The incidence of foodborne diseases has increased over the years and resulted in major public health problem globally. Foodborne pathogens can be found in various foods and it is important to detect foodborne pathogens to provide safe food supply and to prevent foodborne diseases. The conventional methods used to detect foodborne pathogen are time consuming and laborious. Hence, a variety of methods have been developed for rapid detection of foodborne pathogens as it is required in many food analyses. Rapid detection methods can be categorized into nucleic acid-based, biosensor-based and immunological-based methods. This review emphasizes on the principles and application of recent rapid methods for the detection of foodborne bacterial pathogens. Detection methods included are simple polymerase chain reaction (PCR), multiplex PCR, real-time PCR, nucleic acid sequence-based amplification (NASBA), loop-mediated isothermal amplification (LAMP) and oligonucleotide DNA microarray which classified as nucleic acid-based methods; optical, electrochemical and mass-based biosensors which classified as biosensor-based methods; enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay which classified as immunological-based methods. In general, rapid detection methods are generally time-efficient, sensitive, specific and labor-saving. The developments of rapid detection methods are vital in prevention and treatment of foodborne diseases.

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Rapid methods for the detection of foodborne bacterial pathogens: principles, applications, advantages and limitations

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Recent advances in quantitative PCR (qPCR) applications in food microbiology.

Listeria is commonly found in processed and prepared foods and listeriosis is associated with high morbidity and mortality. Preventative measures are well prescribed and monitoring and voluntary recall of contaminated products has resulted in a 44% reduction in the prevalence of perinatal listeriosis in the USA. Pregnant women are at high risk for listeriosis, but symptoms are non-specific and diagnosis is difficult. The intracellular life-cycle of Listeria protects the bacterium from host innate and adaptive immune responses. Antibiotic treatment requires agents able to penetrate, distribute, and remain stable within host cells. Prolonged use of high-dose ampicillin can significantly improve neonatal outcome.

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Listeriosis in human pregnancy: a systematic review.

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing. We analyze the biologically relevant properties of QDs focusing on the following topics: QD surface treatment and stability, labeling of cellular structures and receptors with QDs, incorporation of QDs in living cells, cytotoxicity of QDs and influence of the biological environment on the biological and optical properties of QDs. Initially, we consider utilization of QDs as agents in high-resolution bioimaging techniques that can provide information at the molecular levels. The diverse range of modern live-cell QD-based imaging techniques with resolution far beyond the diffraction limit of light is examined. In each technique, we discuss the pros and cons of QD use and deliberate how QDs can be further engineered to facilitate their application in the respective imaging techniques and to produce significant improvements in resolution. Then we review QD-based point-of-care bioassays, bioprobes, and biosensors designed in different formats ranging from analytic biochemistry assays and ELISA, to novel point-of-care smartphone integrated QD-based biotests. Here, a wide range of QD-based fluorescence bioassays with optical transduction, elecrochemiluminescence and photoelectrochemical assays are discussed. Finally, this review provides an analysis of the prospects of application of QDs in selected important areas of biology.

Application of semiconductor quantum dots in bioimaging and biosensing.

Magnesium oxide nanoparticles (MgO nanoparticles, with average size of 20 nm) have considerable potential as antimicrobial agents in food safety applications due to their structure, surface properties, and stability. The aim of this work was to investigate the antibacterial effects and mechanism of action of MgO nanoparticles against several important foodborne pathogens. Resazurin (a redox sensitive dye) microplate assay was used for measuring growth inhibition of bacteria treated with MgO nanoparticles. The minimal inhibitory concentrations of MgO nanoparticles to 104 colony-forming unit/ml (CFU/ml) of Campylobacter jejuni, Escherichia coli O157:H7, and Salmonella Enteritidis were determined to be 0.5, 1 and 1 mg/ml, respectively. To completely inactivate 108−9 CFU/ml bacterial cells in 4 h, a minimal concentration of 2 mg/ml MgO nanoparticles was required for C. jejuni whereas E. coli O157:H7 and Salmonella Enteritidis required at least 8 mg/ml nanoparticles. Scanning electron microscopy examination revealed clear morphological changes and membrane structural damage in the cells treated with MgO nanoparticles. A quantitative real-time PCR combined with ethidium monoazide pretreatment confirmed cell membrane permeability was increased after exposure to the nanoparticles. In a cell free assay, a low level (1.1 μM) of H2O2 was detected in the nanoparticle suspensions. Consistently, MgO nanoparticles greatly induced the gene expression of KatA, a sole catalase in C. jejuni for breaking down H2O2 to H2O and O2. MgO nanoparticles have strong antibacterial activity against three important foodborne pathogens. The interaction of nanoparticles with bacterial cells causes cell membrane leakage, induces oxidative stress, and ultimately leads to cell death.

