Current and emerging molecular diagnostic technologies applicable to bacterial food safety

There is an increasing need for rapid test methods to certify the quality and safety of food products. Current tests applied for the microbiological assessment of food products are based on standard approved culture-based isolation methods and can take several days to yield results. Nucleic acid diagnostic (NAD) tests for the identification of bacterial foodborne pathogens employing in vitro amplification technologies are capable of sensitive and specific detection of single or multiple pathogens in foods in a shorter timeframe than traditional methods. New developments in molecular biosensors have the potential to provide at-line bioanalysis, whereas microarray-based technologies may in the future be the NAD platforms of choice for multiple pathogen detection and identification. This article reviews current and emerging NAD platforms for foodborne bacterial pathogens that have the potential to impact food safety.     

Screening Test for Histamine in Fish

A rapid screening method is described that can detect histamine in fish. The method uses a two–step sequential enzyme system. First, diamine oxidase catalyzes the breakdown of histamine with formation of hydrogen peroxide. Hydrogen peroxide is then detected by formation of crystal violet from the leuco base in the presence of peroxidase. The two reactions can be combined and peroxidase can be used to control the tightness of the screening. The method can be used for raw or heat-processed fish.     

BIOACTIVE POLAR LIPIDS IN OLIVE OIL, POMACE AND WASTE BYPRODUCTS

Olive oil protects against atherosclerosis because of biologically active microconstituents. In this study, total polar lipids from olive oil, pomace, pomace oil and waste byproducts were extracted, fractionated by thin layer chromatography and tested for their bioactivity. The most active ones were further purified on high-performance liquid chromatography, and the resulting lipid fractions were tested for their bioactivity. Bioactive compounds were determined in all samples with the exception of olive pomace oil. These lipids inhibited platelet-activating factor (PAF)-induced platelet aggregation and also induced platelet aggregation. The bioactive compound from olive pomace has been chemically characterized as a glycerylether-sn-2-acetyl glycolipid based on mass spectra. Chemical determinations and mass spectrometry data reinforce the assumption that these active microconstituents share both similar bioactivity and common structural features. The existence of PAF antagonists in polar lipid extracts from olive oil waste by-products render them biologically valuable materials for the food industry that could be used for the production of functional foods.

PRACTICAL APPLICATIONS

Isolated bioactive polar lipids from waste by-products of the olive oil industry that act as inhibitors of platelet-activating factor (PAF) may be used for enrichment and production of foods with higher nutritional value, as PAF plays a major role in inflammatory disorders, including atherosclerosis development.     

EVIDENCE FOR AN ISOBUTYLAMIDE ASSOCIATED WITH HOST-PLANT RESISTANCE TO WESTERN FLOWER THRIPS, <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis>, IN CHRYSANTHEMUM

Bioassay-directed fractionation of extracts of chrysanthemum leaves using a choice test permitted isolation of a fraction that exhibited repellent activity against the western flower thrips (WFT). Analysis of this fraction from cultivars exhibiting varying degrees of host-plant resistance to WFT by high performance liquid chromatography revealed a distinctive peak, the height of which correlated with the degree of resistance of those cultivars to WFT. The peak was attributed to a novel unsaturated isobutylamide, N-isobutyl-(E, E, E, Z)-2,4,10,12-tetradecatetraen-8-ynamide.     

Factors affecting the adsorption of Lactobacillus plantarum bacteriocin bacST8KF to Enterococcus faecalis and Listeria innocua

Bacteriocin ST8KF (bacST8KF), produced by Lactobacillus plantarum ST8KF isolated from kefir, inhibits the growth of Enterococcus faecalis E88, Lactobacillus casei LHS, Lactobacillus curvatus DF38, Lactobacillus sakei DSM 20017^T, Lactobacillus salivarius 241 and Listeria innocua LMG 13568. Eighty per cent of bacST8KF adsorbed to La. casei LHS and La. sakei DSM 20017^T. However, the same level of adsorption was recorded to bacST8KF-resistant Lactobacillus paraplantarum ATCC 700211^T and Streptococcus caprinus ATCC 700066, suggesting that adherence to the cell surface occurs at random and not always at specific receptor sites. Adsorption of bacST8KF is affected by inorganic salts, acids, surfactants, alcohols, temperature and pH, as observed for E. faecalis E88 and Li. innocua LMG 13568. The target of bacST8KF is the cytoplasmic membrane, as indicated by changes in cell morphology and leakage of DNA and β-galactosidase from cells of E. faecalis E88 and Li. innocua LMG 13568 treated with bacST8KF. However, the mode of activity against E. faecalis E88 and Li. innocua LMG 13568 is bacteriostatic, as concluded from slight increases in optical density levels after a few hours in the presence of bacST8KF. Activity of bacST8KF doubled (from 12 800 AU mL⁻¹ to 25 600 AU mL⁻¹) when strain ST8KF was grown in the presence of Li. innocua LMG 13568, which may indicate some sort of quorum sensing.