食品微生物外文文献2017.1.19

食品微生物外文文献2017.1.19
脉冲强光对诺如病毒和沙门及o157的灭活作用
Pulsed light (PL) inactivation of two human norovirus (HuNoV) surrogates, murine norovirus (MNV-1) and Tulane virus (TV), and two bacterial pathogens, Escherichia coli O157:H7 and Salmonella, were evaluated. The viruses and bacteria were suspended in phosphate buffered saline (PBS) to final populations of ～6 log PFU/mL and ～6 log CFU/mL, respectively. Both viral and bacterial suspensions were then irradiated by PL for different durations and the reductions of each microorganisms were determined. MNV-1 and TV were significantly (P < 0.05) more resistant to PL treatment than Salmonella and E. coli O157:H7 in PBS suspension. MNV-1, Salmonella and E. coli O157:H7 were also inoculated on strawberries and blueberries and the PL inactivation of each microorganism was determined. Lower inactivation of each microorganism was achieved on berry surfaces than in PBS suspension. This study shows that PL can induce rapid inactivation of MNV-1, TV, Salmonella and E. coli O157:H7 in clear suspension with viruses more resistant to PL treatment than bacteria. The efficacy of PL treatment is substantially influenced by food surface structure.
乳酸菌基因组学和代谢组学的研究进展
The Lactobacillus genus represents the largest and most diverse genera of all the lactic acid bacteria (LAB), encompassing species with applications in industrial, biotechnological and medical fields. The increasing number of available Lactobacillus genome sequences has allowed understanding of genetic and metabolic potential of this LAB group. Pangenome and core
genome studies are available for numerous species, demonstrating the plasticity of the Lactobacillus genomes and providing the evidence of niche adaptability. Advancements in the application of lactobacilli in the dairy industry lie in exploring the genetic background of their commercially important characteristics, such as flavour development potential or resistance to the phage attack. The integration of available genomic and metabolomic data through the generation of genome scale metabolic models has enabled the development of computational models that predict the behaviour of organisms under specific conditions and present a route to metabolic engineering. Lactobacilli are recognised as potential cell factories, confirmed by the successful production of many compounds. In this review, we discuss the current knowledge of genomics, metabolomics and metabolic engineering of the prevalent Lactobacillus species associated with the production of fermented dairy foods. In-depth understanding of their characteristics opens the possibilities for their future knowledge-based applications.
牛肉冷冻状态下的微生物
The primary objective of this study was to characterise (microbiology and physical parameters) beef carcasses and primals during chilled storage. A minor aim was to compare observed growth of key spoilage bacteria on carcasses with that predicted by ComBase and the Food Safety Spoilage Predictor (FSSP). Total viable count (TVC), total Enterobacteriacae count (TEC), Pseudomonas spp., lactic acid bacteria (LAB), Brochothrixthermosphacta and Clostridium spp. were monitored on beef carcasses (n = 30) and primals (n = 105) during chilled storage using EC Decision 2001/471/EC and ISO
sampling/laboratory procedures. The surface and/or core temperature, pH and water activity (aw) were also recorded. Clostridium (1.89 log10 cfu/cm2) and Pseudomonas spp. (2.12 log10 cfu/cm2) were initially the most prevalent bacteria on carcasses and primals, respectively. The shortest mean generation time (G) was observed on carcasses with Br. thermosphacta (20.3 h) and on primals with LAB (G = 68.8 h) and Clostridium spp. (G = 67 h). Over the course of the experiment the surface temperature dec reased from 37 °C
to 0 °C, pH from 7.07 to 5.65 and aw from 0.97 to 0.93 The observed Pseudomonas spp. and Br. thermosphacta growth was more or less within the range of predictions of Combase. In contrast, the FSSP completely overestimated the growth of LAB. This study contributes to the very limited microbiological data on beef carcasses and primals during chilling.
