Detection of Listeria monocytogenes in salmon using the Probelia polymerase chain reaction system

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

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.

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

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.

Sensitive Listeria spp. immunoassay based on europium(III) nanoparticulate labels using time-resolved fluorescence

Listeria spp. are Gram-positive rod shaped bacteria found universally in the environment. Pathogenic Listeria monocytogenes is seldom harmful to healthy adults, but can cause serious disease, listeriosis, especially to pregnant women, neonates, and elderly or immunocompromised people. Conventional methods for screening Listeria in food samples are time consuming and laborious, involving the use of a range of liquid media and plate cultures. In the current study, the total analysis time was shortened by employing a sensitive Listeria assay, which was able to detect the bacteria in low concentrations. Sensitivity of the sandwich immunoassay was substantially improved by utilizing europium(III)-chelate containing latex nanoparticles as tracers. Each 107 nm nanoparticle contained approximately 31000 europium(III)-chelates which enhanced the specific activity of the label. The sensitive nanoparticulate immunoassay developed for Listeria spp. was performed in one-step and two-step formats. One-step assay was notably faster, 15 min, and simpler to execute having analytical sensitivity of 300 CFU/ml and a dynamic range of three orders of magnitude. The sensitivity, 20 CFU/ml, of the 4 h two-step assay clearly exceeded that of the one-step assay, and the dynamic range was nearly five orders of magnitude. Food and environmental samples were measured against a commercial L. monocytogenes immunoassay with good correlation. The developed sensitive assay enabled shorter sample enrichment times and, therefore, faster analysis of Listeria spp. Obviously the detection of several other bacteria can also be enhanced by applying the nanoparticle assay technology.

Evaluation of Effects of Primary and Secondary Enrichment for the Detection ofListeria monocytogenesby Real-Time PCR in Retail Ground Chicken Meat

A SYBR Green I based real-time PCR assay with inlA-specific oligonucleotide primers was developed for easy and rapid detection of Listeria monocytogenes in a model food that usually has a high incidence of contamination with this pathogen. Results with pure cultures and artificially contaminated chicken meat samples indicate that the PCR assay was highly specific and sensitive. The melting point analysis of the 160 bp amplified DNA fragment was different for L. monocytogenes isolates of the two major phylogenetic divisions of the species, 1 and 2. The assay was then used to survey retail ground chicken meat for contamination with L. monocytogenes. Thirty-seven samples were enriched according to the United States Department of Agriculture culture assays to detect L. monocytogenes on meat. The use and efficiency of PCR assay was examined following both primary and secondary enrichments, which were also plated on chromogenic agar for enumeration of L. monocytogenes and nonpathogenic Listeria spp. to investigate the discrepancies between culture and PCR. Overall, L. monocytogenes was detected in 75% of the samples. Primary enrichment yielded detection rates of 70% and 37% for culture and PCR, respectively. The corresponding rates for secondary enrichment were 54% and 70%, respectively. Test sensitivity is therefore influenced by the type of enrichment and is probably related not only to the limited growth of L. monocytogenes in the primary enrichment media (false-negative PCR results), but also to the high populations of nonpathogenic Listeria spp. in the secondary enrichment broths (false-negative culture results). The main challenge of rapid PCR-based detection of L. monocytogenes from food is the poor sensitivity of primary enrichment media. The improvement of enrichment conditions may help increase assay sensitivity.

Detection of Listeria monocytogenes and the toxin listeriolysin O in food

Listeria monocytogenes is an emerging bacterial foodborne pathogen responsible for listeriosis, an illness characterized by meningitis, encephalitis, and septicaemia. Less commonly, infection can result in cutaneous lesions and flu-like symptoms. In pregnant women, the pathogen can cause bacteraemia, and stillbirth or premature birth of the fetus. The mortality rate for those contracting listeriosis is approximately 20%. Currently, the United States has a zero tolerance policy regarding the presence of L. monocytogenes in food, while Canada allows only 100 cfu/g of food. As such, it is essential to be able to detect the pathogen in low numbers in food samples. One of the best ways to detect and confirm the pathogen is through the detection of one of the virulence factors, listeriolysin O (LLO) produced by the microorganism. The LLO-encoding gene (hlyA) is present only in virulent strains of the species and is required for virulence. LLO is a secreted protein toxin that can be detected easily with the use of blood agar or haemolysis assays and it is well characterized and understood. This paper focuses on some of the common methods used to detect the pathogen and the LLO toxin in food products and comments on some of the potential uses and drawbacks for the food industry.

Methods for the isolation and identification of Listeria spp. and Listeria monocytogenes: a review

Listeria monocytogenes is an important food-borne pathogen and is widely tested for in food, environmental and clinical samples. Identification traditionally involved culture methods based on selective enrichment and plating followed by the characterization of Listeria spp. based on colony morphology, sugar fermentation and haemolytic properties. These methods are the gold standard; but they are lengthy and may not be suitable for testing of foods with short shelf lives. As a result more rapid tests were developed based on antibodies (ELISA) or molecular techniques (PCR or DNA hybridization). While these tests possess equal sensitivity, they are rapid and allow testing to be completed within 48 h. More recently, molecular methods were developed that target RNA rather than DNA, such as RT-PCR, real time PCR or nucleic acid based sequence amplification (NASBA). These tests not only provide a measure of cell viability but they can also be used for quantitative analysis. In addition, a variety of tests are available for sub-species characterization, which are particularly useful in epidemiological investigations. Early typing methods differentiated isolates based on phenotypic markers, such as multilocus enzyme electrophoresis, phage typing and serotyping. These phenotypic typing methods are being replaced by molecular tests, which reflect genetic relationships between isolates and are more accurate. These new methods are currently mainly used in research but their considerable potential for routine testing in the future cannot be overlooked.

Real-time nucleic acid-based detection methods for pathogenic bacteria in food

Quality assurance in the food industry in recent years has involved the acceptance and implementation of a variety of nucleic acid-based methods for rapid and sensitive detection of food-associated pathogenic bacteria. Techniques such as polymerase chain reaction have greatly expedited the process of pathogen detection and have in some cases replaced traditional methods for bacterial enumeration in food. Conventional PCR, albeit sensitive and specific under optimized conditions, obligates the user to employ agarose gel electrophoresis as the means for endpoint analysis following sample processing. For the last few years, a variety of real-time PCR chemistries and detection instruments have appeared on the market, and many of these lend themselves to applications in food microbiology. These approaches afford a user the ability to amplify DNA or RNA, as well as detect and confirm target sequence identity in a closed-tube format with the use of a variety of fluorophores, labeled probes, or both, without the need to run gels. Such real-time chemistries also offer greater sensitivity than traditional gel visualization and can be semiquantitative and multiplexed depending on the specific experimental objectives. This review emphasizes the current systems available for real-time PCR-based pathogen detection, the basic mechanisms and requirements for each, and the prospects for development over the next few years in the food industry.