Enterotoxigenic Profiling of Emetic Toxin‐ and Enterotoxin‐Producing Bacillus cereus,Isolated from Food,Environmental, and Clinical Samples by Multiplex PCR

Bacillus cereus comprises the largest group of endospore‐forming bacteria and can cause emetic and diarrheal food poisoning. A total of 496 B. cereus strains isolated from various sources (food, environmental, clinical) were assessed by a multiplex PCR for the presence of enterotoxin genes. The detection rate of nheA, entFM, hblC, and cytK enterotoxin genes among all B. cereus strains was 92.33%, 77.21%, 59.47%, and 47.58%, respectively. Enterotoxigenic profiles were determined in emetic toxin‐ (8 patterns) and enterotoxin‐producing strains (12 patterns). The results provide important information on toxin prevalence and toxigenic profiles of B. cereus from various sources. Our findings revealed that B. cereus must be considered a serious health hazard and Bacillus thuringiensis should be considered of a greater potential concern to food safety among all B. cereus group members. Also, there is need for intensive and continuous monitoring of products embracing both emetic toxin and enterotoxin genes.     

A multifaceted approach to harness probiotics as antagonists on plant based foods,for enhanced benefits to be reaped at a global level

Investigations into probiotics have focused on their health benefits thus far, with some of the findings finally reaching the food and pharmaceutical industries, which have used them for commercial purposes. In biocontrol research some microbes, mainly isolated from plants, have shown antagonism towards both enteric and plant pathogens, and some of them represent probiotic species. Fresh fruits and vegetables are regarded as health‐promoting dietary constituents, and if probiotics could be used to control the pathogens on them then they could turn out to be even healthier. The fresh produce industry still depends on agrochemicals and the increase in the demand for high‐priced organically grown produce indicates consumer concerns regarding the use of agrochemicals. If the potential of probiotic organisms to serve as biocontrol agents for fresh produce is exploited, all fresh produce can be made as safe as organically grown produce, and much more wholesome. This review appraises the feasibility of such a move by evaluating how research has progressed in both disciplines (probiotic and biocontrol) and suggests sharing results from research via information technology, efficient collaboration, and the use of novel molecular biological tools to achieve the objective of probiotic antagonists. © 2018 Society of Chemical Industry     

Rapid and standardized methods for detection of foodborne pathogens and mycotoxins on fresh produce

Due to the increase in consumption of fresh produce regarding to the health demand in the last decades, a considerable portion of foodborne outbreaks has been trackbacked to contaminated fresh produce, which have appeared as highly possible vehicles for foodborne outbreaks nowadays. Delays in detection of pathogens and mycotoxins on fresh produce hindered the trace-back investigations in finding the source and revealed the urgent need of rapid and reliable methods. In the frame of this review, we summarized available fast, reliable and standardized methods (conventional, molecular, rapid and recently developed methods) used for detection of the most common foodborne pathogens and mycotoxins which are the most likely causative agents of outbreaks caused by contaminated fresh produce.     

A Multiplex PCR Assay for the Rapid and Sensitive Detection of Methicillin‐Resistant Staphylococcus aureus and Simultaneous Discrimination of Staphylococcus aureus from Coagulase‐Negative Staphylococci

Abstract: Methicillin‐resistant Staphylococcus aureus (MRSA) is a global health concern, which had been detected in food and food production animals. Conventional testing for detection of MRSA takes 3 to 5 d to yield complete information of the organism and its antibiotic sensitivity pattern. So, a rapid method is needed to diagnose and treat the MRSA infections. The present study focused on the development of a multiplex PCR assay for the rapid and sensitive detection of MRSA. The assay simultaneously detected 4 genes, namely, 16S rRNA of the Staphylococcus genus, femA of S. aureus, mecA that encodes methicillin resistance, and one internal control. It was rapid and yielded results within 4 h. The analytical sensitivity and specificity of the multiplex PCR assay was evaluated by comparing it with the conventional method. The analytical sensitivity of the multiplex PCR assay at the DNA level was 10 ng DNA. The analytical specificity was evaluated with 10 reference staphylococci strains and was 100%. The diagnostic evaluation of MRSA was carried out using 360 foodborne staphylococci isolates, and showed 99.1% of specificity, 96.4% of sensitivity, 97.5% of positive predictive value, and 97.3% of negative predictive value compared to the conventional method. The inclusion of an internal control in the multiplex PCR assay is important to exclude false‐negative cases. This test can be used as an effective diagnostic and surveillance tool to investigate the spread and emergence of MRSA.     

A Five‐Element Multiplex Resonant Full‐Bridge DC‐DC Converter with a Variable Inductive Reactance

A five‐element multiplex resonant (LLCLC) full‐bridge DC‐DC converter controlled by pulse frequency modulation (PFM) is proposed in this paper. The high frequency (HF)‐link resonant DC‐DC converter proposed herein can perform wide‐range output power and voltage regulation with a narrow frequency range due to an antiresonant tank that works effectively as a wide‐range variable inductor. The advantageous characteristics of the antiresonant tank provide overcurrent protection in the case of the short‐circuited load condition as well as in the startup interval. Thus, the technical challenges of a conventional LLC DC‐DC converter can be overcome, and the reliability of the relevant switch‐mode power supplies can be improved. The operating principle of the LLCLC DC‐DC converter is described, after which its performance is evaluated in an experimental setup based on the 2.5 kW prototype. Finally, the feasibility of the proposed DC‐DC converter is discussed from a practical point of view.     