冰箱中牡蛎气调包装的微生物组分变化
As filter-feeding bivalves, oysters can accumulate microorganisms into their gills, causing spoilage and potential safety issues. This study aims to investigate the changes in the gill microbiota of oysters packed under air and modified atmospheres (MAs, 50% CO2: 50% N2, 70% CO2: 30% O2, and 50% CO2: 50% O2) during storage at 4 °C. The diversity of bacterial microbiota in oyster gills was profiled through polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis on the 16S rRNA gene V3 region to describe the variation during the entire storage period. The DGGE profile revealed high bacterial diversity in the air- and MA-packaged oyster gills, and the spoilage bacterial microbiota varied in the MA-packaged oyster gills. Results indicated that CO2:O2 (70%:30%) was suitable for oyster MA packaging and
that high bacterial loads in oyster gills need to be considered during storage. In addition, Lactobacillus and Lactococcus species were found to grow dominantly in fresh oyster gills under MA packaging, which supports the potential application of MA packaging for oyster storage.
干腌制猪腰猪腿的猪链球菌的生存
Dry-cured hams, shoulders and loins of Iberian pigs are highly appreciated in national and international markets. Salting, additive addition and dehydration are the main strategies to produce these ready-to-eat products. Although the dry curing process is known to reduce the load of well-known food borne pathogens, studies evaluating the viability of other microorganisms in contaminated pork have not been performed. In this work, the efficacy of the dry curing process to eliminate three swine pathogens associated with pork carcass condemnation, Streptococcus suis, Streptococcus dysgalactiae and Trueperellapyogenes, was evaluated. Results of this study highlight that the dry curing process is a suitable method to obtain safe ready-to-eat products free of these microorganisms. Although salting of dry-cured shoulders had a moderate bactericidal effect, results of this study suggest that drying and ripening were the most important stages to obtain dry-cured products free of these microorganisms.
使用噬菌体提高贝壳类中大肠杆菌的去除率
The present study investigated the potential application of the bacteriophage (or phage) phT4A, ECA2 and the phage cocktail phT4A/ECA2 to decrease the concentration of Escherichia coli during the depuration of natural and artificially contaminated cockles. Depuration in static seawater at multiplicity of infection (MOI) of 1 with single phage suspensions
of phT4A and ECA2 was the best condition, as it decreased by ～2.0 log CFU/g the concentration of E. coli in artificially contaminated cockles after a 4 h of treatment. When naturally contaminated cockles were treated in static seawater with single phage suspensions and the phage cocktail, similar decreases in the concentration of E. coli (～0.7 log CFU/g) were achieved. However, when employing the phage cocktail, a longer treatment time was required to obtain comparable results to those achieved when using single phage suspensions. When naturally contaminated cockles were depurated with phage phT4A in a recirculated seawater system (mimicking industrial depuration conditions), a 0.6 log CFU/g reduction of E. coli was achieved after a 2 h of treatment. When the depuration process was performed without phage addition, a 4 h treatment was necessary to
obtain a similar decrease. By combining phage therapy and depuration procedures, a reduction in bivalves depuration period can be achieved for, thus decreasing the cost associated with this procedure and even enhance the quality and safety of depurated bivalves destined for human consumption.
乳制品中诺如病毒的三种提取方法比较
Noroviruses (NoV) are currently the most common cause of viral foodborne diseases and RT-qPCR is widely used for their detection in food because of its sensitivity, specificity and rapidity. The ISO/TS (15216-1, 15216-2) procedures for detecting NoV and HAV in high-risk food categories such as shellfish, bottled water and vegetables were published in 2013. Milk products are less implicated in foodborne viral outbreaks but they can be contaminated with fruit added to these products or by the food handler. Thus, the development of sensitive and reliable
techniques for the detection of NoV in dairy products is needed to ensure the safety of these products. The aim of this study was to develop a RT-qPCR based method for the detection of NoV in milk products. Three methods were tested to recover NoV from artificially contaminated milk and cottage cheese. The selected method was based on the use of proteinase K and the recovery efficiencies ranged from 54.87% to 98.87% for NoV GI, 61.16%–96.50% for NoV GII. Murine norovirus and mengovirus were used as process controls and their recovery efficiencies were respectively 60.59% and 79.23%. The described method could be applied for detecting NoV in milk products for routine diagnosis needs.
