Influence of diluent on antimicrobial activity of cinnamon bark essential oil vapor against Staphylococcus aureus and Salmonella enterica on a laboratory medium and beef jerky.

The influence of chemical diluents on the antimicrobial activity of plant essential oil (EO) vapors was evaluated. We first determined if vapors generated from 22 chemical diluents not containing EO had antimicrobial activities. Ethyl ether vapor retarded the growth of S. aureus. The minimal inhibitory concentrations (MICs) and the minimal lethal concentrations (MLCs) of cinnamon bark EO vapor, which was diluted in and generated from 21 diluents, against S. aureus and S. enterica were determined. Cinnamon bark EO vapor showed significantly (P ≤ 0.05) lower MICs against S. aureus when diluted in dimethyl sulfoxide (DMSO), ethanol, ethyl acetate, or jojoba oil, and against S. enterica when diluted in DMSO, ethanol, or jojoba oil, compared to those in other diluents. We compared antimicrobial activities of cinnamon bark EO vapor diluted in DMSO, ethanol, ethyl acetate, or jojoba oil against S. aureus and S. enterica on beef jerky as a food model. Antimicrobial activity was significantly (P ≤ 0.05) higher when vaporized from DMSO. These results indicate that antimicrobial activity of cinnamon bark EO vapor may vary significantly (P ≤ 0.05) depending on the type of diluent from which it is vaporized. These observations provide basic information when developing food and food-contact surface decontamination strategies using EO vapors.

Effects of temperature, pH and sodium chloride on antimicrobial activity of magnesium oxide nanoparticles against E. coli O157:H7.

AIM: This study was done to determine the effects of temperature, pH and sodium chloride (NaCl) on antimicrobial activity of magnesium oxide (MgO) nanoparticles (NPs) against E. coli O157:H7. METHODS AND RESULTS: Culture conditions were established by varying the pH (5.0, 7.2 and 9.0), NaCl concentration (0.5, 2.0, 3.5 and 5.0%, w/v), and incubation temperatures (4, 12, 22 and 37°C). At each condition, the antimicrobial activities of MgO-NPs (0, 1, 2 and 4 mg/ml) against E. coli O157:H7 were measured. Four-way analysis of variance indicated interactions among all factors had a significant effect (p ≤ 0.05) on the antimicrobial activity of MgO-NPs. The concentration of MgO-NPs necessary to cause a 5-log reduction of E. coli O157:H7 under the most inhibitory conditions (37°C, pH 9.0, and 5.0% NaCl) was 0.50 mg/ml of MgO-NPs. CONCLUSION: The antimicrobial activity of the MgO-NPs increased significantly (p ≤ 0.05) with increased temperature, pH and NaCl concentration in TSB. SIGNIFICANCE AND IMPACT OF THE STUDY: The influence of intrinsic and extrinsic factors on antimicrobial activity of MgO-NPs we found will contribute to the development of microbial decontamination strategies using MgO in the food industry.

Inactivation of Escherichia coli O157:H7 on radish and cabbage seeds by combined treatments with gaseous chlorine dioxide and heat at high relative humidity.

This study was done to develop a method to inactivate Escherichia coli O157:H7 on radish and cabbage seeds using simultaneous treatments with gaseous chlorine dioxide (ClO2) and heat at high relative humidity (RH) without decreasing seeds' viability. Gaseous ClO2 was spontaneously vaporized from a solution containing hydrochloric acid (HCl, 1 N) and sodium chlorite (NaClO2, 100,000 ppm). Using a sealed container (1.8 L), an equation (y = 5687×, R2 = 0.9948) based on the amount of gaseous ClO2 generated from HCl-NaClO2 solution at 60 °C and 85% RH was developed. When radish or cabbage seeds were exposed to gaseous ClO2 at concentrations up to 3,000 ppm for 120 min, germination rates did not significantly decrease (P > 0.05). When seeds inoculated with E. coli O157:H7 were treated with 2,000 or 3,000 ppm of gaseous ClO2 in an atmosphere with 85% RH at 60 °C, populations (6.8-6.9 log CFU/g) on both types of seeds were decreased to below the detection limit for enrichment (-0.5 log CFU/g) within 90 min. This study provides useful information for developing a decontamination method to control E. coli O157:H7 and perhaps other foodborne pathogens on plant seeds by simultaneous treatment with gaseous ClO2 and heat at high RH.