Assessment of foodborne pathogen presence in the peach supply chain and its potential risk to the end consumer

Peaches are popular, nutritious and widely consumed. Being a tree crop, it is considered a low risk fruit, with no direct water contact, and no previous foodborne disease outbreaks associated with its consumption. However, in 2014 the pioneer association between stone fruit and a foodborne illness was reported, linking Listeria monocytogenes to stone fruit. This highlights the need for better understanding of risk associated with contaminated fresh stone fruit, in order to implement adequate preventative measures. No information is available on the presence of foodborne pathogens on peaches in the supply chain. A case study approach was therefore followed to assess foodborne pathogen presence on the farm, focusing on the impact of irrigation water, facility sanitation and hygiene by collecting various fruit and environmental samples (n = 428). This study demonstrates the effectiveness of integrating basic microbial testing with safety management and risk assessment tools that can be collectively used to improve the food safety management system. No Salmonella Typhimurium was detected from samples, however, Escherichia coli O157:H7, Listeria spp. and Staphylococcus aureus were detected on fruit and environmental samples. Despite the GlobalG.A.P. certification status of the farm, livestock frequented water sources which lead to E. coli O157:H7 contamination. This conclusion was based on positive detection of foodborne pathogens from the water sources and subsequent removal of livestock which resulted in a definite decrease in pathogen detection. A number of E. coli O157:H7 and S. aureus were detected during the second year of monitoring from environmental samples and it was observed that the personal hygiene and facility sanitation was not adequately enforced. Based on feedback given to the farmer, enforcement was improved and a definite decrease in foodborne pathogens was observed in the following sampling cycle. Areas of risk that were still identified following the fourth year of monitoring included the water source used for irrigation and poor sanitation in the production and processing facilities. Limited foodborne pathogen prevalence on peaches over the full study period as well as the extended export supply chain at controlled temperatures resulted in low-to-medium calculated consumer risk. The correct and meticulous implementation of integrated and holistic pre- and post-harvest food safety management systems is therefore essential to prevent produce contamination, reduce the consumer risk and therefore ensure overall product safety.     

基于可饱和脉冲变压器的多路同步技术及其应用

多路同步的高电压脉冲有广泛应用前景。为此,对基于可饱和脉冲变压器的多路同步技术路线进行了详细阐述,并开展了实验验证。在此基础之上,提出了多次级可饱和脉冲变压器多路同步控制的新型LC发生器。在该发生器中,可饱和脉冲变压器先后承4重功能,极大地减小了系统的复杂程度。实验中,初级输入电压为910V时,输出电压幅值达到110 k V,系统总的升压倍数达121倍。此外,引入半导体断路开关,可使实验中输出脉冲的上升沿在20 ns以内。同时将半导体断路开关与电感储能型脉冲形成线相结合,提出了低阻抗方波脉冲的产生方案。研究结果表明:提出的技术方案确实可行,对脉冲功率技术向固态化、小型紧凑化以及可重复频率运行方向发展具有较大的探索意义。     

化妆品中动物源性成分多重实时荧光PCR检测方法的研究

使用优化的Chelex-100结合玻璃奶法提取膏状、液态和固态化妆品中的动物源性DNA;根据驴、马和牛线粒体16S rRNA基因序列设计通用引物和特异性探针,建立了一次性检测化妆品中驴、马和牛3种动物源性成分的多重实时荧光PCR体系,检出限均为0.001 ng。并对市售的面霜、洗面奶和面膜进行盲样检测,验证了体系的可靠性和准确性。     

Isoprenoid Biosynthesis Inhibitors Targeting Bacterial Cell Growth

We synthesized potential inhibitors of farnesyl diphosphate synthase (FPPS), undecaprenyl diphosphate synthase (UPPS), or undecaprenyl diphosphate phosphatase (UPPP), and tested them in bacterial cell growth and enzyme inhibition assays. The most active compounds were found to be bisphosphonates with electron‐withdrawing aryl‐alkyl side chains which inhibited the growth of Gram‐negative bacteria (Acinetobacter baumannii, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa) at ～1–4 μg mL^?1 levels. They were found to be potent inhibitors of FPPS; cell growth was partially “rescued” by the addition of farnesol or overexpression of FPPS, and there was synergistic activity with known isoprenoid biosynthesis pathway inhibitors. Lipophilic hydroxyalkyl phosphonic acids inhibited UPPS and UPPP at micromolar levels; they were active (～2–6 μg mL^?1) against Gram‐positive but not Gram‐negative organisms, and again exhibited synergistic activity with cell wall biosynthesis inhibitors, but only indifferent effects with other inhibitors. The results are of interest because they describe novel inhibitors of FPPS, UPPS, and UPPP with cell growth inhibitory activities as low as ～1–2 μg mL^?1.     

复合插层剂制备可膨胀石墨研究

无机化合物与有机化合物联合作复合插层剂使用,与天然鳞片石墨、浓硝酸(浓HNO3)、高锰酸钾(KMnO4)等原料经氧化酸化插层、水洗、干燥过程制备无硫可膨胀石墨,利用正交试验方法确定了最佳工艺条件:天然石墨、KMnO4、浓HNO3、P2O5、冰HAc的质量比为1∶0.08∶3.4∶0.4∶0.6,产品膨胀容积可达300 ml/g,挥发分和灰分分别比单一插层剂制得的产品低。