溶解氧和培养基对空肠弯曲菌形成生物膜的影响
Campylobacter jejuni survival in aerobic environments has been suggested to be mediated by biofilm formation. Biofilm formation by eight C. jejuni strains under both aerobic and microaerobic conditions in different broths (Mueller-Hinton (MH), Bolton and Brucella) was quantified. The dissolved oxygen (DO) content of the broths under both incubation atmospheres was determined. Biofilm formation for all strains was highest in MH broth under both incubation atmospheres. Four strains had lower biofilm formation in MH under aerobic as compared to microaerobic incubation, while biofilm formation by the other four strains did not differ under the 2 atm. Two strains had higher biofilm formation under aerobic as compared to microaerobic atmospheres in Bolton broth. Biofilm formation by all other strains in Bolton, and all strains in Brucella broth, did not differ under the 2 atm. Under aerobic incubation DO levels in MH >Brucella> Bolton broth. Under microaerobic conditions levels in MH = Brucella> Bolton broth. Levels of DO in MH and
Brucella broth were lower under microaerobic conditions but those of Bolton did not differ under the 2 atm. Experimental conditions and especially the DO of broth media confound previous conclusions drawn about aerobic biofilm formation by C. jejuni. 热-紫外处理对液体食品的灭菌效果优化
The combination of ultraviolet radiation and heat (UV-H treatment) has been demonstrated as a promising strategy to overcome the limited UV germicidal effect in fruit juices. Nonetheless, there are so far no data regarding the efficacy of the combined process for the inactivation of bacterial foodborne pathogens in other liquid foods with different pH and composition. In this investigation, the optimum UV-H processing conditions for the inactivation of Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes, and S. aureus in chicken and vegetable broth, in addition to juices, were determined. From these data models that accurately predict the most advantageous UV-H treatment temperature and the expected synergistic lethal effect from UV and heat resistance data separately were constructed. Equations demonstrated that the optimum
UV-H treatment temperature mostly depended on heat resistance, whereas the maximum synergistic lethal effect also was affected by the UV resistance of the microorganism of concern in a particular food.
肠炎沙门鞭毛对侵袭的作用
Nontyphoidal Salmonella strains are the main source of pathogenic bacterial contamination in the poultry industry. Recently, Salmonella entericaserovar Kentucky has been recognized as the most prominent serovar on carcasses in poultry-processing plants. Previous studies showed that flagella
are one of the main factors that contribute to bacterial attachment to broiler skin. However, the precise role of flagella and the mechanism of attachment are unknown. There are two different flagellar subunits (fliC and fljB) expressed alternatively in Salmonella entericaserovars using phase variation. Here, by making deletions in genes encoding flagellar structural subunits (flgK, fliC, and fljB), and flagellar motor (motA), we were able to differentiate the role of flagella and their rotary motion in the colonization of broiler skin and cellular attachment. Utilizing a broiler skin assay, we demonstrated that the presence of FliC is necessary for attachment to broiler skin. Expression of the alternative flagellar subunit FljB enables Salmonella motility, but this subunit is unable to mediate tight attachment. Deletion of the flgK gene prevents proper flagellar assembly, making Salmonella significantly less adherent to broiler skin than the wild type. S. Kentucky with deletions in all three structural genes, fliC, fljB, and flgK, as well as a flagellar motor mutant (motA), exhibited less adhesion and invasion of Caco-2 cells, while an fljB mutant was as adherent and invasive as the wild-type strain.
IMPORTANCE In this work, we answered clearly the role of flagella in S. Kentucky attachment to the chicken skin and Caco-2 cells. We demonstrated that the presence of FliC is necessary for attachment to broiler skin. Expression of the alternative flagellar subunit FljB enables Salmonella motility, but this subunit is unable to mediate strong attachment. Deletion of the flgK gene prevents proper flagellar assembly, making Salmonella significantly less adherent to broiler skin than the wild type. S. Kentucky with deletions in all three structural genes, fliC, fljB, and flgK, as well as a flagellar motor mutant (motA), exhibited less adhesion and invasion of Caco-2 cells, while an fljB mutant was
as adherent and invasive as the wild-type strain. We expect these results will contribute to the understanding of the mechanisms of Salmonella attachment to food products.