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Study on the mechanism of antibacterial action of magnesium oxide nanoparticles against foodborne pathogens

To achieve an effective detection of Salmonella spp., Escherichia coli O157, and Listeria monocytogenes in meat products, a multiplex real-time polymerase chain reaction (PCR) coupled with a multipathogen enrichment strategy was developed in this study. Pathogen-specific DNA sequences in the invA, rfbE, and hlyA genes were employed to design primers and TaqMan probes for identifying Salmonella spp., E. coli O157, and L. monocytogenes, respectively. An internal amplification control (IAC) utilizing a novel DNA sequence from human adenovirus was incorporated into the multiplex PCR assay to indicate false-negative results. Concurrent amplifications of multiple targets and IAC were thoroughly evaluated and optimized to minimize PCR competitions. Combined with a multipathogen enrichment in a selective enrichment broth for Salmonella, Escherichia, and Listeria (SEL), the multiplex real-time PCR assay was able to simultaneously detect all of the three organisms in artificially contaminated ground beef a...

A Multiplex Real-Time Polymerase Chain Reaction for Simultaneous Detection of Salmonella spp., Escherichia coli O157, and Listeria monocytogenes in Meat Products

Development of an oligonucleotide-based microarray to detect multiple foodborne pathogens

In food processing, the temperature is usually reduced to limit bacterial reproduction and maintain food safety. However, Staphylococcus aureus can adapt to low temperatures by controlling gene expression and protein activity, although its survival strategies normally vary between different strains. The present study investigated the molecular mechanisms of S. aureus with different survival strategies in response to low temperatures (4 °C). The survival curve showed that strain BA-26 was inactivated by 6.0 logCFU/mL after 4 weeks of low-temperature treatment, while strain BB-11 only decreased by 1.8 logCFU/mL. Intracellular nucleic acid leakage, transmission electron microscopy, and confocal laser scanning microscopy analyses revealed better cell membrane integrity of strain BB-11 than that of strain BA-26 after low-temperature treatment. Regarding oxidative stress, the superoxide dismutase activity and the reduced glutathione content in BB-11 were higher than those in BA-26; thus, BB-11 contained less malondialdehyde than BA-26. RNA-seq showed a significantly upregulated expression of the fatty acid biosynthesis in membrane gene (fabG) in BB-11 compared with BA-26 because of the damaged cell membrane. Then, catalase (katA), reduced glutathione (grxC), and peroxidase (ahpC) were found to be significantly upregulated in BB-11, leading to an increase in the oxidative stress response, but BA-26-related genes were downregulated. NADH dehydrogenase (nadE) and α-glucosidase (malA) were upregulated in the cold-tolerant strain BB-11 but were downregulated in the cold-sensitive strain BA-26, suggesting that energy metabolism might play a role in S. aureus under low-temperature stress. Furthermore, defense mechanisms, such as those involving asp23, greA, and yafY, played a pivotal role in the response of BB-11 to stress. The study provided a new perspective for understanding the survival mechanism of S. aureus at low temperatures.

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Comparative Transcriptomic Analysis of Staphylococcus aureus Reveals the Genes Involved in Survival at Low Temperature

Transcriptome analysis reveals the molecular mechanism of cinnamaldehyde against Bacillus cereus spores in ready-to-eat beef.

Listeria monocytogenes is a cold tolerant foodborne pathogen that frequently detected in ground pork stored at low temperature. The study firstly evaluated the inhibitory effect of cinnamaldehyde on Listeria monocytogenes at 4°C and the mechanism by which cinnamaldehyde interferes with the adaptive gene regulation system. When low temperature and cinnamaldehyde were combined for treating L. monocytogenes, the time required to cause a reduction by 2 log CFU/g (t 2.0) was decreased along with the increase of cinnamaldehyde concentration, although cinnamaldehyde may produce an unpleasant but acceptable odor. Transmission electron microscopy (TEM) results showed severe rupture of the cell envelope and leakage of cytoplasmic contents in cells treated with a combination treatment of cinnamaldehyde and low temperature, but the effect of individual treatment is not obvious. Real-time quantitative PCR results revealed that the stress resistance genes (gbuA, gbuB, gadD2, groEL, rli60 and ilvD), regulatory genes (prfA, sigB, codY and luxS) and cold shock response genes (cspA, cspB and cspD) were actively involved in the response to the low temperature. However, the combination of cinnamaldehyde and low temperature treatment disturb the gene regulation. Molecular docking results further indicate that cinnamaldehyde may interact with protein PrfA and LuxS amino acid residues through hydrogen bonding, thus interfering with regulator activity. The results firstly indicates that cinnamaldehyde has a synergistic inhibition effect on L. monocytogenes in cold stored ground pork by rupturing cell envelop and disturbing stress regulatory gene expression, which provides a new idea for the safety control of chilled meat. 

Biao Suo

Papers

A Multiplex Real-Time Polymerase Chain Reaction for Simultaneous Detection of Salmonella spp., Escherichia coli O157, and Listeria monocytogenes in Meat Products

Development of an oligonucleotide-based microarray to detect multiple foodborne pathogens

Comparative Transcriptomic Analysis of Staphylococcus aureus Reveals the Genes Involved in Survival at Low Temperature

Transcriptome analysis reveals the molecular mechanism of cinnamaldehyde against Bacillus cereus spores in ready-to-eat beef.

Cinnamaldehyde inactivates Listeria monocytogenes at a low temperature in ground pork by disturbing the expression of stress regulatory genes