, the Gram-negative Proteus mirabilis and the acid-fast bacilli Mycobacterium phlei, M. fortuitum and M. smegmatis. The ethanolic extract from the stem of L. pacari showed an MIC value of 625 mg/mL against S. aureus. Chemical analysis revealed that the crude extracts contained tannins, steroids, phenols, flavonoids, triterpenes and saponins: the activities were sufficiently high to present the possibility of future identification of the active components by bioassay-guided fractionation and purification.

Synergetic activity of nisin with cell-free supernatant of Bacillus licheniformis ZJU12 against food-borne bacteria

Antibacterial activity of nisin and cell-free supernatant of Bacillus licheniformis ZJU12 (CFSb), separately and in combination, against three food-borne bacteria: Micrococcus flavus, Bacillius cereus and Staphylococcus aureus was determined. M. flavus was more sensitive to nisin and CFSb than other two indicator strains in the MIC tests. Synergetic activity of nisin and CFSb was found against all the three indicator strains in the checkerboard microtiter test and the time-kill test. The combination had the most notable antibacterial activity against B. cereus as determined by the fractional inhibitory concentration index (FICI). The antibacterial activity of nisin and CFSb separately began within the first 30 min, while their synergetic activity was observed after 4 h.

Potential of lactic acid bacteria isolated from specific natural niches in food production and preservation

Autochthonous strains of lactic acid bacteria (LAB) have been isolated from traditionally homemade cheeses collected from specific ecological localities across Serbia and Montenegro. Genetic and biochemical analysis of this LAB revealed that they produce bacteriocins, proteinases and exopolysaccharides. LAB produces a variety of antimicrobial substances with potential importance for food fermentation and preservation. Apart from the metabolic end products, some strains also secrete antimicrobial substances known as bacteriocins. Among the natural isolates of LAB from homemade cheeses, bacteriocin producers were found in both lactococci and lactobacilli. Lactococcus lactis subsp. lactis BGMN1–5 was found to produce three narrow spectrum class II heat-stable bacteriocins. In addition to bacteriocin production, BGMN1–5 synthesized a cell envelope-associated proteinase (CEP) and shows an aggregation phenotype. Another isolate, L. lactis subsp. lactis BGSM1–19 produces low molecular mass (7 kDa) bacteriocin SM19 that showed antimicrobial activity against Staphylococcus aureus, Micrococcus flavus and partially against Salmonella paratyphi. Production of bacteriocin reaches a plateau after 8 h of BGSM1–19 growth. Bacteriocin SM19 retained activity within the wide pH range from 1 to 12 and after the treatment at 100 °C for 15 min. Among collection of lactobacilli, the isolate Lactobacillus paracasei subsp. paracasei BGSJ2–8 produces heat-stable bacteriocin SJ (approx. 5 kDa) polypeptide. It retained activity after treatment for 1 h at 100 °C, and in the pH range from 2 to 11. In addition to isolates from cheeses, bacteriocin-producing human oral lactobacilli were detected. Most of them showed antimicrobial activity against streptococci, staphylococci and micrococci, but not against Candida. Isolate BGHO1 that showed the highest antimicrobial activity was determined as L. paracasei. Interestingly, Lactobacillus helveticus BGRA43, which was isolated from the human intestine showed strong activity against Clostridium sporogenes, but it was not possible to detect any bacteriocin production in this isolate by using standard procedures. Further analysis of antimicrobial activity revealed that BGRA43 has a relatively broad spectrum. Lactobacilli resistant to nisin were also detected among natural isolates. They produce bacteriocins, which have no activity against nisin producing lactococci.

Bioactive Components of the Traditionally used Mushroom Podaxis pistillaris

In the course of an ethnobotanical study on fungi used in Yemeni ethnomedicine the fungus Podaxis pistillaris (Podaxales, Podaxaceae, Basidiomycetes) was found to exhibit antibacterial activity against Staphylococcus aureus, Micrococcus flavus, Bacillus subtilis, Proteus mirabilis, Serratia marcescens and Escherichia coli. In the culture medium of P. pistillaris three epidithiodiketopiperazines were identified by activity-guided isolation. Based on spectral data (NMR, ESI-MS and DCI-MS) their identity was established as epicorazine A (1), epicorazine B (2) and epicorazine C (3, antibiotic F 3822), which have not been reported as constituents of P. pistillaris previously. It is assumed that the identified compounds contribute to the antibacterial activity of the extract.

