Antimicrobial Effects of Nisin, Essential Oil, and γ-Irradiation Treatments against High Load of Salmonella typhimurium on Mini-carrots

Changes in inoculated Salmonella enterica subsp. enterica Serovar Enteritidis and other microbiological qualities of vacuum-packed carrot slices after treatment with aqueous extract of Lobularia maritima

After harvesting, pathogens can infect fresh vegetables in different ways. Pathogenic bacteria associated with fresh vegetables can cause widespread epidemics associated with foodborne illness. The aim of this study was to assess the microbiological quality of carrot slices after treatment with aqueous extracts of Lobularia maritima (AELm) at different concentrations AELm1 (10 mg/mL), AELm2 (5 mg/mL), AELm3 (2.5 mg/mL) and AELm4 (1.25 mg/mL), and Salmonella enterica subsp. enterica serovar Enteritidis, along with vacuum packaging and storage of carrots for 7 days at 4 °C. On days 1. and 7., total viable counts (TVC), and coliforms bacteria (CB), and Salmonella count were all analysed. Microorganisms that were obtained from carrots were identified using MALDI-TOF MS Biotyper Mass Spectrometry. The total viable, coliform bacteria and Salmonella counts were varied by the group of treatment. Higher counts were found in the control group on both days. The most isolated species of bacteria were Salmonella enterica and Pantoea agglomerans on the 1. day and Klebsiella oxytoca on the 7. day. The current study adds useful information for a better understanding of how Salmonella enterica reacts to the effect of AELm and its potential use as a sustainable washing method to eliminate bacteria from freshly cut carrots.

Effect of Gamma Irradiation on Pathogenic Staphylococcus aureus in Packaged Ready-to-Eat Salads Treated with Biological Extracts

Providing pathogen-free ready-to-eat (RTE) salads is critical for all consumers, especially individuals with weakened immunity. In this study, the efficacy of γ-irradiation on Staphylococcus aureus (S. aureus) in freshly packaged salads (4.24 log CFU/g) treated with essential oil (EO) and myrtle juice during 10 days of storage and their impact on organoleptic properties were investigated. EO was extracted by hydrodistillation and the chemical composition was analyzed by gas chromatography with Flame Ionization Detector (GC/FID) and gas chromatography/mass spectrometry (GC/MS). Myrtle juice was prepared from fresh fruits. The cytotoxic effects of Thymus capitatus (T. capitatus) EO against a normal human umbilical vein endothelial cell (HUVEC) were assessed. GC/FID and GC-MS analysis of the thyme EO revealed the presence of 13 compounds, including carvacrol (79.55%) and p-cymene (7.93%) as major components. The EO was found to be noncytotoxic, with concentrations lower than 0.16 µL/mL. A reduction of more than 3 log CFU/g and a total inactivation of S. aureus were achieved with the combination of gamma irradiation at 0.5 kGy with myrtle juice at 6 µL/mL and EO at 0.08 µL/mL, respectively. The treatment of fresh RTE salads with thyme and myrtle juice was evaluated as acceptable by the sensory panel. The combined effect showed a synergistic potential on the inactivation of S. aureus.

Essential Oils with High Activity against Stationary Phase Bartonella henselae

Bartonella henselae is a fastidious Gram-negative intracellular bacterium that can cause cat scratch disease, endocarditis in humans and animals, as well as other complications, leading to acute or chronic infections. The current treatment for Bartonella infections is not very effective due to antibiotic resistance and also persistence. To develop better therapies for persistent and chronic Bartonella infections, in this study, with the help of SYBR Green I/PI viability assay, we performed a high-throughput screening of an essential oil library against the stationary phase B. henselae. We successfully identified 32 essential oils that had high activity, including four essential oils extracted from Citrus plants, three from Origanum, three from Cinnamomum, two from Pelargonium, and two from Melaleuca, as well as frankincense, ylang-ylang, fir needle, mountain savory (winter), citronella, spearmint, elemi, vetiver, clove bud, allspice, and cedarwood essential oils. The minimal inhibitory concentration (MIC) determination of these 32 top hits indicated they were not only active against stationary phase non-growing B. henselae but also had good activity against log-phase growing B. henselae. The time-kill assay showed 13 active hits, including essential oils of oregano, cinnamon bark, mountain savory (winter), cinnamon leaf, geranium, clove bud, allspice, geranium bourbon, ylang-ylang, citronella, elemi, and vetiver, could eradicate all stationary phase B. henselae cells within seven days at the concentration of 0.032% (v/v). Two active ingredients, carvacrol and cinnamaldehyde, of oregano and cinnamon bark essential oils, respectively, were shown to be very active against the stationary phase B. henselae such that they were able to eradicate all the bacterial cells even at the concentration ≤ 0.01% (v/v). More studies are needed to identify the active components of some potent essential oils, decode their antimicrobial mechanisms, and evaluate their activity against Bartonella infections in animal models.

Antimicrobial effect and mechanism of cinnamon oil and gamma radiation on Shewanella putrefaciens

The aims of this study were to observe the antimicrobial effect and mechanism of cinnamon oil combined with gamma radiation on Shewanella putrefaciens. Gamma radiation increased the antimicrobial activity of cinnamon oil, and the relative radiation sensitivity of gamma radiation on S. putrefaciens was increased by cinnamon oil. Gamma radiation significantly increased the changes of bacterial morphology, intra-adenosine 5'-triphosphate (intra-ATP) and extra-ATP concentrations and pH_in value of S. putrefaciens treated cinnamon oil. Although, gamma radiation used alone didn't damage the bacterial morphology and ATP concentrations significantly. Gamma radiation assisted cinnamon oil to damage the cell permeability and integrity of S. putrefaciens, thus the combination of cinnamon oil and gamma radiation showed a better antimicrobial activity than used alone.