The olive compound 4-hydroxytyrosol inactivates Staphylococcus aureus bacteria and Staphylococcal Enterotoxin A (SEA)

The foodborne pathogen Staphylococcus aureus produces the virulent staphylococcal enterotoxin A (SEA), a single chain protein which consists of 233 amino acid residues with a molecular weight of 27078 Da. SEA is a superantigen that is reported to contribute to animal (mastitis) and human (emesis, diarrhea, atopic dermatitis, arthritis, and toxic shock) syndromes. Changes in the native structural integrity may inactivate the toxin by preventing molecular interaction with cell membrane receptor sites of their host cells. In the present study, we evaluated the ability of the pure olive compound 4-hydroxytyrosol and a commercial olive powder called Hidrox-12, prepared by freeze-drying olive juice, to inhibit S. aureus bacteria and SEA's biological activity. Dilutions of both test substances inactivated the pathogens. Two independent cell assays (BrdU incorporation into newly synthesized DNA and glycyl-phenylalanyl-aminofluorocoumarin proteolysis) demonstrated that the olive compound 4-hydroxytyrosol also inactivated the biological activity of SEA at concentrations that were not toxic to the spleen cells. However, efforts to determine inhibition of the toxin by Hidrox-12 were not successful because the olive powder was cytotoxic to the spleen cells at concentrations found to be effective against the bacteria. The results suggest that food-compatible and safe antitoxin olive compounds can be used to inactivate both pathogens and toxins produced by the pathogens. Practical Application: The results of this study suggest that food-compatible and safe antitoxin olive compounds can be used to reduce both pathogens and toxins produced by the pathogens in foods.     

GaN etch rate and surface roughness evolution in Cl2/Ar based inductively coupled plasma etching

Cl₂/Ar based inductively coupled plasma (ICP) etching of GaN is investigated using photoresist mask in a consequential restricted domain of pressure < 1.2 Pa and radio frequency (RF) sample power < 100 W, for selective mesa etching. The etch characteristics and root-mean-square (rms) surface roughness are studied as a function of process parameters viz. process pressure, Cl₂ percentage in total flow rate ratio, and RF sample power at a constant ICP power, to achieve moderate GaN etch rate with anisotropic profiles and smooth surface morphology. The etch rate and resultant surface roughness of etched surface increased with pressure mainly due to dominant reactant limited etch regime. The etch rate and surface roughness show strong dependence on RF sample power with the former increasing and the later decreasing with the applied RF sample power up to 80 W. The process etch yield variation with applied RF sample power is also reported. The studied etch parameters result in highly anisotropic mesa structures with Ga rich etched surface.     

Recipes for antimicrobial wine marinades against Bacillus cereus, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica

ABSTRACT:  We have evaluated bactericidal activities against Bacillus cereus , Escherichia coli O157:H7, Listeria monocytogenes , and Salmonella enterica of several antimicrobial wine recipes, each consisting of red or white wine extracts of oregano leaves with added garlic juice and oregano oil. Dose-response plots were used to determine the percentage of the recipes that resulted in a 50% decrease in colony-forming units (CFU) at 60 min (BA₅₀). Studies designed to optimize antibacterial activities of the recipes demonstrated that several combinations of the naturally occurring plant-derived ingredients rapidly inactivated the above mentioned 4 foodborne pathogens. We also showed that (a) incubation temperature affected activities in the following order: 37 °C > 21 °C > 4 °C; (b) varying the initial bacterial concentrations from 10³ to 10⁴ to 10⁵ CFU/well did not significantly affect BA₅₀ values; (c) storage of 3 marinades up to 2 mo did not change their effectiveness against Salmonella enterica ; and (d) polyphenolic compounds isolated by chromatography from red wine exhibited exceptional activity at nanogram levels against 2 strains of Bacillus cereus . These observations suggest that antimicrobial wine formulations have the potential to improve the microbiological safety of foods.     

