George-John E. Nychas

Bio: George-John E. Nychas is an academic researcher from Agricultural University of Athens. The author has contributed to research in topics: Food spoilage & Population. The author has an hindex of 73, co-authored 275 publications receiving 17802 citations. Previous affiliations of George-John E. Nychas include National and Kapodistrian University of Athens & University of Bath.

A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol.

Abstract: Aims: The minimum inhibitory concentration (MIC) of oregano essential oil (OEO) and two of its principle components, i.e. thymol and carvacrol, against Pseudomonas aeruginosa and Staphylococcus aureus was assessed by using an innovative technique. The mechanism of action of the above substances was also investigated. Methods and Results: The applied technique uses 100-well microtitre plate and collects turbidimetric growth data. To produce the inhibition profiles, a wide range of concentrations were tested for each of the three compounds, as well as for carvacrol‐thymol mixtures. Following a specific mathematical analysis of the observed inhibition profiles from all compounds, it was suggested that mixtures of carvacrol and thymol gave an additive effect and that the overall inhibition by OEO can be attributed mainly to the additive antimicrobial action of these two compounds. Addition of low amounts of each additive: (a) increased permeability of cells to the nuclear stain EB, (b) dissipated pH gradients as indicated by the CFDA-SE fluorescent probe irrespective of glucose availability and (c) caused leakage of inorganic ions. Conclusions: Mixing carvacrol and thymol at proper amounts may exert the total inhibition that is evident by oregano essential oil. Such inhibition is due to damage in membrane integrity, which further affects pH homeostasis and equilibrium of inorganic ions. Significance and Impact of the Study: The knowledge of extent and mode of inhibition of specific compounds, which are present in plant extracts, may contribute to the successful application of such natural preservatives in foods, since certain combinations of carvacrol‐ thymol provide as high inhibition as oregano essential oil with a smaller flavour impact.

Natural antimicrobials from plants

Abstract: Food preservation is becoming more complex. New food products are being introduced onto the market. Generally these require longer shelf-lives and greater assurance of freedom from foodborne pathogenic organisms. The search for new substances to be used in food preservation is hampered by regulatory restrictions. Consequently a great deal of time and money may be required to develop a new chemical preservative and to get it approved especially in view of the public pressure against chemical additives in general. Such obstacles provide new opportunities for those seeking alternative routes in the search for new food preservatives. The excessive use of chemical preservatives, some of which are suspect because of their supposed or potential toxicity, has resulted in increasing pressure on food manufacturers to either completely remove chemical preservatives from their food products or to adopt more ‘natural’ alternatives for the maintenance or extension of a product’s shelf life. There is considerable interest in the possible use of such natural alternatives as food additives either to prevent the growth of foodborne pathogens or to delay the onset of food spoilage. Many naturally occurring compounds, such as phenols (phenolic acid, polyphenols, tannins), and organic acids (acetic, lactic, citric) have been considered in this context. Many spices and herbs and extracts possess antimicrobial activity, almost invariably due to the essential oil fraction (Deans and Ritchie, 1987). Thus the essential oils of citrus fruits exhibit antibacterial activity to foodborne bacteria (Dabbah et al., 1970) and moulds (Akgul and Kivanc, 1989) so too have the essential oils of many other plants such as oregano, thyme (Salmeron et al., 1990;Paster et al., 1990), sage, rosemary, clove, coriander etc. (Farag et al., 1989; Aureli et al., 1992; Stecchini et al., 1993). The antibacterial and antimycotic effects of garlic and onion have been well documented also (Mantis et al., 1978; Sharma et al., 1979; Saleem and Al-Delaimy, 1982; Conner and Beuchat, 1984a,b).

Plant Products as Antimicrobial Agents

Abstract: The use of and search for drugs and dietary supplements derived from plants have accelerated in recent years. Ethnopharmacologists, botanists, microbiologists, and natural-products chemists are combing the Earth for phytochemicals and “leads” which could be developed for treatment of infectious diseases. While 25 to 50% of current pharmaceuticals are derived from plants, none are used as antimicrobials. Traditional healers have long used plants to prevent or cure infectious conditions; Western medicine is trying to duplicate their successes. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. This review attempts to summarize the current status of botanical screening efforts, as well as in vivo studies of their effectiveness and toxicity. The structure and antimicrobial properties of phytochemicals are also addressed. Since many of these compounds are currently available as unregulated botanical preparations and their use by the public is increasing rapidly, clinicians need to consider the consequences of patients self-medicating with these preparations.

Diet rapidly and reproducibly alters the human gut microbiome

Abstract: Long-term dietary intake influences the structure and activity of the trillions of microorganisms residing in the human gut, but it remains unclear how rapidly and reproducibly the human gut microbiome responds to short-term macronutrient change. Here we show that the short-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression. The animal-based diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale and Ruminococcus bromii). Microbial activity mirrored differences between herbivorous and carnivorous mammals, reflecting trade-offs between carbohydrate and protein fermentation. Foodborne microbes from both diets transiently colonized the gut, including bacteria, fungi and even viruses. Finally, increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat, bile acids and the outgrowth of microorganisms capable of triggering inflammatory bowel disease. In concert, these results demonstrate that the gut microbiome can rapidly respond to altered diet, potentially facilitating the diversity of human dietary lifestyles.

A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol.

Abstract: Aims: The minimum inhibitory concentration (MIC) of oregano essential oil (OEO) and two of its principle components, i.e. thymol and carvacrol, against Pseudomonas aeruginosa and Staphylococcus aureus was assessed by using an innovative technique. The mechanism of action of the above substances was also investigated. Methods and Results: The applied technique uses 100-well microtitre plate and collects turbidimetric growth data. To produce the inhibition profiles, a wide range of concentrations were tested for each of the three compounds, as well as for carvacrol‐thymol mixtures. Following a specific mathematical analysis of the observed inhibition profiles from all compounds, it was suggested that mixtures of carvacrol and thymol gave an additive effect and that the overall inhibition by OEO can be attributed mainly to the additive antimicrobial action of these two compounds. Addition of low amounts of each additive: (a) increased permeability of cells to the nuclear stain EB, (b) dissipated pH gradients as indicated by the CFDA-SE fluorescent probe irrespective of glucose availability and (c) caused leakage of inorganic ions. Conclusions: Mixing carvacrol and thymol at proper amounts may exert the total inhibition that is evident by oregano essential oil. Such inhibition is due to damage in membrane integrity, which further affects pH homeostasis and equilibrium of inorganic ions. Significance and Impact of the Study: The knowledge of extent and mode of inhibition of specific compounds, which are present in plant extracts, may contribute to the successful application of such natural preservatives in foods, since certain combinations of carvacrol‐ thymol provide as high inhibition as oregano essential oil with a smaller flavour impact.