Fluorescent reagents for in vitro studies of lipid-linked steps of bacterial peptidoglycan biosynthesis: derivatives of UDPMurNAc-pentapeptide containing d-cysteine at position 4 or 5

UDPMurNAc-L-Ala-gamma-D-Glu-X-D-Ala-DAla (X = L-Lys or m-DAP) is the cytoplasmic precursor for the lipid-linked cycle of bacterial peptidoglycan biosynthesis, consisting of at least four enzymatic reactions, which are targets for antibacterial agents. Fluorescent derivatives of the UDPMurNAc-pentapeptide labelled at the 3rd, 4th, and 5th position of the peptide chain were prepared chemoenzymatically, in order to study the reactions catalysed by enzymes in this cycle. Derivatives labelled on the epsilon-amino group of the 3rd amino acid (N-dansyl, N-fluorescamine and N-phthalaldehyde) were prepared by chemical modification. Two methods were developed for preparation of analogues of UDPMurNAc-pentapeptide containing D-cysteine at position 4 or 5: either by MurF-catalysed ligation of the UDPMurNAc-tripeptide to synthetic D-Ala-D-Cys or D-Cys-D-Ala dipeptides; or by enzymatic synthesis of D-Ala-D-Cys by ligase VanD. D-Cys-containing UDPMurNAc-pentapeptides were labelled with pyrene maleimide, to give 4-pyrene and 5-pyrene labelled derivatives. The fluorescent UDPMurNAc-pentapeptides were processed as substrates by Escherichia coli MraY or E. coli membranes, giving 1.5-150-fold changes in fluorescence upon transformation to lipid intermediate I. Subsequent processing to lipid intermediate II gave rise only to small changes in fluorescence. Pyrene-labelled lipid intermediates I and II can be generated using Micrococcus flavus membranes, enabling the study of the later lipid-linked steps.

Clarification and sterilization of raw depectinized apple juice by ceramic ultrafiltration membranes

AbstractRaw depectinized apple juice was clarified and sterilized in a cross‐flow pilot scale ultrafiltration system using ceramic tubular membranes (MEMBRALOX®, Pall) with mean pore size of 100 nm. The permeate flux significantly decreased with time until a steady‐state was established. An increase in filtration pressure increased the permeate flux while there is an optimum pressure (about 0.85 bar) above which the increase of pressure does not increase the flux significantly. The higher the cross‐flow velocity was, the higher was the transmembrane flux. When the operating temperature increased, the permeation rate increased subsequently. Analytical measurement showed that suspended solids and turbidity could almost be removed by the ceramic ultrafiltration membrane, but pH, acidity, sugar and soluble solid content of the juices showed no significant change. The bacteria challenge tests with Micrococcus flavus showed that the logarithm value of the bacteria reduction rate came up to above 9 in the cross‐flow tubular ceramic system. When the permeate was collected in sterile bottles in a laminar flow shell and kept at 4 °C, 8 °C, 25 °C and 35 °C, for 28 days, the apple juice experienced minimal changes in physicochemical properties at lower temperatures of 4 °C, or 8 °C. Copyright © 2005 Society of Chemical Industry

Characterization and enhanced production of enterocin HJ35 byEnterococcus faecium HJ35 isolated from human skin

A strain named as HJ35 was isolated from the skin of sixty-five men and fourteen women for acne therapy, in order to find an effective antimicrobial agent againstPropionibacterium acnes. Isolate HJ35 was identified asEnterococcus faecium based on 16 rDNA sequence and produced enterocin HJ35 having antimicrobial activities against most lactic acid bacteria,Enterococcus spp.,Staphylococcus aureus, S. epidermidis, Clostridium perfringens, some bacilli,Micrococcus flavus, Listeria monocytogenes, L. ivanovii, Escherichia coli, Pseudomonas fluorescens andPropionibacterium acnes, in the modified well diffusion method. Especially, enterocin HJ35 showed a bactericidal activity againstPropionibacterium acnes P1. The antimicrobial activity of enterocin HJ35 was disappeared completely with the use of protease XIV. But enterocin HJ35 activity is very stable at high temperature (up to 100°C for 30 min), in wide range of pH 3.0∼9.0), and by treatment with organic solvents. The apparent molecular mass of enterocin HJ35 was estimated to be approximately 4∼4.5 kDa on detection of its bactericidal activity after SDS-PAGE. In batch fermentation ofE. faecium HJ35, enterocin HJ35 was produced at the midlog growth phase, and its maximum production was obtained up to 2,300 AU/mL at the late stationary phase. By employing fed-batch fermentation, the enhanced production of enterocin HJ35 was achieved up to 12,800 AU/mL by feeding with 10 g/L glucose or 6 g/L lactate.

