Search

Rapid, sensitive, point-of-care detection of pathogenic bacteria is important for food safety. In this study, we developed a novel quantum dot nanobeads-labelled lateral flow immunoassay strip (QBs-labelled LFIAS) combined with strand displacement loop-mediated isothermal amplification (SD-LAMP) for quantitative Salmonella Typhimurium (ST) detection. Quantum dot nanobeads (QBs) served as fluorescence reporters, providing good detection efficiency. The customizable strand displacement (SD) probe was used in LAMP to improve the specificity of the method and prevent by-product capture. Detection was based on a sandwich immunoassay. A fluorescence strip reader measured the fluorescence intensity (FI) of the test (T) line and control (C) line. The linear detection range of the strip was 102–108 CFU·mL−1. The visual limit of detection was 103 CFU·mL−1, indicating that the system was 10-fold more sensitive than AuNPs-labelled test strips. ST specificity was analyzed in accordance with agarose gel outputs of PCR and SD-LAMP. We detected ST in foods with an acceptable recovery of 85%–110%. The method is rapid, simple, almost equipment-free, and suitable for bacterial detection in foods and for clinical diagnosis.

This study investigated the antipathogenic activity and probiotic potential of indigenous lactic acid bacteria (LAB) isolated from Chinese homemade pickles. In total, 27 samples were collected from different sites in China. Fifty-nine yielded pure colonies were identified by 16S rRNA gene sequencing as LAB and were initially evaluated for the antibacterial activity in vitro. Initial screening yielded Lactobacillus plantarum GS083, GS086, and GS090, which showed a broad-spectrum antibacterial activity against food-borne pathogens, especially multidrug-resistant pathogens. Meanwhile, organic acids were mainly responsible for the antimicrobial activity of the LAB strains, and the most abundant of these was lactic acid (19.32 ± 0.95 to 24.79 ± 0.40 g/l). Additionally, three L. plantarum strains demonstrated several basic probiotic characteristics including cell surface hydrophobicity, autoaggregation, and survival under gastrointestinal (GI) tract conditions. The safety of these isolates was also evaluated based on their antibiotic susceptibility, hemolytic risk, bile salt hydrolase activity, and existence of virulence or antibiotic resistance genes. All strains were safe at both the genomic and phenotypic levels. Therefore, L. plantarum GS083, GS086, and GS090 are fairly promising probiotic candidates and may be favorable for use as preservatives in the food industry.

The abundant information provided by the pan-genome analysis approach reveals the diversity among Listeria monocytogenes serotypes. The objective of this study was to mine novel target genes using pan-genome analysis for multiplex PCR detection and differentiation of the major L. monocytogenes serotypes present in food. Pan-genome analysis and PCR validation revealed a total of 10 specific targets: one for lineage I, two for serogroup I.1, one for serogroup I.2, two for lineage II, one for serogroup II.1, three for lineage III. Primers for the novel targets were highly specific in individual reactions. The detection limits were 103–104 colony-forming units (CFU)/mL in pure bacterial cultures, meeting the requirements of molecular detection. Based on these novel targets, two new “lineage” multiplex PCR assays were developed to simultaneously distinguish between three lineages (I, II, and III) and five major serotypes (1/2a, 1/2b, 1/2c, 4b, and 4c) of L. monocytogenes. The detection limits of lineage I and lineage II&III mPCRs were 0.771 pg/μL and 1.76 pg/μL genomic DNA, respectively. The specificity of the mPCRs was robustly verified using other L. monocytogenes and non-L. monocytogenes serotypes. These results suggest that the two “lineage” multiplex PCRs based on novel targets offer a promising approach for accurate, sensitive, and rapid identification of L. monocytogenes serotypes.

