Oregano Essential Oil versus Conventional Disinfectants against Salmonella Typhimurium and Escherichia coli O157:H7 Biofilms and Damage to Stainless-Steel Surfaces.

This study compared the effect of oregano essential oil versus sodium hypochlorite, hydrogen peroxide, and benzalkonium chloride against the viability of adhered Salmonella Typhimurium and Escherichia coli O157:H7 on 304 stainless steel. Oregano essential oil was effective in disrupting the biofilms of both bacteria at concentrations ranging from 0.15 to 0.52 mg mL-1. In addition, damage to stainless-steel surfaces following disinfection treatments was assessed by weight loss analysis and via visual inspection using light microscopy. Compared to the other treatments, oregano oil caused the least damage to stainless steel (~0.001% weight loss), whereas sodium hypochlorite caused the most severe damage (0.00817% weight loss) when applied at 0.5 mg mL-1. Moreover, oregano oil also had an apparent protective impact on the stainless steel as weight losses were less than for the control surfaces (distilled water only). On the other hand, sodium hypochlorite caused the most severe damage to stainless steel (0.00817% weight loss). In conclusion, oregano oil eliminated monoculture biofilms of two important foodborne pathogens on 304 stainless-steel surfaces, while at the same time minimizing damage to the surfaces compared with conventional disinfectant treatments.

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.

Synergistic mode of action of catechin, vanillic and protocatechuic acids to inhibit the adhesion of uropathogenic Escherichia coli on silicone surfaces.

AIMS: To study the individual and combined contribution of catechin, protocatechuic and vanillic acids to inhibit the adhesion of uropathogenic Escherichia coli (UPEC) on the surface of silicone catheters. METHODS AND RESULTS: The adhesion of UPEC to silicone catheters during the exposure to nonlethal concentrations of phenolic compounds was measured, as well as changes in motility, presence of fimbriae, extra-cellular polymeric substances, surface charge, hydrophobicity and membrane fluidity. The phenolic combination reduced 26-51% of motility, 1 log CFU per cm2 of adhered bacteria and 20-40% the carbohydrate and protein content in the biofilm matrix. Curli fimbriae, surface charge and cell hydrophobicity were affected to a greater extent by the phenolic combination. In the mixture, vanillic acid was the most effective for reducing bacterial adhesion, extra-polymeric substance production, motility, curli fimbriae and biofilm structure. Notwithstanding, protocatechuic acid caused major changes in the bacterial cell surface properties, whereas catechin affected the cell membrane functionality. CONCLUSION: Catechin, protocatechuic and vanillic acids have different bacterial cell targets, explaining the synergistic effect of their combination against uropathogenic E. coli. SIGNIFICANCE AND IMPACT OF STUDY: This study shows the contribution of catechin, protocatechuic and vanillic acids in producing a synergistic mixture against the adhesion of uropathogenic E. coli on silicone catheters. The action of catechin, vanillic and protocatechuic acids included specific contributions of each compound against the E. coli membrane's integrity, motility, surface properties and production of extracellular polymeric substances. Therefore, the studied mixture of phenolic compounds could be used as an antibiotic alternative to reduce urinary tract infections associated with silicone catheters.

Virulence of Pseudomonas aeruginosa exposed to carvacrol: alterations of the Quorum sensing at enzymatic and gene levels.

The main goal of this study was to evaluate the inhibition of Pseudomonas aeruginosa virulence factors and Quorum Sensing during exposure to carvacrol. P. aeruginosa (ATCC 10154) was exposed to carvacrol determining changes in biofilm development, motility, acyl-homoserine lactones (AHL) synthesis and relative expression of lasI/lasR. Docking analysis was used to determinate interactions between carvacrol with LasI and LasR proteins. P. aeruginosa produced 60% lower AHLs when exposed to carvacrol (1.9 mM) compared to control, without affecting cellular viability, indicating a reduction on the LasI synthase activity. AHL-C12, C6, and C4 were detected and related to biofilm development, motility, and pyocyanin production, respectively. The presence of carvacrol reduced the expression of lasR, without affecting lasI gen. Moreover, computational docking showed interactions of carvacrol with amino acids in the active site pocket of LasI (-5.6 kcal mol-1) and within the binding pocket of LasR (-6.7 kcal mol-1) of P. aeruginosa. These results demonstrated that virulence of P. aeruginosa was reduced by carvacrol, by inhibiting LasI activity with the concomitant reduction on the expression of lasR, biofilm and swarming motility. This study provides relevant information about the effect of carvacrol against quorum sensing to inhibit virulence factors of P. aeruginosa at enzymatic and gene levels. These findings can contribute to the development of natural anti-QS products, which can affect pathogenesis.

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.