Production, Purification, and Characterization of Micrococcin GO5, a Bacteriocin Produced by Micrococcus sp. GO5 Isolated from Kimchi

Strain GO5, a bacteriocin-producing bacterium, was isolated from green onion kimchi and identified as Micrococcus sp. The bacteriocin, micrococcin GO5, displayed a broad spectrum of inhibitory activity against a variety of pathogenic and nonpathogenic microorganisms, as tested by the spot-on-lawn method; its activity spectrum was almost identical to that of nisin. Micrococcin GO5 was inactivated by trypsin (whereas nisin was not) and was completely stable at 100°C for 30 min and in the pH range of 2.0 to 7.0. Micrococcin GO5 exhibited a typical mode of bactericidal activity against Micrococcus flavus ATCC 10240. It was purified to homogeneity through ammonium sulfate precipitation, ultrafiltration, and CM-Sepharose column chromatography. The molecular mass of micrococcin GO5 was estimated to be about 5.0 kDa by tricine–sodium dodecyl sulfate–polyacrylamide gel electrophoresis and in situ activity assay with the indicator organism. The amino acid sequence of micrococcin GO5 lacks lanthionine and β-methyllanthionine and is rich in hydrophobic amino acids and glycine, providing the basis for the high heat stability of this bacteriocin. The N-terminal amino acid sequence of micrococcin GO5 is Lys-Lys-Ser-Phe-Cys-Gln-Lys, and no homology to bacteriocins reported previously was observed in the amino acid composition or N-terminal amino acid sequence. Based on the physicochemical properties, small molecular size, and inhibition of Listeria monocytogenes, micrococcin GO5 has been placed with the class II bacteriocins, but its broad spectrum of activity differs from that of other bacteriocins in this class.

Resistance of Gram-positive bacteria to nisin is not determined by Lipid II levels

Lipid II is essential for nisin-mediated pore formation at nano-molar concentrations. We tested whether nisin resistance could result from different Lipid II levels, by comparing the maximal Lipid II pool in Micrococcus flavus (sensitive) and Listeria monocytogenes (relatively insensitive) and their nisin-resistant variants, with a newly developed method. No correlation was observed between the maximal Lipid II pool and nisin sensitivity, as was further corroborated by using spheroplasts of nisin-resistant and wild-type strains of M. flavus, which were equally sensitive to nisin.

Overexpression, purification, and characterization of ATP-NAD kinase of Sphingomonas sp. A1

The NAD kinase gene ( nadK) of Sphingomonas sp. A1 was cloned and then overexpressed in Escherichia coli, and the gene product (NadK) was purified from the E. coli cells through five steps with a 25% yield of activity. NadK was a homodimer of 32 kDa subunits, utilized ATP or other nucleoside triphosphates, but not inorganic polyphosphates, as phosphoryl donors for the phosphorylation of NAD, most efficiently at pH 8.0 and 50–55 °C, and was designated as ATP-NAD kinase (NadK). NadK showed no NADH kinase activity and was slightly inhibited by NADP(H). Precursors for NAD biosynthesis such as quinolinic acid, nicotinic acid mononucleotide, nicotinic acid adenine dinucleotide, and nicotinic acid had no effect on the NadK activity, as observed in the cases of the NAD kinases of Micrococcus flavus, Mycobacterium tuberculosis, and E. coli. Taken together with the report that the NAD kinase of Bacillus subtilis is activated by quinolinic acid [J. Bacteriol. 185 (2003) 4844], it is indicated that the regulatory patterns of NAD kinases differ even among bacterial NAD kinases.

Bovicin HJ50, a novel lantibiotic produced by Streptococcus bovis HJ50

A bacteriocin-producing strain was isolated from raw milk and named Streptococcus bovis HJ50. Like most bacteriocins produced by lactic acid bacteria, bovicin HJ50 showed a narrow range of inhibiting activity. It was sensitive to trypsin, subtilisin and proteinase K. Bovicin HJ50 was extracted by n-propanol and purified by SP Sepharose Fast Flow, followed by Phenyl Superose and Sephadex G-50. Treatment of Micrococcus flavus NCIB8166 with bovicin HJ50 revealed potassium efflux from inside the cell in a concentration-dependent manner. The molecular mass of bovicin HJ50 was determined to be 3428.3 Da. MS analysis of DTT-treated bovicin HJ50 suggested that bovicin HJ50 contains a disulfide bridge. The structural gene of bovicin HJ50 was cloned by nested PCR based on its N-terminal amino acid sequence. Sequence analysis showed that it encodes a 58 aa prepeptide consisting of an N-terminal leader sequence of 25 aa and a C-terminal propeptide domain of 33 aa. Bovicin HJ50 shows similarity to type AII lantibiotics. Chemical modification using an ethanethiol-containing reaction mixture showed that two Thr residues are modified.