Bactericidal Activities of Health‐Promoting,Food‐Derived Powders Against the Foodborne Pathogens Escherichia coli,Listeria monocytogenes,Salmonella enterica,and Staphylococcus aureus

We evaluated the relative bactericidal activities (BA₅₀) of 10 presumed health‐promoting food‐based powders (nutraceuticals) and, for comparison, selected known components against the following foodborne pathogens: Escherichia coli O157:H7, Salmonella enterica, Listeria monocytogenes, and Staphylococcus aureus. The relative activities were evaluated using quantitative bactericidal activity [(BA₅₀ value, defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in colony forming units]. The BA₅₀ values were determined by fitting the data to a sigmoidal curve by regression analysis using concentration–antimicrobial response data. Antimicrobial activity is indicated by a low BA₅₀ value; meaning less material is needed to kill 50% of the bacteria. Olive pomace, olive juice powder, and oregano leaves were active against all 4 pathogens, suggesting that they behave as broad‐spectrum antimicrobials. All powders exhibited strong antimicrobial activity against S. aureus. The following powders showed exceptionally high activity against S. aureus (as indicated by the low BA₅₀ values shown in parentheses): apple skin extract (0.002%); olive pomace (0.008%); and grape seed extract (0.016%). Listeria bacteria were also highly susceptible to apple skin extract (0.007%). The most active substances provide candidates for the evaluation of antimicrobial effectiveness in human food and animal feed. Practical Application : Plant‐derived health‐promoting food supplements, high in bioactive compounds, are candidates for use as antimicrobials in food.     

Bactericidal activities of plant essential oils and some of their isolated constituents against Campylobacter jejuni,Escherichia coli,Listeria monocytogenes,and Salmonella enterica

An improved method of sample preparation was used in a microplate assay to evaluate the bactericidal activity levels of 96 essential oils and 23 oil compounds against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica obtained from food and clinical sources. Bactericidal activity (BA50) was defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in CFU relative to a buffer control. Twenty-seven oils and 12 compounds were active against all four species of bacteria. The oils that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.009) were marigold, ginger root, jasmine, patchouli, gardenia, cedarwood, carrot seed, celery seed, mugwort, spikenard, and orange bitter oils; those that were most active against E. coli (with BA50 values ranging from 0.046 to 0.14) were oregano, thyme, cinnamon, palmarosa, bay leaf, clove bud, lemon grass, and allspice oils; those that were most active against L monocytogenes (with BA50 values ranging from 0.057 to 0.092) were gardenia, cedarwood, bay leaf, clove bud, oregano, cinnamon, allspice, thyme, and patchouli oils; and those that were most active against S. enterica (with BA50 values ranging from 0.045 to 0.14) were thyme, oregano, cinnamon, clove bud, allspice, bay leaf, palmarosa, and marjoram oils. The oil compounds that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.034) were cinnamaldehyde, estragole, carvacrol, benzaldehyde, citral, thymol, eugenol, perillaldehyde, carvone R, and geranyl acetate; those that were most active against E. coli (with BA50 values ranging from 0.057 to 0.28) were carvacrol, cinnamaldehyde, thymol, eugenol, salicylaldehyde, geraniol, isoeugenol, citral, perillaldehyde, and estragole; those that were most active against L monocytogenes (with BA50 values ranging from 0.019 to 0.43) were cinnamaldehyde, eugenol, thymol, carvacrol, citral, geraniol, perillaldehyde, carvone S, estragole, and salicylaldehyde; and those that were most active against S. enterica (with BA50 values ranging from 0.034 to 0.21) were thymol, cinnamaldehyde, carvacrol, eugenol, salicylaldehyde, geraniol, isoeugenol, terpineol, perillaldehyde, and estragole. The possible significance of these results with regard to food microbiology is discussed.     

Antimicrobial activities of tea catechins and theaflavins and tea extracts against Bacillus cereus

We evaluated the antimicrobial activities of seven green tea catechins and four black tea theaflavins, generally referred to as flavonoids, as well as the aqueous extracts (infusions) of 36 commercial black, green, oolong, white, and herbal teas against Bacillus cereus (strain RM3190) incubated at 21 degrees C for 3, 15, 30, and 60 min. The results obtained demonstrate that (i) (-)-gallocatechin-3-gallate, (-)-epigallocatechin-3-gallate, (-)-catechin-3-gallate, (-)-epicatechin-3-gallate, theaflavin-3, 3'-digallate, theaflavin-3'-gallate, and theaflavin-3-gallate showed antimicrobial activities at nanomolar levels; (ii) most compounds were more active than were medicinal antibiotics, such as tetracycline or vancomycin, at comparable concentrations; (iii) the bactericidal activities of the teas could be accounted for by the levels of catechins and theaflavins as determined by high-pressure liquid chromatography; (iv) freshly prepared tea infusions were more active than day-old teas; and (v) tea catechins without gallate side chains, gallic acid and the alkaloids caffeine and theobromine also present in teas, and herbal (chamomile and peppermint) teas that contain no flavonoids are all inactive. These studies extend our knowledge about the antimicrobial effects of food ingredients.     