Wuwei Qingzuo San (WWQZS), as a renowned traditional Mongolian patent medicine approved by Chinese State Food and Drug Administration, is used to treat hyperlipidemia, indigestion, and other ailments related to disorder of production of essence and phlegm, a typical abnormal metabolism of blood in traditional Mongolian medicine. A combination of network pharmacology and validation experiments in hyperlipidemia hamster is used to understand the potential mechanism of WWQZS for hypolipidemic effects, further for an integrated concept of traditional theory, bioactive constituents, and molecular mechanism for TMM. Through network pharmacology, we obtained 212 components, 219 predicted targets, and 349 known hyperlipidemia-related targets form public database and used Metascape to carry out enrichment analysis of 43 potential and 45 candidate targets to imply numerous BP concerned with metabolism of lipid, regulation of kinases and MF related to lipid binding, phosphatase binding, and receptor ligand activity that are involved in anti-hyperlipidemia. In addition, KEGG pathways that explicated hypolipidemic effect were involved in pathways including metabolism associated with kinase function according to MAPK signaling pathway, AMPK signaling pathway, and PI3K-Akt signaling pathway. Meanwhile, in HFD-induced hamster model, WWQZS could significantly reduce TC and ALT and help decrease TG, LDL-C as well; liver pathological section implied that WWQZS could relieve liver damage and lipid accumulation. Western blot indicated that WWQZS may upregulate CYP7A1 and activate AMPK to suppress the expression of HMGCR in livers. In conclusion, our results suggest that WWQSZS plays important dual hypolipidemic and liver-protective role in livers in HFD-induced hamster model. Through this research, a new reference is also provided to other researches in the study of ethnopharmacology.

Listeria monocytogenes is an important foodborne pathogen worldwide, with a high mortality rate of 20%–30% for vulnerable persons. The aim of this study was to determine the distribution, contamination routes, and persistence of L. monocytogenes in a mushroom plant. A total of 204 samples collected during four sampling periods within a one-year time interval, with 27.0% (55/204) were positive for L. monocytogenes. A total of 60 representative L. monocytogenes strains were selected for further analysis based on serogrouping and enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) fingerprints. Multiplex PCR showed serogroups I.1 (1/2a-3a) and II.2 (1/2b-3b-7) accounted for 68.3% (41/60) and 31.7% (19/60), respectively, of the samples. ST8 strains were isolated from the mycelium-scraping phase to the harvest phase by multilocus sequence typing. These strains had identical ERIC-PCR fingerprints, suggesting that the mycelium-scraping machine was the main contamination source. Sequence types (ST) 8 (61.7%, 37/60) and 87 (23.3%, 14/60) were predominant and repeatedly isolated within a one-year seasonal investigation, indicating that ST8 and ST87 persist in this plant. The minimum inhibitory concentrations of commonly used quaternary ammonium compounds for the 60 isolates were ≥4 μg/mL, indicating that the persistence we observed may be associated with biocide tolerance. In addition, all strains harbored nine virulent genes (prfA, hly, mpl, actA, iap, plcA, plcB, inlA, and inlB). Only ST87 strains carried ptsA (representing LIPI-4), but none of the strains harbored llsX (representing LIPI-3). These results indicate that ST87 strains pose a potential public risk to consumers. All isolates were susceptible to 13 antimicrobials, except for levofloxacin (1.7%, 1/60), erythromycin (3.3%, 2/60), and clindamycin (88.3%, 53/60). This study is the first to explore the contamination routes and persistence of L. monocytogenes in a Hypsizigus marmoreus production facility. Critical disinfection measures should be adopted to eliminate its persistence throughout processing.