Essential oil analysis and antimicrobial activity of eight Stachys species from Greece

The volatile composition of eight Stachys species has been studied. The investigated taxa were St. alopecuros (L.) Bentham., St. scardica (Griseb.) Hayek, St. cretica L. ssp. cretica, St. germanica L. ssp. heldreichii (Boiss.) Hayek, St. recta L., St. spinulosa L., St. euboica Rech. and St. menthifolia Vis., growing wild in Greece. The essential oils were obtained by hydrodistillation in a modified Clevenger-type apparatus, and their analyses were performed by GC and GC–MS. Identification of the substances was made by comparison of mass spectra and retention indices with literature records. Sesquiterpene hydrocarbons were shown to be the main group of constituents of all taxa. Furthermore, the obtained essential oils were tested against the following six bacteria: Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 35210), Bacillus subtilis (ATCC 10907), Bacillus cereus (clinical isolates) , Micrococcus flavus (ATCC 10240), Staphylococcus epidermidis (ATCC 2228), as well as against the following five fungi: Aspergillus niger (ATCC 6275), Penicillium ochrochloron (ATCC 9112), Epidermophyton floccosum (clinical isolates), Candida albicans (clinical isolates) and Trichophyton mentagrophytes (clinical isolates). The tested essential oils showed better activity against bacterial species than against fungi. Pseudomonas aeruginosa was the most resistant strain, as none of the essential oils was active against this strain. The essential oil of St. scardica has been proven most active against both bacteria and fungi.

A coating for use as an antimicrobial and antioxidative packaging material incorporating nisin and α-tocopherol

A 3-mm thick nisin and/or α-tocopherol coating at a concentration of 3% was applied on a paper using a binder medium of vinyl acetate-ethylene copolymer to confer an antimicrobial and antioxidative property for use in the food packaging industry. The migration of nisin and α-tocopherol from the coating to a model emulsion composed of 66% water and 32% paraffin oil with 2% emulsifier was measured, and this was linked to the suppression of microbial growth and oxidative deterioration in the emulsion and in milk cream at 10 °C. The nisin migrated more slowly than α-tocopherol, and reached 9.3% of the total concentration incorporated in the coating, with α-tocopherol reaching an equilibrium level of 5.7%. The migration of each of the additives was not affected by the presence of the other. Incorporation of nisin in the coating was effective in inhibiting Micrococcus flavus, and α-tocopherol incorporation retarded lipid oxidation in the model emulsion and in the milk cream. Thus, the combination of nisin and α-tocopherol in the coating conferred both antimicrobial and antioxidative properties. However, it did not provide any further synergistic antimicrobial and antioxidative effect when compared to a single additive alone.

Antimicrobial and antioxidant activities of three Mentha species essential oils.

The present study describes the antimicrobial activity and free radical scavenging capacity (RSC) of essential oils from Mentha aquatica L., Mentha longifolia L., and Mentha piperita L. The chemical profile of each essential oil was determined by GC-MS and TLC. All essential oils exhibited very strong antibacterial activity, in particularly against Esherichia coli strains. The most powerful was M. piperita essential oil, especially towards multiresistant strain of Shigella sonei and Micrococcus flavus ATTC 10,240. All tested oils showed significant fungistatic and fungicidal activity [expressed as minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) values, respectively], that were considerably higher than those of the commercial fungicide bifonazole. The essential oils of M. piperita and M. longifolia were found to be more active than the essential oil of M. aquatica. Especially low MIC (4 microL/mL) and MFC (4 microL/mL) were found with M. piperita oil against Trichophyton tonsurans and Candida albicans (both 8 microL/mL). The RSC was evaluated by measuring the scavenging activity of the essential oils on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and OH radicals. All examined essential oils were able to reduce DPPH radicals into the neutral DPPH-H form, and this activity was dose-dependent. However, only the M. piperita oil reduced DPPH to 50 % (IC50 = 2.53 microg/mL). The M. piperita essential oil also exhibited the highest OH radical scavenging activity, reducing OH radical generation in the Fenton reaction by 24 % (pure oil). According to GC-MS and TLC (dot-blot techniques), the most powerful scavenging compounds were monoterpene ketones (menthone and isomenthone) in the essential oils of M. longifolia and M. piperita and 1,8-cineole in the oil of M. aquatica.