Development of a novel device for applying uniform doses of electron beam irradiation on carcasses

The Maxim's Electron Scatter Chamber (Maxim Chamber) was developed to obtain uniform dose distribution when applying electron beam (e-beam) irradiation to materials of irregular surface. This was achieved by placing a stainless steel mesh surrounding a cylindrical area where the target sample was placed. Upon contact with the mesh, electrons scatter and are directed onto the target from multiple angles, eliminating the e-beam linearity and resulting in a uniform dose distribution over the target surface. The effect of irradiation in the Maxim Chamber on dose distribution and pathogen reduction was tested on rabbit carcasses to simulate other larger carcasses. The dose uniformity ratio (DUR) on the rabbit carcasses was 1.8, indicating an acceptable dose distribution. On inoculated carcasses, this treatment reduced Escherichia coli O157:H7 by > 5 log cycles. These results indicate that carcass irradiation using e-beam is feasible using the Maxim's electron scattering chamber. Appropriate adjustments will be further needed for commercial application on beef and other animal carcasses.     

Use of linear, Weibull, and log-logistic functions to model pressure inactivation of seven foodborne pathogens in milk

Survival curves of six foodborne pathogens suspended in ultra high-temperature (UHT) whole milk and exposed to high hydrostatic pressure at 21.5 degrees C were obtained. Vibrio parahaemolyticus was treated at 300 MPa and other pathogens, Listeria monocytogenes, Escherichia coli O157:H7, Salmonella enterica serovar Enteritidis, Salmonella enterica serovar Typhimurium, and Staphylococcus aureus were treated at 600 MPa. All the survival curves showed a rapid initial drop in bacterial counts followed by tailing caused by a diminishing inactivation rate. A linear model and two nonlinear models were fitted to these data and the performances of these models were compared using mean square error (MSE) values. The log-logistic and Weibull models consistently produced better fits to the inactivation data than the linear model. The mean MSE value of the linear model was 6.1, while the mean MSE values were 0.7 for the Weibull model and 0.3 for the log-logistic model. There was no correlation between pressure resistance and the taxonomic group the bacteria belong to. The order, most to least pressure-sensitive, of the single strains tested was: V. parahaemolyticus (gram negative)相似文献   

ATP-regulation of antioxidant properties and phenolics in litchi fruit during browning and pathogen infection process

The impact of energy level on antioxidant properties in relation to pericarp browning and loss of disease resistance of litchi fruit was investigated. Litchi fruits were vacuum-infiltrated with distiled water (control), 1 mM adenosine triphosphate (ATP) and 0.5 mM 2,4-dinitrophenol (DNP) under 75 kPa for 3 min before being inoculated with Peronophythora litchi or not. ATP-treated fruits presented higher activities of antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX). Higher activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging, reducing power and contents of phenolic compounds were also observed in ATP-treated fruit during storage. In contrast, DNP treatment lowered the enzymes activities, scavenging ability and the contents of phenolic compounds. Higher levels of antioxidant enzymatic system and non-enzymatic system were observed in P. litchii-inoculated fruits than those in non-inoculated fruits. Application of ATP and DNP exhibited a similar change patterns and effects in inoculated fruits. When related to previously reported ATP levels, the results suggested that ATP levels could regulate the antioxidant system. Sufficient available energy is crucial for inhibiting browning and preventing the loss of disease resistance in harvested litchi fruit.     

Pyrosequencing of the 16S rRNA gene to reveal bacterial pathogen diversity in biosolids

Given the potential for a variety of bacterial pathogens to occur in variably stabilized sewage sludge (biosolids), an understanding of pathogen diversity and abundance is necessary for accurate assessment of infective risk when these products are land applied. 16S rDNA was PCR amplified from genomic DNA extracted from municipal wastewater residuals (mesophilic- and thermophilic-phased anaerobic digestion (MAD and TPAD), composting (COM)), and agricultural soil (SOIL), and these amplicons were sequenced using massively parallel pyrosequencing technology. Resulting libraries contained an average of 30,893 16S rDNA sequences per sample with an average length of 392 bases. FASTUNIFRAC-based comparisons of population phylogenetic distance demonstrated similarities between the populations of different treatment plants performing the same stabilization method (e.g. different MAD samples), and population differences among samples from different biosolids stabilization methods (COM, MAD, and TPAD). Based on a 0.03 Jukes-Cantor distance to 80 potential bacterial pathogens, all samples contained pathogens and enrichment ranged from 0.02% to 0.1% of sequences. Most (61%) species identified were opportunistic pathogens of the genera Clostridium and Mycobacterium. As risk sciences continue to evolve to address scenarios that include multiple pathogen exposure, the analysis described here can be used to determine the diversity of pathogens in an environmental sample. This work provides guidance for prioritizing subsequent culturable and quantitative analysis, and for the first time, ensuring that potentially significant pathogens are not left out of risk estimations.     

瓜类枯萎病菌生物学特性与药剂测定研究

对瓜类枯萎病的3种专化型即黄瓜专化型（F.oxysporum f.sp.cucumerinum)，西瓜专化型（F.oxysporum f.sp.niveum)和甜瓜专化型（F.oxysporm f.sp.melonis)进行了形态特点，生物学特性与药剂测定等室内比较研究。结果表明，枯萎病菌的3种专化型，在形态特征，培养性状以及对杀菌剂的敏感性等方面，既有明显的相似点，也有不同之处，菌丝生长的温度范围均为5-35℃，以25℃为最适；在20-30℃的温度范围内，孢子萌发率较高，病菌3种专化型的产孢量与温度的相关性不明显，pH值为6最适于孢子萌发，健根保，苗菌敌，无敌，根必治和重茬保5种药剂，对瓜类枯萎病菌菌丝生长的抑制效果较好。     