Cronobacter strains harboring CRISPR-Cas systems are important foodborne pathogens that cause serious neonatal infections. CRISPR typing is a new molecular subtyping method to track the sources of pathogenic bacterial outbreaks and shows a promise in typing Cronobacter, however, this molecular typing procedure using routine PCR method has not been established. Therefore, the purpose of this study was to establish such methodology, 257 isolates of Cronobacter sakazakii, C. malonaticus, and C. dublinensis were used to verify the feasibility of the method. Results showed that 161 C. sakazakii strains could be divided into 129 CRISPR types (CTs), among which CT15 (n = 7) was the most prevalent CT followed by CT6 (n = 4). Further, 65 C. malonaticus strains were divided into 42 CTs and CT23 (n = 8) was the most prevalent followed by CT2, CT3, and CT13 (n = 4). Finally, 31 C. dublinensis strains belonged to 31 CTs. There was also a relationship among CT, sequence type (ST), food types, and serotype. Compared to multi-locus sequence typing (MLST), this new molecular method has greater power to distinguish similar strains and had better accordance with whole genome sequence typing (WGST). More importantly, some lineages were found to harbor conserved ancestral spacers ahead of their divergent specific spacer sequences; this can be exploited to infer the divergent evolution of Cronobacter and provide phylogenetic information reflecting common origins. Compared to WGST, CRISPR typing method is simpler and more affordable, it could be used to identify sources of Cronobacter food-borne outbreaks, from clinical cases to food sources and the production sites.

Various molecular techniques have been introduced for Salmonella detection. Loop-mediated isothermal amplification (LAMP) is a simple and easy-to-operate detection method compared with conventional PCR. However, the specificity and efficiency of DNA amplification relies on the selected target sequence. In this study, we aimed to identify new molecular targets and develop a LAMP-based method for the rapid detection of Salmonella in food samples. Using bioinformatics analysis and PCR verification, 3 and 10 molecular targets respectively unique to Salmonella genus and S. enterica were identified. The limit of detection (LOD) for these targets ranged from 2.1 × 102 to 2.1 × 103 CFU/mL. Of these, the ssaQ gene yielded 100% positive results upon testing with 23 most commonly reported Salmonella serovars and showed no cross-reaction with 22 non-Salmonella strains. Furthermore, its LOD was 2.1 × 101 CFU/mL, making it 10-fold more sensitive than the optimal PCR-based method. Therefore, the ssaQ gene was selected as the target gene to detect Salmonella using LAMP. The ability of the ssaQ-based LAMP method of detecting Salmonella in food samples was consistent with that of the standard culture method. The developed method has potential applications in identifying Salmonella contamination in food as well as for rapid and precise tracing of contamination sources in clinical diagnostics.

Salmonella is a leading cause of foodborne disease worldwide and ready-to-eat (RTE) foods are regarded as a major source of infection and outbreak. In recent years, the consumption of Chinese RTE foods has raised markedly with the pace of life increasing. However, the prevalence of Salmonella in these foods in China and its potential risk to public health has not been well determined and evaluated. This study was undertaken to investigate the prevalence of Salmonella in Chinese retail RTE food products and to determine serotype distribution, antimicrobial resistance, virulence, and genetic diversity of recovered Salmonella isolates. Out of the 539 RTE food products collected and tested from July 2011 to May 2014, 19 (3.5%) were positive for Salmonella . The contamination levels of Salmonella were mostly in the range of 0.3–10 most probable number (MPN)/g, with one sample exceeding 110 MPN/g. Among the 50 isolates identified, 37 isolates (74.0%) were resistant to at least one antimicrobial, while 21 isolates (42.0%) were resistant to more than three antimicrobials. High rates of resistance were observed for tetracycline (56.0%), ampicillin (38.0%), and streptomycin (34.0%). PCR analysis of 15 virulence genes showed that the avrA , ssaQ , mgtC , siiD , sopB , and bcfC genes were detected in all 50 isolates, whereas the genes located on plasmid and prophage varied significantly among the isolates. Ten distinct serovars were identified and S . Derby, S. Meleagridis, S . Enteritidis, and S. Senftenberg were the most prevalent serovars. A total of 11 sequence types by multilocus sequence typing and 20 profiles by pulsed-field gel electrophoresis were generated for the 20 selected isolates and the combination of these two methods presented a better knowledge of genetic diversity of Salmonella isolates. The study provided a systematical surveillance on prevalence of Salmonella in Chinese RTE foods and indicates its potential risk to public health.

