agar and carvacrol

The aim of this study was to evaluate the antibiotic susceptibility of Listeria innocua (L. innocua) and Listeria monocytogenes (L. monocytogenes) cells in the presence of citral and carvacrol at sublethal concentrations in an agar medium. The presence of terpenes in the L. monocytogenes and L. innocua culture medium provided a reduction in the minimal inhibitory concentration (MIC) of all the antibiotics tested. These effects were dependent on the concentration of terpenes present in the culture medium. The combination of citral and carvacrol potentiated antibiotic activity by reducing the MIC values of bacitracin and colistin from 32.0 and 128.0 μg ml⁻¹ to 1.0 and 2.0 μg ml⁻¹, respectively. Thus, both Listeria species became more susceptible to these drugs. In this way, the colistin and bacitracin resistance of L. monocytogenes and L. innocua was reversed in the presence of terpenes. Results obtained in this study show that the phytochemicals citral and carvacrol potentiate antibiotic activity, reducing the MIC values of cultured L. monocytogenes and L. innocua.. Phytochemicals citral and carvacrol potentiate antibiotic activity of erythromycin, bacitracin and colistin by reducing the MIC values of cultured Listeria monocytogenes and Listeria innocua. This effect in reducing the MIC values of the antibiotics tested in both micro-organisms was increased when natural antimicrobials were combined. This finding indicated that the combination among terpenes and antibiotic may contribute in reducing the required dosage of antibiotics due to the possible effect of terpenes on permeation barrier of the micro-organism cell membrane.

Topics: Acyclic Monoterpenes; Agar; Anti-Bacterial Agents; Bacitracin; Colistin; Cymenes; Drug Resistance, Bacterial; Listeria; Listeria monocytogenes; Microbial Sensitivity Tests; Monoterpenes

Carvacrol is known to inhibit a number of food borne pathogens. The activity of carvacrol vapour was evaluated against S. enterica serotype Enteritidis on tryptone soya agar and on pieces of raw chicken. On agar, the size of the inhibition zone increased with decreasing volume of agar, increasing vapour exposure period, increasing temperature, increasing volume of carvacrol used and with decreasing bacterial density. Inhibition was equally effective under aerobic and anaerobic conditions. On chicken pieces (10 x 10 x 5 mm, UV-sterilized and inoculated with approx. 5 x 10(3) cfu) carvacrol vapour significantly reduced viable numbers of salmonellae at 4, 20 and 37 degrees C and all viable cells were eliminated by a minimum of 3 h at 37 degrees C (p<0.05). A minimum concentration of 20% carvacrol v/v in ethanol was required to achieve a significant reduction and from 40% v/v no viable cells were recovered (p<0.05). In conclusion, carvacrol vapour is effective at inhibiting the growth of S. enterica serotype Enteritidis on agar and at inhibiting and eliminating these bacteria on the surface of raw chicken.

Topics: Agar; Animals; Chickens; Colony Count, Microbial; Cymenes; Disinfectants; Dose-Response Relationship, Drug; Food Contamination; Food Handling; Humans; Microbial Viability; Monoterpenes; Salmonella enteritidis; Temperature; Time Factors; Volatilization

The major components of oregano and thyme essential oils that had previously been shown to inhibit Escherichia coli O157:H7 were determined by high-performance liquid chromatography with UV detection and liquid chromatographic tandem mass spectrometry. The MICs and MBCs of carvacrol, thymol, p-cymene, and gamma-terpinene against a strain of E. coli O157: H7 phage type 34 isolated from bovine feces were determined by microdilution assay. The constituents were then tested in checkerboard assays to detect possible interactions. Carvacrol and thymol displayed bacteriostatic and bactericidal properties with MICs of 1.2 mmol/liter and were additive in combination. p-Cymene and gamma-terpinene displayed no measurable antibacterial activity up to 50 mmol/liter, and neither influenced the activity of carvacrol or thymol. Growth curves in the presence of nonlethal concentrations of carvacrol with the addition of agar (0.05%, wt/vol) or carrageenan (0.125%, wt/vol) as stabilizer were produced by optical density measurement. The stabilizers agar and carrageenan both significantly improved the effectiveness of carvacrol in broth, possibly because of a delay in the separation of the hydrophobic substrate from the aqueous phase of the medium. When carvacrol was dissolved in ethanol before addition to broth, stabilizers were not needed. Carvacrol and thymol, particularly when used in combination with a stabilizer or in an ethanol solution, may be effective in reducing the number or preventing growth of E. coli O157:H7 in liquid foods.

Topics: Agar; Anti-Infective Agents, Local; Carrageenan; Chromatography, High Pressure Liquid; Colony Count, Microbial; Cymenes; Dose-Response Relationship, Drug; Escherichia coli O157; Gas Chromatography-Mass Spectrometry; Microbial Sensitivity Tests; Monoterpenes; Oils, Volatile; Thymol; Time Factors