Recent Advances in the Detection of Listeria monocytogenes

Listeria monocytogenes is the third-most severe pathogen causing a yearly outbreak of food poisoning in the world that proliferates widely in the environment. Infants, pregnant mothers, and immuno-compromised people are at high risk. Its ability to grow in both biotic and abiotic environments leads to epidemics that infect 5 out of 10 people annually. Because of the epithelial adhesion (by E-cadherin binding), it can suppress immune cells and thrive in the gastrointestinal tract till the brain through blood flow (E-cadherin). Microbial culture is still used as a gold standard, but takes a long time and often yields false positive results due to incompetence and temperature variations. Therefore, in order to treat it rather than using broad spectrum antibiotics, a standardized time-saving and highly specific technology for early detection is very important. It has been observed that the production of a particular antibody is delaying (so does the detection process) as a result of the inadequate understanding of the pathophysiology of the bacteria. This book chapter provides a brief summary of a pathogen as well as the scientific advances that led to its identification more easily.

Detection of Escherichia coli in Food Samples Using Culture and Polymerase Chain Reaction Methods

Methods for the rapid detection of Escherichia coli and its related toxins are key to minimizing the risk of exposure to foodborne pathogens. The present study aimed to detect E. coli in food specimens using culture and polymerase chain reaction (PCR) techniques. One hundred and fifty samples from different types of food, comprising beef (n=60), chicken (n=72), and fish (n=18), were analyzed for the identification of E. coli by conventional and PCR methods. The results showed that out of 150 food samples, 44 (29.3%) were positive by culture, and 50 (33.3%) were positive by PCR. Significant differences were detected between sample types with culture (p-value < 0.005). When culture was considered the gold standard, the sensitivity of PCR was 100%, while the specificity was 94.34%. The six-hour pre-enrichment and PCR analysis are reliable in fast detection of E. coli in food samples. Hence, the identification of food pathogens using molecular-based methods would become more useful in routine diagnostic laboratories.

Vancomycin-dendrimer based multivalent magnetic separation nanoplatforms combined with multiplex quantitative PCR assay for detecting pathogenic bacteria in human blood

Sepsis caused by bacteria has high morbidity and mortality, and it is neccerssay to establish a fast, convenient, and facility assays for detection of bacteria. In this study, we have developed established a simple, rapid, and ultrasensitive vancomycin (Van) and dendrimer nanoparticles-based method to isolate and detect bacteria in human blood using a multivalent binding strategy. The proposed Bio-den-Van multivalent capture nanoplatform combined with m-qPCR for simultaneous detection of two kinds of bacteria was demonstrated with rapid 2 min bacteria isolation with a linear range at 3.2 × 10¹-3.2 × 10⁶ CFU·mL^-1 for L. monocytogenes and 4.1 × 10¹-4.1 × 10⁶ CFU·mL^-1 for S. aureus, respectively. The limit of detection (LOD) for simultaneous detection of L. monocytogenes and S. aureus were 32 and 41 CFU·mL^-1 in spiked human blood samples, respectively. Other bacteria had an insignificant interference with the test results. This Bio-den-Van multivalent capture nanoplatform combined with m-qPCR detection exhibited rapid, high sensitivity and specificity in simultaneous detection of various bacteria. To our knowledge, this is the first time that Bio-den-Van multivalent capture nanoplatform was used with Van as a recognition molecule for the simultaneous capture and subsequent detection of two bacteria from spiked human blood sample. This method holds great potential for future clinical applications.

Enhancing the antibacterial activity of PMAP-37 by increasing its hydrophobicity

With increasing resistance against conventional antibiotics, there is an urgent need to discover novel substances to replace antibiotics. This need provides an opportunity for the development of antimicrobial peptides (AMPs). To develop new AMPs with effective and safe therapeutic effects, two PMAP-37 analogs called PMAP-37(R13-I) and PMAP-37(K20/27-I) were designed to increase hydrophobicity. Antimicrobial susceptibility testing and animal infection models were used to assess their antibacterial activity. The results showed that the minimal inhibitory concentrations of PMAP-37(R13-I) were lower than those of PMAP-37 for two gram-negative strains. Compared with PMAP-37, PMAP-37(K20/27-I) not only inhibited the growth of most bacterial strains, but also exhibited antibacterial activity against Shigella flexneri CICC21534. In addition, PMAP-37(K20/27-I) exhibited pH and thermal stability. PMAP-37(R13-I) had a therapeutic effect only in mice infected with Salmonella typhimurium SL1344. However, PMAP-37(K20/27-I) exhibited the therapeutic effects, whether in the clinical symptoms, the tissue lesions, or the tissue bacterial loads and the survival rates in mice infected with Staphylococcus aureus ATCC25923 or S. typhimurium SL1344. Therefore, PMAP-37(K20/27-I) can be used as a substitute for antibiotics against infection with bacterial strains.