Antibacterial activities of phenolic benzaldehydes and benzoic acids against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica

We evaluated the bactericidal activities of 35 benzaldehydes, 34 benzoic acids, and 1 benzoic acid methyl ester against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica when these compounds were substituted on the benzene ring with 0, 1, 2, or 3 hydroxy (OH) and/or methoxy (OCH3) groups in a pH 7.0 buffer. Dose-response plots were used to determine the percentage of the sample that induced a 50% decrease in CFU after 60 min (BA50). Of the 70 compounds tested, 24 were found to be active against all four pathogens, and additional 4, 10, and 12 were found to be active against three, two, and one of the pathogens, respectively. C. jejuni was approximately 100 times as sensitive as the other three pathogens. The 10 compounds that were most active against the four pathogens (with average BA50 values ranging from 0.026 to 0.166) and are candidates for studies of activity in foods or for disinfections were 2,4,6-trihydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,3,4-trihydroxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, 2,3-dihydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-2,6-dimethoxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde. and 2-hydroxybenzaldehyde. Comparison of the chemical structures of the test compounds and their activities revealed that (i) the aldehyde (CHO) group was more active than the carboxyl (COOH) group whether or not OH groups were present; (ii) compounds were most active with trisubstituted OH > disubstituted OH > monosubstituted OH; (iii) for disubstituted derivatives, 2-OH enhanced activities were exhibited by benzaldehyde but not by benzoic acid; (iv) compounds were more active with OH than with OCH3, irrespective of the position of substitution on the benzene ring; (v) compounds with mixed OH and OCH3 groups exhibited variable results, i.e., in some cases OCH3 groups enhanced activity and in other cases they did not; (vi) methoxybenzoic acids were largely inactive; and (vii) gallic acid was 20 times as active against S. enterica at pH 7.0 as it was at pH 3.7, suggesting that the ionization of its OH groups may enhance bactericidal activity.     

Antimicrobial Wine Formulations Active Against the Foodborne Pathogens Escherichia coli O157: H7 and Salmonella enterica

ABSTRACT:  We developed wine formulations containing plant essential oils and oil compounds effective against foodborne pathogenic bacteria Escherichia coli O157:H7 and Salmonella enterica. HPLC was used to determine maximum solubility of antimicrobials in wines as well as amounts of antimicrobials extracted by wines from commercial oregano and thyme leaves. Activity of essential oils (cinnamon, lemongrass, oregano, and thyme) and oil compounds (carvacrol, cinnamaldehyde, citral, and thymol) in wines were evaluated in terms of the percentage of the sample that resulted in a 50% decrease in the number of bacteria (BA₅₀). The ranges of activities in wines (30 min BA₅₀ values) against S. enterica/E. coli were carvacrol, 0.0059 to 0.010/0.011 to 0.021; oregano oils, 0.0079 to 0.014/0.022 to 0.031; cinnamaldehyde, 0.030 to 0.051/0.098 to 0.13; citral, 0.033 to 0.038/0.060 to 0.070; lemongrass oil, 0.053 to 0.066/0.059 to 0.071; cinnamon oil 0.038 to 0.057/0.066 to 0.098; thymol, 0.0086 to 0.010/0.016 to 0.022; and thyme oil, 0.0097 to 0.011/0.033 to 0.039. Detailed studies with carvacrol, the main component of oregano oil, showed that antibacterial activity was greater against S. enterica than against E. coli and that wine formulations exhibited high activities at low concentrations of added antimicrobials. The results suggest that wines containing essential oils/oil compounds, added or extracted from oregano or thyme leaves, could be used to reduce pathogens in food and other environments.