单增李斯特菌可能是通过胃液和体外细胞侵染的主要细菌
Various Listeria monocytogenes strains may contaminate a single food product, potentially resulting in simultaneous exposure of consumers to multiple strains. However, due to bias in strain recovery, L. monocytogenes strains isolated from foods by selective enrichment (SE) might not always represent those that can better survive the immune system of a patient. We investigated the effect of cocultivation in tryptic soy broth with 0.6% yeast extract (TSB-Y) at 10°C for 8 days on (i) the detection of L. monocytogenes strains during SE with the ISO 11290-1:1996/Amd 1:2004 protocol and (ii) the in vitro virulence of strains toward the Caco-2 human colon epithelial cancer cell line following exposure to simulated gastric fluid (SGF; pH 2.0)-HCl (37°C). We determined whether the strains which were favored by SE would be effective competitors under the conditions of challenges related to gastrointestinal passage of the pathogen. Interstrain competition of L. monocytogenes in TSB-Y determined the relative population of each strain at the beginning of SE. This in turn impacted the outcome of SE (i.e., favoring survival of competitors with better fitness) and the levels exposed subsequently to SGF.
However, strong growth competitors could be outcompeted after SGF exposure and infection of Caco-2 cells by strains outgrown in TSB-Y and underdetected (or even missed) during enrichment. Our data demonstrate a preferential selection of certain L. monocytogenes strains during enrichments, often not reflecting a selective advantage of strains during infection. These
findings highlight a noteworthy scenario associated with the difficulty of matching the source of infection (food) with the L. monocytogenes isolate appearing to be the causative agent during listeriosis outbreak investigations.
系统模型的建立来描述动物粪便是果蔬感染致病菌的主要途径
The majority of foodborne outbreaks in the United States associated with the consumption of leafy greens contaminated with Escherichia coli O157:H7 have been reported during the period of July to November. A dynamic system model consisting of subsystems and inputs to the system (soil, irrigation, cattle, wild pig, and rainfall) simulating a hypothetical farm was developed. The model assumed two crops of lettuce in a year and simulated planting, irrigation, harvesting, ground preparation for the new crop, contamination of soil and plants, and survival of E. coli O157:H7. As predicted by the baseline model for crops harvested in different months from conventional fields, an estimated 13 out of 257 (5.05%) first crops harvested in July would have at least one plant with at least 1 CFU of E. coli O157:H7. Predictions indicate that no first crops would be contaminated with at least 1 CFU of E. coli O157:H7 for other months (April to June). The maximum E. coli O157:H7 concentration in a plant was higher in the second crop (27.10 CFU) than in the first crop (9.82 CFU). For the second crop, the probabilities of having at least one plant with at least 1 CFU of E. coli O157:H7 in a crop were predicted as 15/228 (6.6%), 5/333 (1.5%), 14/324 (4.3%), and 6/115 (5.2%) in August, September, October, and November, respectively. For organic fields, the probabilities of having at least one plant with ≥1 CFU of E. coli O157:H7 in a crop (3.45%) were predicted to be higher than those for the conventional fields (2.15%).
