Inhibition of Glucosyltransferase Activity and Glucan Production as an Antibiofilm Mechanism of Lemongrass Essential Oil against Escherichia coli O157:H7

The resistance of Escherichia coli O157:H7 to disinfection is associated with its ability to form biofilms, mainly constituted by glucans produced by glucosyltransferases. Citral and geraniol, terpenes found in the essential oil of Cymbopogon citratus (EO), have proven antibacterial activity against planktonic E. coli; however, no information was found about their efficacy and mode of action against E. coli biofilms. Therefore, the inhibitory effect of C. citratus EO, citral, and geraniol on glucans production and glucosyltransferase activity as anti-biofilm mechanism against E. coli was evaluated. EO, citral, and geraniol inhibited the planktonic growth of E. coli (minimal inhibitory concentration or MIC= 2.2, 1.0, and 3.0 mg/mL, respectively) and the bacterial adhesion (2.0, 2.0, and 4.0 mg/mL, respectively) on stainless steel. All compounds decreased the glucans production; citral and geraniol acted as uncompetitive inhibitors of glucosyltransferase activity (The half maximal inhibitory concentrations or IC₅₀ were 8.5 and 6.5 µM, respectively). The evidence collected by docking analysis indicated that both terpenes could interact with the helix finger of the glucosyltransferase responsible for the polymer production. In conclusion, C. citratus EO, citral, and geraniol inhibited glucosyltransferase activity, glucans production, and the consequent biofilm formation of E. coli O157:H7.

Combination of Cymbopogon citratus and Allium cepa essential oils increased antibacterial activity in leafy vegetables

BACKGROUND

Cymbopogon citratus and Allium cepa essential oils (EOs) are rich in terpenes and sulfur compounds respectively, both with antibacterial activity and different cell targets, supporting the idea that their combination can increase their efficacy.

RESULTS

Major constituents of C. citratus were geranial and neral, while A. cepa presented dipropyl disulfide and dipropyl trisulfide. Cymbopogon citratus and A. cepa EOs inhibited the in vitro growth of Escherichia coli O157:H7 (minimal inhibitory concentrations of 2.21 and 5.13 g L-1 respectively), Salmonella Choleraesuis (3.04 and 1.28 g L-1 ), Listeria monocytogenes (1.33 and 2.56 g L-1 ) and Staphylococcus aureus (0.44 and 5.26 g L-1 ). Application of the EO combination to spinach caused a greater reduction in E. coli (2.34 log colony-forming units (CFU) g-1 ), S. Choleraesuis (2.94 log CFU g-1 ), L. monocytogenes (2.06 log CFU g-1 ) and S. aureus (1.37 log CFU g-1 ) compared with higher doses of individual EOs; a similar effect was observed for romaine lettuce. Individual and combined EOs caused a reduction in flavor acceptability level; however, no significant differences were found among odor acceptability of control vegetables and those treated with the EO combination and C. citratus EO.

CONCLUSION

Leafy vegetables treated with the EO combination showed higher antibacterial protection and odor acceptability compared with individual EO treatments. © 2016 Society of Chemical Industry.

Oregano Essential Oil as an Antimicrobial and Antioxidant Additive in Food Products

Food consumers and industries urged the need of natural alternatives to assure food safety and quality. As a response, the use of natural compounds from herbs and spices is an alternative to synthetic additives associated with toxic problems. This review discusses the antimicrobial and antioxidant activity of oregano essential oil (OEO) and its potential as a food additive. Oregano is a plant that has been used as a food seasoning since ancient times. The common name of oregano is given to several species: Origanum (family: Lamiaceae) and Lippia (family: Verbenaceae), amongst others. The main compounds identified in the different OEOs are carvacrol and thymol, which are responsible for the characteristic odor, antimicrobial, and antioxidant activity; however, their content may vary according to the species, harvesting season, and geographical sources. These substances as antibacterial agents make the cell membrane permeable due to its impregnation in the hydrophobic domains, this effect is higher against gram positive bacteria. In addition, the OEO has antioxidant properties effective in retarding the process of lipid peroxidation in fatty foods, and scavenging free radicals. In this perspective, the present review analyzes and discusses the state of the art about the actual and potential uses of OEO as an antimicrobial and antioxidant food additives.

