Antibacterial effect and mechanisms of action of 460-470 nm light-emitting diode against Listeria monocytogenes and Pseudomonas fluorescens on the surface of packaged sliced cheese.

The aim of this study was to investigate the antibacterial effect of 460-470 nm light-emitting diode (LED460-470nm) illumination against pathogens and spoilage bacteria on the surface of agar media and packaged sliced cheese. LED460-470nm illumination highly inhibited the growth of Listeria monocytogenes and Pseudomonas fluorescens on agar media covered with oriented polypropylene (OPP) film (thickness, 0.03 mm). When sliced cheeses inoculated with L. monocytogenes or P. fluorescens and packaged with OPP film were illuminated by an LED460-470 nm at 4 or 25 °C, reduction levels of L. monocytogenes and P. fluorescens on packaged slice cheese were higher at 4 °C than at 25 °C. There were no significant differences in color between non-illuminated and illuminated sliced cheese after storage for 7 d at 4 °C. LED460-470 nm illumination at 4 °C for 4 d caused cellular injury of L. monocytogenes and P. fluorescens related to RNA, protein, and peptidoglycan metabolism, and a disruption of the cell membrane and loss of cytoplasmic components were observed from TEM results. These results suggest that LED460-470 nm illumination, in combination with refrigeration temperatures, may be applied to extend the shelf-life of packaged slice cheese and minimize the risk of foodborne disease, without causing color deterioration.

Effects of sterilization methods on the survival of pathogenic bacteria in potting soil stored at various temperatures.

Fresh food products can be contaminated with pathogenic bacteria in various agricultural environments. Potting soil is sterilized by heat sterilization and then reused. This study evaluated the effects of three sterilization methods (non-sterilized, pasteurized, and sterilized) on the survival of pathogenic bacteria in potting soil during storage for 60 days at 5, 15, 25, and 35 °C. The reduction in Escherichia coli O157:H7, Salmonella Typhimurium, and Staphylococcus aureus in potting soil was higher at higher temperatures (25 and 35 °C) than at lower temperatures (5 and 15 °C). The population of pathogenic bacteria in pasteurized and sterilized potting soil was reduced below the detectable levels within 30 days at 35 °C. In contrast, the population of Bacillus cereus did not change in potting soil during storage for 60 days at all temperatures. These results indicate that sterilization and storage temperature of potting soil are critical factors influencing the survival of pathogenic bacteria.

Comparison of measurement methods at determining the target sites injured by antimicrobials in Escherichia coli O157:H7 using metabolic inhibitors.

Acquiring an understanding of the mechanisms underlying antimicrobial action is important for overcoming bacterial resistance to antimicrobials. This study evaluated three different methods (antimicrobial fixed broth dilution method, metabolic inhibitors fixed broth dilution method, and metabolic inhibitor fixed agar recovery method) for determining the target site of Escherichia coli O157:H7 by treatments with various antimicrobials (ethanol, ethylenediaminetetraacetic acid, polymyxin B, thymol, acetic acid, and citrus fruit extract). However, the results indicated only weak relationships between MIC values and mechanisms of antimicrobials known to cause damage or injury. In addition, the results of three measurement methods using metabolic inhibitors were not correlated. These results suggest that measurement methods using metabolic inhibitors alone may not be suitable for determining the target site injured by antimicrobials. Therefore, various measurement methods should be compared and analyzed to determine the damage or injury sites targeted by antimicrobials in pathogenic bacteria. Further studies are needed to compare and analyze the various measurement methods for determining the target site injured by antimicrobials in pathogenic bacteria.

Development of Strategies to Minimize the Risk of Listeria monocytogenes Contamination in Radish, Oriental Melon, and Carrots.

Contamination by Listeria monocytogenes in packaged produce is a major concern. The purpose of this study was to find natural and affordable sanitizers to reduce L. monocytogenes contamination in agricultural products. Organic acids, ultraviolet-C (UV-C), and ethanol were analyzed either alone or in combination to assess their ability to reduce L. monocytogenes population in radish, oriental melon, and carrot samples. In radish samples, 3% malic acid combined with UV-C at a dosage of 144 mj/cm2 significantly reduced (>4 log CFU/g) the population of L. monocytogenes (1.44 ± 0.5) compared to the control sample (5.14 ± 0.09). In the case of the melon samples, exposure to UV-C at a dosage of 144 mj/cm2 combined with 3% lactic acid (2.73 ± 0.75) or 50% ethanol (2.30 ± 0.01) was effective against L. monocytogenes compared to the control sample (5.10 ± 0.19). In carrot samples, 3% lactic acid combined with 144 mj/cm2 dosage UV-C reduced L. monocytogenes population (4.48 ± 0.25) more than in the control sample (5.85 ± 0.08). These results reveal that sanitizers that are effective for one crop are less effective for another crop indicating that effective prevention methods should be customized for each crop to prevent pathogen cross contamination during postharvest washing.

Synergistic effects of blue light-emitting diodes in combination with antimicrobials against Escherichia coli O157:H7 and their mode of action.