O157迫于环境压力的嗜热和苏醒加速进化
The development of resistance in foodborne pathogens to food preservation techniques is an issue of increasing concern, especially in minimally processed foods where safety relies on hurdle technology. In this context, mild heat can be used in combination with so-called nonthermal processes, such as high hydrostatic pressure (HHP), at lower individual intensities to better retain the quality of the food. However, mild stresses may increase the risk of (cross-)resistance development in the surviving population, which in turn might compromise food safety. In this investigation, we examined the evolution of Escherichia coli O157:H7 strain ATCC 43888 after recurrent exposure to progressively intensifying mild heat shocks (from 54.0°C to 60.0°C in 0.5°C increments) with intermittent resuscitation and growth of survivors. As such, mutant strains were obtained after 10 cycles of selection with ca. 106-fold higher heat resistance than that for the parental strain at 58.0°C, although this resistance did not extend to temperatures exceeding 60.0°C. Moreover, th ese mutant strains typically displayed cross-resistance against HHP shock and displayed signs of enhanced RpoS and RpoH activity. Interestingly, additional cycles of selection maintaining the intensity of the heat shock constant (58.5°C) selected for mutan t strains in which resuscitation speed, rather than resistance, appeared to be increased. Therefore, it seems that resistance and resuscitation speed are rapidly evolvable traits in E. coli ATCC 43888 that can compromise food safety.
肉桂油抑制大肠0157噬菌体的入侵和增殖
This study evaluated the inhibitory effect of cinnamon oil against Escherichia coli O157:H7 Shiga toxin (Stx) production and
further explored the underlying mechanisms. The MIC and minimum bactericidal concentration (MBC) of cinnamon oil against E. coli O157:H7 were 0.025% and 0.05% (vol/vol), respectively. Cinnamon oil significantly reduced Stx2 production and the stx2 mRNA expression that is associated with diminished Vero cell cytotoxicity. Consistently, induction of the Stx-converting phage where the stx2 gene is located, along with the total number of phages, decreased proportionally to cinnamon oil concentration. In line with decreased Stx2 phage induction, cinnamon oil at 0.75× and 1.0× MIC eliminated RecA, a key mediator of SOS response, polynucleotide phosphorylase (PNPase), and poly(A) polymerase (PAP I), which positively regulate Stx-converting phages, contributing to reduced Stx-converting phage induction and Stx production. Furthermore, cinnamon oil at 0.75× and 1.0× MIC strongly inhibited the qse BC and luxS expression associated with decreased AI-2 production, a universal quorum sensing signaling molecule. However, the expression of oxidative stress response genes oxyR, soxR, and rpoS was increased in response to cinnamon oil at 0.25× or 0.5× MIC, which may contribute to stunted bacterial growth and reduced Stx2 phage induction and Stx2 production due to the inhibitory effect of OxyR on prophage activation. Collectively, cinnamon oil inhibits Stx2 production and Stx2 phage induction in E. coli O157:H7 in multiple ways.
长时间接触导致增加了产气肠杆菌的食品感染
Bacterial cross-contamination from surfaces to food can contribute to foodborne disease. The cross-contamination rate of Enterobacteraerogenes on household surfaces was evaluated by using scenarios that differed by surface type, food type, contact time (<1, 5, 30, and 300 s), and inoculum matrix (tryptic
soy broth or peptone buffer). The surfaces used were stainless steel, tile, wood, and carpet. The food types were watermelon, bread, bread with butter, and gummy candy. Surfaces (25 cm2) were spot inoculated with 1 ml of inoculum and allowed to dry for 5 h, yielding an approximate concentration of 107 CFU/surface. Foods (with a 16-cm2 contact area) were dropped onto the surfaces from a height of 12.5 cm and left to rest as appropriate. Posttransfer, surfaces and foods were placed in sterile filter bags and homogenized or massaged, diluted, and plated on tryptic soy agar. The transfer rate was quantified as the log percent transfer from the surface to the food. Contact time, food, and surface type all had highly significant effects (P < 0.000001) on the log percent transfer of bacteria. The inoculum matrix (tryptic soy broth or peptone buffer) also had a significant effect on transfer (P = 0.013), and most interaction terms were significant. More bacteria transferred to watermelon (～0.2 to 97%) than to any other food, while the least bacteria transferred to gummy candy (～0.1 to 62%). Transfer of bacteria to bread (～0.02 to 94%) was similar to transfer of bacteria to bread with butter (～0.02 to 82%), and these transfer rates under a given set of conditions were more variable than with watermelon and gummy candy.。