Oregano (Lippia graveolens) essential oil added within pectin edible coatings prevents fungal decay and increases the antioxidant capacity of treated tomatoes

BACKGROUND

Tomato is a fruit widely consumed due to its flavor and nutritional value; however, it is susceptible to fungi contamination. Oregano essential oil (OEO) is a fungicide whose constituents are volatile; therefore, their incorporation within edible coatings can protect them and maintain their efficacy. In this context, this study evaluated the effect of OEO applied within pectin coatings on the inhibition of Alternaria alternata growth, antioxidant content and sensorial acceptability of tomatoes.

RESULTS

The major volatile compounds of OEO were carvacrol (47.41%), p-cymene (26.44%) and thymol (3.02%). All the applied OEO concentrations (15.7, 25.9 and 36.1 g L(-1) ) inhibited the in vitro growth of A. alternata, whereas the in vivo effective concentrations were 25.9 and 36.1 g L(-1) . Additionally, there was an increment of total phenols and antioxidant activity in coated tomatoes compared to controls. Aroma acceptability of tomatoes was not affected by the pectin-OEO coating; additionally, the pectin, pectin-OEO 15.7 g L(-1) treatments and control tomatoes showed higher flavor acceptability than those coated with pectin-OEO 25.9 and 36.1 g L(-1) .

CONCLUSION

Pectin-OEO coatings showed antifungal effect and increased the antioxidant activity without negative effects on the sensorial acceptability of tomatoes. © 2015 Society of Chemical Industry.

Oregano essential oil-pectin edible films as anti-quorum sensing and food antimicrobial agents

Edible films can be used as carriers for antimicrobial compounds to assure food safety and quality; in addition, pathogenesis of food bacteria is related to a cell to cell communication mechanism called quorum sensing (QS). Oregano essential oil (OEO) has proved to be useful as food antimicrobial; however, its food applications can be compromised by the volatile character of its active constituents. Therefore, formulation of edible films containing OEO can be an alternative to improve its food usages. QS inhibitory activity of OEO and pectin-OEO films was evaluated using Chromobacterium violaceum as bacterial model. Additionally, antibacterial activity was tested against Escherichia coli O157:H7, Salmonella Choleraesuis, Staphylococcus aureus, and Listeria monocytogenes. OEO was effective to inhibit bacterial growth at MIC of 0.24 mg/mL for all tested bacteria and MBC of 0.24, 0.24, 0.48, and 0.24 mg/mL against E. coli O157:H7, S. Choleraesuis, S. aureus, and L. monocytogenes, respectively. Pectin-films incorporated with 36.1 and 25.9 mg/mL of OEO showed inhibition diameters of 16.3 and 15.2 mm for E. coli O157:H7; 18.1 and 24.2 mm for S. Choleraesuis; 20.8 and 20.3 mm for S. aureus; 21.3 and 19.3 mm for L. monocytogenes, respectively. Pectin-OEO film (15.7 mg/mL) was effective against E. coli O157:H7 (9.3 mm), S. aureus (9.7 mm), and L. monocytogenes (9.2 mm), but not for S. Choleraesuis. All concentrations of OEO (0.0156, 0.0312, 0.0625 and 0.125 mg/mL) and pectin-OEO films (15.7, 25.9 and 36.1 mg/mL) showed a significant anti-QS activity expressed as inhibition of violacein production by C. violaceum. Additionally, the application of pectin-OEO films was effective reducing total coliforms, yeast, and molds of shrimp and cucumber slices stored at 4°C during 15 d. These results demonstrated the potential of pectin films enriched with OEO as food related microorganisms and QS inhibitors.