Cronobacter species (Cronobacter spp.) are important foodborne pathogens that can infect and cause serious life-threatening diseases in infants and immunocompromised elderly. This study aimed to acquire data on Cronobacter spp. contamination of aquatic products in China from 2011 to 2016. In total, 800 aquatic products were tested, and the overall contamination rate for Cronobacter spp. was 3.9% (31/800). The average contamination level of the positive samples was 2.05 MPN/g. Four species and nine serotypes were identified among 33 isolates, of which the C. sakazakii serogroup O1 (n = 9) was the primary serotype. The majority of Cronobacter spp. strains harbored highest resistance against cephalothin (84.8%), followed by tetracycline (6.1%), trimethoprim/sulfameth-oxazole (3.0%) and chloramphenicol (3.0%). Two isolates were resistant to three antibiotics. In total, 26 sequence types and 33 CRISPR types (including 6 new STs and 26 new CTs) were identified, which indicates the extremely high diversity of Cronobacter spp. in aquatic products. Pathogenic C. sakazakii ST4, ST1, and C. malonaticus ST7 were also observed. Overall, this large-scale study revealed the relatively low prevalence and high genetic diversity of Cronobacter spp. in aquatic products in China, and the findings provide valuable information that can guide the establishment of effective measures for the control and precaution of Cronobacter spp. in aquatic products during production processes.

Cronobacter strains harboring the CRISPR-Cas system are important foodborne pathogens causing serious neonatal infections. However, the specific role of the CRISPR-Cas system in bacterial evolution remains relatively unexplored. In this study, we investigated the impact of the CRISPR-Cas system on Cronobacter evolution and obtained 137 new whole-genome Cronobacter sequences by next-generation sequencing technology. Among the strains examined ( n = 240), 90.6% (193/213) of prevalent species Cronobacter sakazakii , Cronobacter malonaticus , and Cronobacter dublinensis strains had intact CRISPR-Cas systems. Two rare species, Cronobacter condimenti ( n = 2) and Cronobacter universalis ( n = 6), lacked and preserved the CRISPR-Cas system at a low frequency (1/6), respectively. These results suggest that the presence of one CRISPR-Cas system is important for a Cronobacter species to maintain genome homeostasis for survival. The Cronobacter ancestral strain is likely to have harbored both subtype I-E and I-F CRISPR-Cas systems; during the long evolutionary process, subtype I-E was retained while subtype I-F selectively degenerated in Cronobacter species and was even lost by the major Cronobacter pathovars. Moreover, significantly higher CRISPR activity was observed in the plant-associated species C . dublinensis than in the virulence-related species C. sakazakii and C . malonaticus . Similar spacers of CRISPR arrays were rarely found among species, suggesting intensive change through adaptive acquisition and loss. Differentiated CRISPR activity appears to be the product of environmental selective pressure and might contribute to the bidirectional divergence and speciation of Cronobacter . IMPORTANCE This study reports the evolutionary history of Cronobacter under the selective pressure of the CRISPR-Cas system. One CRISPR-Cas system in Cronobacter is important for maintaining genome homeostasis, whereas two types of systems may be redundant and not conducive to acquiring beneficial DNA for environmental adaptation and pathogenicity. Differentiated CRISPR activity has contributed to the bidirectional divergence and genetic diversity of Cronobacter . This perspective makes a significant contribution to the literature by providing new insights into CRISPR-Cas systems in general, while further expanding the roles of CRISPR beyond conferring adaptive immunity and demonstrating a link to adaptation and species divergence in a genus. Moreover, our study provides new insights into the balance between genome homeostasis and the uptake of beneficial DNA related to CRISPR-based activity in the evolution of Cronobacter .