Detection probability of Campylobacter

A rapid presence/absence test for Campylobacter in chicken faeces is being evaluated to support the scheduling of highly contaminated broiler flocks as a measure to reduce public health risks [Nauta, M. J., & Havelaar, A. H. (2008). Risk-based standards for Campylobacter in the broiler meat chain. Food Control, 19, 372–381]. Although the presence/absence test is still under development, an example data set of test results is analysed to illustrate the benefit of the detection probability concept. The detection probability of Campylobacter increases with the logarithm of the Campylobacter concentration in faeces according to an S-shaped curve which stretches about 2–3 log units. The detection probability is 50% at a Campylobacter concentration of 7.4 × 10⁶ cfu/g. The uncertainty in the detection probability is 32% at the most for a 90% confidence interval. This type of information allows for realistic calculations on the Campylobacter status of different food processing paths after splitting. Usable quantitative estimates on detection probability await a data set of test results from a test that is ready for use or has similar properties.     

Automatic detection of Salmonella enterica in sprout irrigation water using a nucleic acid sensor

A nucleic acid sensor capable of automated sample and reagent loading, real-time PCR, automated detection, and sample line cleaning was tested. Real-time PCR reactions were performed with Salmonella enterica in autoclaved and spent alfalfa sprout irrigation water. S. enterica boiled cells were detected over a range of approximately 10⁴ to 10⁸ CFU/reaction (rxn). It was possible to generate enough PCR product to visualize a band on a gel at the expected size over approximately five orders of magnitude from 3.2 × 10³ to 10⁸ CFU/rxn. Automated detection experiments yielded correct identification of 9/9 positive control reactions over a range of 10⁴ to 10⁸ CFU/rxn, correctly identified a negative control reaction, and a sample of 3.2 × 10³ CFU/rxn was incorrectly identified as negative. Primer dimers were not seen in positive or negative control reactions with sprout irrigation water, suggesting that it may be possible to improve the detection limit simply by increasing the number of thermal cycles or by lowering the annealing temperature. The system required no interpretation of real-time PCR data by the operator. The entire process of loading, running the PCR, automated data interpretation, and sample line cleaning was completed in under 2 h and 20 min, significantly faster than it would take to ship a sample and have it tested by an independent laboratory.     

Macromolecule mediated transport and retention of Escherichia coli O157:H7 in saturated porous media

The role of extracellular macromolecules on Escherichia coli O157:H7 transport and retention was investigated in saturated porous media. To compare the relative transport and retention of E. coli cells that are macromolecule rich and deficient, macromolecules were partially cleaved using a proteolytic enzyme. Characterization of bacterial cell surfaces, cell aggregation, and experiments in a packed sand column were conducted over a range of ionic strength (IS). The results showed that macromolecule-related interactions contribute to retention of E. coli O157:H7 and are strongly linked to solution IS. Under low IS conditions (IS ≤ 0.1 mM), partial removal of the macromolecules resulted in a more negative electrophoretic mobility of cells and created more unfavorable conditions for cell-quartz and cell-cell interactions as suggested by Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profiles and cell aggregation kinetics. Consequently, less retention was observed for enzyme treated cells in the corresponding column experiments. In addition, a time-dependent deposition process (i.e., ripening) was observed for untreated cells, but not for treated cells, supporting the fact that the macromolecules enhanced cell-cell interactions. Additional column experiments for untreated cells under favorable conditions (IS ≥ 1 mM) showed that a significant amount of the cells were reversibly retained in the column, which contradicts predictions of DLVO theory. Furthermore, a non-monotonic cell retention profile was observed under favorable attachment conditions. These observations indicated that the presence of macromolecules hindered irreversible interactions between the cells and the quartz surface.     

Tracers for investigating pathogen fate and removal mechanisms in mesocosms

The purpose of the present investigation has been to develop a tracer suite that has application in in-situ assessment and optimization of physical and biological removal and elimination mechanisms of pathogens within laboratory scale biological treatment systems. The tracer suite includes three pathogen indicators, namely, a conserved non-viable particle (fluorescently labelled microspheres, FLM), a non-conserved non-viable particle (fluorescently labelled bioparticles, FLB), and a non-conserved viable particle (Nalidixic acid resistant E. coli, NAREC). The tracer triplet principles were developed with practical experiments on planted, and unplanted subsurface flow wetland mesocosms treating a synthetic domestic wastewater. The tracers monitor for physical removal mechanisms (FLM), elimination activity (FLB), and removal thresholds (NAREC). FLM enumeration was simplified by calibration of particle concentration with respect to acetone-extractable fluorescence. Similarly, FLB elimination was assessed by bulk fluorescence using two characteristic excitation-emission wavelength pairs: 494/519 and 220/319 nm. NAREC results indicated that first order removal kinetics may only proceed down to limiting threshold concentrations.     

Minimum inhibitory concentration (MIC) of sodium lactate for pathogens and spoilage organisms occurring in meat products

Pathogens and spoilage organisms occuring in meat products were screened in laboratory media, according to a method of Eklund (1983), in order to determine the specific inhibitory effect of lactate on growth of these microorganisms under optimum growth conditions (pH 6.5, 20°C). In general, Gram-positive bacteria were more sensitive towards lactate than Gram-negative bacteria. It was shown especially, that strains that were able to grow at water activities of 0.95 and below in the presence of NaCl (Staphylococcus aureus, Listeria monocytogenes, Brochothrix thermosphacta) were inhibited by sodium lactate (NaL). It appeared, that yeasts were resistant to large amounts of NaL (> 10% w/v). However, NaL had a specific inhibitory effect on growth of these organisms when compared to the effect of NaCl. These results indicate that lactate addition to food products with a pH near neutrality offers good prospects for shelf life prolongation.