Browsing by Person "Stewart, J."

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Antimicrobial properties of plant essential oils and essences against five important food-borne pathogens
(Wiley, 1998) Smith-Palmer, A.; Stewart, J.; Fyfe, Lorna
The antimicrobial properties of 21 plant essential oils and two essences were investigated against five important food-borne pathogens, Campylobacter jejuni, Salmonella enteritidis, Escherichia coli, Staphylococcus aureus and Listeria monocytogenes. The oils of bay, cinnamon, clove and thyme were the most inhibitory, each having a bacteriostatic concentration of 0075% or less against all five pathogens. In general, Gram-positive bacteria were more sensitive to inhibition by plant essential oils than the Gram-negative bacteria. Campylobacter jejuni was the most resistant of the bacteria investigated to plant essential oils, with only the oils of bay and thyme having a bacteriocidal concentration of less than 1%. At 35 C, L. monocytogenes was extremely sensitive to the oil of nutmeg. A concentration of less than 001% was bacteriostatic and 005% was bacteriocidal, but when the temperature was reduced to 4 C, the bacteriostatic concentration was increased to 05% and the bacteriocidal concentration to greater than 1%.
Influence of sub-inhibitory concentrations of plant essential oils on the production of enterotoxins A and B and alpha toxin by Staphylococcus aureus
(Society for General Microbiology, 2004-10) Smith-Palmer, A.; Stewart, J.; Fyfe, Lorna
The data presented show the ability of subinhibitory concentrations of plant essential oils to influence the production of enterotoxins A and B and alpha-toxin by Staphylococcus aureus. Subinhibitory concentrations of the oils of bay, clove, cinnamon, nutmeg and thyme had no significant effect on the overall quantity of extracellular protein produced. Haemolysis due to alpha-toxin was significantly reduced after culture with all five plant essential oils. This reduction was greatest with the oils of bay, cinnamon and clove. These three oils also significantly decreased the production of enterotoxin A; the oils of clove and cinnamon also significantly decreased the production of enterotoxin B.
Inhibition of listeriolypin O and phosphatidylcholine - specific phospholipase C production in Listeria monocytogeres by subinhibitory concentrations of plant essential oils
(Society for General Microbiology, 2002-07) Smith-Palmer, A.; Stewart, J.; Fyfe, Lorna
Successful infection by Listeria monocytogenes is dependent upon a range of bacterial extracellular proteins including a cytolysin termed listeriolysin O and phosphatidylcholine-specific phospholipase C. Five plant essential oils--bay, clove, cinnamon, nutmeg and thyme--significantly reduced the production of listeriolysin O by L. monocytogenes. The greatest change was observed after culture with oil of thyme, which reduced haemolysis to 52.1 haemolytic units (HU)/ml compared with 99.8 HU/ml observed with the control. Oil of clove was the only oil that also significantly reduced phosphatidylcholine-specific phospholipase C activity. These changes were observed despite the oils causing no change to the final bacterial concentration or total extracellular protein concentration.
The potential application of plant essential oils as natural food preservatives in soft cheese
(Elsevier, 2001-08) Smith-Palmer, A.; Stewart, J.; Fyfe, Lorna
Investigations were carried out to assess the efficiency of four plantessentialoils; bay, clove, cinnamon and thyme as naturalfoodpreservatives. The effect of the plantessentialoils at concentrations of 0·1, 0·5 and 1% was studied in low-fat and full-fat softcheese against Listeria monocytogenes and Salmonella enteritidis at 4° and 10°C respectively, over a 14-day period. The composition of the cheese was shown to be an important factor in determining the effectiveness of the plantessentialoils. In the low-fat cheese, all four oils at 1% reduced L. monocytogenes to ≤1·0 log10cfu ml−1. In contrast, in the full-fat cheese, oil of clove was the only oil to achieve this reduction. Oil of thyme proved ineffective against S. enteritidis in the full-fat cheese, yet was equally as effective as the other three oils in the low-fat cheese, reducing S. enteritidis to ≤1·0 log10cfu ml−1from day 4 onwards. It is concluded that selected plantessentialoils can act as potent inhibitors of L. monocytogenes and S. enteritidis in a food product.