This study aimed to estimate the extent and level of Salmonella contamination of aquatic food products in China, and to determine serotype, virulotype, and the antimicrobial resistance profiles of recovered Salmonella isolates. Out of 554 samples collected from July 2011 to May 2014, 86 (15.5%) tested positive for Salmonella. The highest contamination rate occurred in oysters (23.1%, 6/26), followed by freshwater fish (18.6%, 43/231), shrimp (13.0%, 13/100), and saltwater fish (12.2%, 24/197). The contamination levels generally corresponded to a most probable number (MPN)/g of 0.3–10, although one sample exceeded 110 MPN/g. Among the 103 isolates, S. Typhimurium, S. Wandsworth, S. Thompson, and S. Derby were the most prevalent serovars. Sixty-eight isolates (66.0%) were resistant to at least one antimicrobial, and 35 (34.0%) were resistant to more than three. High rates of resistance were observed for tetracycline (35.9%), ampicillin (28.2%), nalidixic acid (26.2%), trimethoprim-sulfamethoxazole (25.2%), chloramphenicol (20.4%) and streptomycin (18.4%). Of note, S. Thompson isolates exhibited resistance to multiple extended-spectrum cephalosporins, ciprofloxacin, and other antimicrobials. PCR analysis of 15 virulence genes showed that ssaQ, mgtC, siiD, sopB, and bcfC were present in all 103 isolates, whereas the remaining loci were variably distributed. S. Typhimurium, S. Enteritidis, and S. Weltevreden isolates exhibited a wider range of pathogenicity determinants compared with the other strains. Our study provides a comprehensive surveillance on prevalence of Salmonella in aquatic food products from China and indicates its potential risk to public health. These data are valuable for epidemiological studies, risk management, and public health strategies.

Yb3+ doped BaGd2ZnO5 phosphor was synthesized via sol–gel method. X-ray diffraction, scanning electron microscopy and photoluminescence spectra were employed to characterize the as-obtained products. Upon 274 nm excitation, a single strong narrow-band emission from 2F5/2 → 2F7/2 of Yb3+ ion around 977 nm was obtained in Yb3+ doped BaGd2ZnO5 phosphor, which was well suited to efficient absorption in a silicon solar cell. After adding Ce3+ into Yb3+-doped BaGd2ZnO5, the excitation spectra of samples monitored at 977 nm indicated that the excitation peaks were in the broad range from 230 nm to 400 nm, which covered ultraviolet and blue light with poor solar cell spectral response. Furthermore, Er3+ was introduced into Yb3+-doped BaGd2ZnO5 phosphor to prove the high energy transfer efficiency from Gd3+ ion to Yb3+ ion by comparing it with that of Er3+ ion to Yb3+ ion. With access to broad-band absorption, narrow-band emission as well as high energy transfer efficiency, Ce3+, Yb3+-codoped BaGd2ZnO5 may have potential applications in modifying the solar spectrum to enhance the efficiency of silicon solar cells.

BaGd 2 ZnO 5 : Dy 3+ , Yb 3+ was successfully synthesized by the sol–gel method. The crystal structure and morphology of the samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscope. Under 3 W 971 nm near-infrared laser excitation, the near-infrared emission of phosphors was intense. The dependence of the up-conversion emission intensities of the phosphors on the working power of laser diode was obtained as an evidence for the energy transfer from Yb 3+ to Dy 3+ . In comparison, under excitation of 354 nm light, the near-infrared quantum cutting for the BaGd 2 ZnO 5 : Dy 3+ , Yb 3+ samples is proved by the emission spectra. The corresponding quantum cutting mechanisms are discussed through the energy level. The maximum quantum efficiency calculated approaches 158.0%. This study has the prospect to be applied in silicon-based solar cells to promote the conversion efficiency.