This study was conducted to evaluate the antibacterial effect of 460-470 nm light-emitting diodes illumination (460/470 LED) combined with various antimicrobials at inactivating Escherichia coli O157:H7 and identify the antibacterial mechanisms. When carvacrol, thymol, citric acid, malic acid, citrus fruit extract, 3% NaCl, or 5% NaCl was combined with 460/470 LED, there was a higher reduction in E. coli O157:H7 compared to 460/470 LED treatment or antimicrobials alone at 4 °C. Particularly, a marked synergistic effect (>8.74 log10 CFU/ml) was observed when 460/470 LED was combined with carvacrol, malic acid, citrus fruit extract, or 3% NaCl. Levels of intracellular ROS and lipid peroxidation of E. coli O157:H7 were higher in the combination of 460/470 LED and antimicrobials compared to individual treatments. Moreover, the combination treatment increased depolarization of the cell membrane leading to membrane damage as well as the loss of DNA integrity. Thus, adding antimicrobial treatment to 460/470 LED could improve its efficacy against pathogenic bacteria such as E. coli O157:H7.

Evaluation of the microbial contamination of fresh produces and their cultivation environments from farms in Korea.

In this study, a total of 195 samples including fresh produce and farming environments was used to perform the microbial risk assessment. Levels of total aerobic bacteria ranged from 2.77 to 5.99, 6.28 to 7.81, and 1.31 to 2.74 log10 CFU/g, whereas levels of coliforms were ≤ 2.48, ≤ 3.35, and ≤ 0.85 log10 CFU/g, levels of Escherichia coli were ≤ 1.04, ≤ 0.12, and ≤ 1.69 log10 CFU/g in fresh produce, soil, and irrigation water, respectively. When the presence of pathogenic bacteria was detected, only Bacillus cereus and Staphylococcus aureus were isolated from 14 (7.2%) and 7 (3.6%) samples out of 195 samples, respectively. From the results, it was difficult to find a strong correlation between microbial contamination of fresh produce and their farming environments. However, continuous monitoring of agricultural products and related environments should be undertaken in order to ensure the microbial safety of fresh produce.

Evaluation of the microbiological quality of jacopevers and plaices in Korea, 2015-2016.

In Southeast Asian countries, including Korea, China, and Japan, the considerable amounts of raw fish have been annually consumed in the manner of live fish fillets without minimally thermal processing, increasing the risks of causing food-borne diseases. This study investigated the occurrence of total aerobic bacteria (TAB), coliform, Vibrio parahaemolyticus, Salmonella enterica serovar spp., Listeria monocytogenes, and Staphylococcus aureus in jacopevers and plaices. Total 200 live fishes were collected from randomly selected restaurants located in Anseong-si, and then they were microbiologically monitored. TAB ranged from 3.09 to 3.21 Log10 CFU/g in jacopever and plaice. Coliform in the levels of 1.54 Log10 CFU/g were detected in samples. Out of 100 jacopevers, a single jacopever (1%) exhibited the prevalence of S. aureus in the edible part, though none of pathogenic bacteria were detected. These results will be useful for understanding the microbial prevalence in the domestic living jacopevers and plaices.

Combined Application of Antibrowning, Heat Treatment and Modified-Atmosphere Packaging to Extend the Shelf Life of Fresh-Cut Lotus Root.

This work aimed to determine the effects of different concentrations of antibrowning treatments (that is, distilled water [DW], 1% ascorbic acid [AA], 0.5% chamomile [CM], and 1% AA + 0.5% CM) and heat-treatment (55 °C for 45 s) combined with packaging under 4 different modified-atmosphere gas compositions (that is, air, vacuum, 100% CO2 , 50% CO2 /50% N2 ) on the quality and microbiological characteristics of fresh-cut lotus root. The quality characteristics (that is, color, weight loss, texture, pH, polyphenoloxidase activity, and total phenolic content) of the AA + CM-dipped sample in 100% CO2 packaging were maintained significantly better than those of the other samples (P < 0.05). The microbiological counts observed in the DW-dipped sample during storage were higher than those of the AA, CM, and AA + CM samples, and heat-treatment retarded the microbiological deterioration of fresh-cut lotus root. Therefore, the results revealed that dipping in an antibrowning treatment (AA + CM), and 100% CO2 MAP with heat treatment effectively extend the shelf life of fresh-cut lotus root to 21 d at 5 °C.

Growth characteristics and biofilm formation of various spoilage bacteria isolated from fresh produce.

UNLABELLED: This study investigated the characteristics of spoilage bacteria isolated from fresh produce including growth at various temperatures, biofilm formation, cell hydrophobicity, and colony spreading. The number of spoilage bacteria present when stored at 35 °C was significantly greater than when stored at lower temperatures, and maximum population size was achieved after 10 h. However, Bacillus pumilus, Dickeya zeae, Pectobacterium carotovorum subsp. Carotovorum Pcc21, and Bacillus pumilus (RDA-R) did not grow at the storage temperature of 5 °C. The biofilm formation by Clavibacter michiganensis, Acinetobacter calcoaceticus, and A. calcoaceticus (RDA-R) are higher than other spoilage bacteria. Biofilm formation showed low correlation between hydrophobicity, and no significant correlation with colony spreading. These results might be used for developing safe storage guidelines for fresh produce at various storage temperatures, and could be basic information on the growth characteristics and biofilm formation properties of spoilage bacteria from fresh produce. PRACTICAL APPLICATION: Growth of spoilage bacteria was different depending on the bacteria strains and storage temperature. Between biofilm formation and cell hydrophobicity was low correlation on spoilage bacteria. Therefore, growth characteristics and biofilm formation of spoilage bacteria might be used for developing safe storage guidelines for fresh produce at various storage temperatures.