Green Fluorescent Protein Labeling of Listeria, Salmonella, and Escherichia coli O157:H7 for Safety-Related Studies

Many food safety-related studies require tracking of introduced foodborne pathogens to monitor their fate in complex environments. The green fluorescent protein (GFP) gene (gfp) provides an easily detectable phenotype so has been used to label many microorganisms for ecological studies. The objectives of this study were to label major foodborne pathogens and related bacteria, including Listeria monocytogenes, Listeria innocua, Salmonella, and Escherichia coli O157:H7 strains, with GFP and characterize the labeled strains for stability of the GFP plasmid and the plasmid's effect on bacterial growth. GFP plasmids were introduced into these strains by a CaCl2 procedure, conjugation or electroporation. Stability of the label was determined through sequential propagation of labeled strains in the absence of selective pressure, and rates of plasmid-loss were calculated. Stability of the GFP plasmid varied among the labeled species and strains, with the most stable GFP label observed in E. coli O157:H7. When grown in nonselective media for two consecutive subcultures (ca. 20 generations), the rates of plasmid loss among labeled E. coli O157:H7, Salmonella and Listeria strains ranged from 0%–30%, 15.8%–99.9% and 8.1%–93.4%, respectively. Complete loss (>99.99%) of the plasmid occurred in some labeled strains after five consecutive subcultures in the absence of selective pressure, whereas it remained stable in others. The GFP plasmid had an insignificant effect on growth of most labeled strains. E. coli O157:H7, Salmonella and Listeria strains can be effectively labeled with the GFP plasmid which can be stable in some isolates for many generations without adversely affecting growth rates

Does the use of ozonized water influence the chemical characteristics of organic cabbage (Brassica oleracea var. capitata)?

The aim of this study was to assess the influence of different cultivation procedures (conventional and organic), different sanitizers (ozone and chlorine) during the post-harvest storage of cabbages hybrid Fuyutoyo (Brassica oleracea var. capitata ). The cabbage plants were purchased directly from producers. At the end of the cropping cycle, which occurred 120 days after sowing, crop harvesting was carried out and the plants were immediately sanitized with water, chlorine and ozone. After cleansing, the cabbage plants were stored in a cooling chamber at 5 \ub0C between 12 and 20 days. To predict the effect of commercialization, the cabbage head were removed between 12 and 20 days from the cooling chamber, one part was analyzed and the rest maintained in a local temperature (22\ub12 \ub0C) for 4 days. The biochemical analysis of the following were determined: total phenols, total flavonoids, vitamin C, total chlorophyll, nitrate, polyamines and antioxidant activity after 0, 12 and 20 days storage and 4 days at room temperature (12+4 and 20+4 days of storage), for market analysis. The biochemical analyses showed no statistical differences between conventional and organic cabbages. Thus, the consumption of organic or conventional cabbage provide the same content of antioxidant compounds analyzed and the sanitizing procedure (ozonated water ) did not modify the antioxidant capacity of the plant