Staphylococcus aureus, particularly methicillin-resistant S.aureus (MRSA), is a life-threatening pathogen in humans, and its presence in food is a public health concern. MRSA has been identified in foods in China, but little information is available regarding MRSA in ready-to-eat (RTE) foods. We aimed to investigate the prevalence of S. aureus and MRSA in Chinese retail RTE foods. All isolated S. aureus were tested for antimicrobial susceptibility, and MRSA isolates were further characterized by multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. Of the 550 RTE foods collected from 2011 to 2014, 69 (12.5%) were positive for S. aureus. Contamination levels were mostly in the range of 0.3-10 most probable number (MPN)/g, with five samples exceeding 10 MPN/g. Of the 69 S. aureus isolates, seven were identified as MRSA by cefoxitin disc diffusion test. Six isolates were mecA-positive, while no mecC-positive isolates were identified. In total, 75.8% (47/62) of the methicillin-susceptible S. aureus isolates and all of the MRSA isolates were resistant to three or more antibiotics. Amongst the MRSA isolates, four were identified as community-acquired strains (ST59-MRSA-IVa (n = 2), ST338-MRSA-V, ST1-MRSA-V), while one was a livestock-associated strain (ST9, harboring an unreported SCCmec type 2C2). One novel sequence type was identified (ST3239), the SCCmec gene of which could not be typed. Overall, our findings showed that Chinese retail RTE foods are likely vehicles for transmission of multidrug-resistant S. aureus and MRSA lineages. This is a serious public health risk and highlights the need to implement good hygiene practices.

Salmonella enterica subsp. enterica serovar 1,4,[5],12:i:- is a monophasic variant of Salmonella Typhimurium, which has recently been recognized as an emerging cause of infection worldwide. This bacterium has also ranked among the four most frequent serovars causing human salmonellosis in China. However, there are no reports on its contamination in Chinese food. Serotyping, polymerase chain reaction, antibiotic resistance, virulotyping, and multilocus sequence typing (MLST) assays were used to investigate the prevalence of this serological variant in food products in China, and to determine phenotypic and genotypic difference of monophasic isolates and Salmonella Typhimurium isolated over the same period. Salmonella 1,4,[5],12:i:- was prevalent in various food sources, including beef, pork, chicken, and pigeon. The study also confirmed the high prevalence (53.8%) of resistance to ampicillin, streptomycin, sulfonamides, and tetracycline in Salmonella 1,4,[5],12:i:-, which was higher than that in Salmonella Typhimurium. Moreover, Salmonella 1,4,[5],12:i:- isolates in our study were different from Salmonella Typhimurium isolates by the absence of three plasmid-borne genes (spvC, pefA, and rck) and the presence of gipA in all isolates. All Salmonella 1,4,[5],12:i:- isolates demonstrated MLST pattern ST34. Genomic deletions within the fljBA operon and surrounding genes were only found in Salmonella 1,4,[5],12:i:- isolates, with all isolates containing a deletion of fljB. However, hin and iroB were identified in all Salmonella 1,4,[5],12:i:- isolates. Three different deletion profiles were observed and two of them were different from the reported Salmonella 1,4,[5],12:i:- clones from Spain, America, and Italy, which provided some new evidence on the independent evolution of the multiple successful monophasic clones from Salmonella Typhimurium ancestors. This study is the first report of Salmonella 1,4,[5],12:i:- in food products from China. The data are more comprehensive and representative, providing valuable information for epidemiological studies, risk management, and public health strategies.

Nd3+ and Yb3+ doped BaGd2ZnO5 phosphors were synthesized via high temperature solid-state method. The composition and structure have been investigated by the X-ray powder diffraction. The near-infrared quantum cutting for BaGd2ZnO5: Nd3+, Yb3+ is proved by the visible and near-infrared excitation, emission spectra and decay curves. Upon 359 nm excitation, visible and near-infrared emission of Nd3+ decrease with Yb3+ concentration increasing, and the intensities of 978 nm near-infrared emission of Yb3+ increase firstly and then decrease because of concentration quenching. The corresponding quantum cutting mechanism has been discussed through the energy level diagram. The maximum energy transfer efficiency calculated approaches 31.9%. Furthermore, the quenching concentration of Yb3+ is 7%. This study has prospect to be applied in the silicon-based solar cells to progress the conversion efficiency.

A micorwave phase shifter has been made by using YBCO superconducting thin film, In this paper, We describe the fabrication of phase shifter, and present the experimental results. The theoretic analyses are also presented.