Rapid Colorimetric Assay for Detection of Listeria monocytogenes in Food Samples Using LAMP Formation of DNA Concatemers and Gold Nanoparticle-DNA Probe Complex

Listeria monocytogenes is a major foodborne pathogen of global health concern. Herein, the rapid diagnosis of L. monocytogenes has been achieved using loop-mediated isothermal amplification (LAMP) based on the phosphatidylcholine-phospholipase C gene (plcB). Colorimetric detection was then performed through the formation of DNA concatemers and a gold nanoparticle/DNA probe complex (GNP/DNA probe). The overall detection process was accomplished within approximately 1 h with no need for complicated equipment. The limits of detection for L. monocytogenes in the forms of purified genomic DNA and pure culture were 800 fg and 2.82 CFU mL⁻¹, respectively. No cross reactions were observed from closely related bacteria species. The LAMP-GNP/DNA probe assay was applied to the detection of 200 raw chicken meat samples and compared to routine standard methods. The data revealed that the specificity, sensitivity, and accuracy were 100, 90.20, and 97.50%, respectively. The present assay was 100% in conformity with LAMP-agarose gel electrophoresis assay. Five samples that were negative by both assays appeared to have the pathogen at below the level of detection. The assay can be applied as a rapid direct screening method for L. monocytogenes.

Multiplex PCR for simultaneous identification of E. coli O157:H7, Salmonella spp. and L. monocytogenes in food

The rapid detection of pathogens in food is becoming increasingly critical for ensuring the safety of consumers, since the majority of food-borne illnesses and deaths are caused by pathogenic bacteria. Hence, rapid, sensitive, inexpensive and convenient approaches to detect food-borne pathogenic bacteria is essential in controlling food safety. In this study, a multiplex PCR assay for the rapid and simultaneous detection of Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes was established. The invA, stx and hlyA genes specifically amplified DNA fragments of 284, 404 and 510 bp from Salmonella spp., L. monocytogenes and E. coli O157:H7, respectively. The 16S rRNA gene was targeted as an internal control gene in the presence of bacterial DNA. The specificity and sensitivity of the multiplex PCR were performed by testing different strains. The multiplex PCR assay was able to specifically simultaneously detect ten colony-forming unit/mL of each pathogen in artificially inoculated samples after enrichment for 12 h. The whole process took less than 24 h to complete, indicating that the assay is suitable for reliable and rapid identification of these three food-borne pathogens, which could be suitable in microbial epidemiology investigation.

An insight into the isolation, enumeration, and molecular detection of Listeria monocytogenes in food

Listeria monocytogenes, a foodborne pathogen that can cause listeriosis through the consumption of food contaminated with this pathogen. The ability of L. monocytogenes to survive in extreme conditions and cause food contaminations have become a major concern. Hence, routine microbiological food testing is necessary to prevent food contamination and outbreaks of foodborne illness. This review provides insight into the methods for cultural detection, enumeration, and molecular identification of L. monocytogenes in various food samples. There are a number of enrichment and plating media that can be used for the isolation of L. monocytogenes from food samples. Enrichment media such as buffered Listeria enrichment broth, Fraser broth, and University of Vermont Medium (UVM) Listeria enrichment broth are recommended by regulatory agencies such as Food and Drug Administration-bacteriological and analytical method (FDA-BAM), US Department of Agriculture-Food and Safety (USDA-FSIS), and International Organization for Standardization (ISO). Many plating media are available for the isolation of L. monocytogenes, for instance, polymyxin acriflavin lithium-chloride ceftazidime aesculin mannitol, Oxford, and other chromogenic media. Besides, reference methods like FDA-BAM, ISO 11290 method, and USDA-FSIS method are usually applied for the cultural detection or enumeration of L. monocytogenes. most probable number technique is applied for the enumeration of L. monocytogenes in the case of low level contamination. Molecular methods including polymerase chain reaction, multiplex polymerase chain reaction, real-time/quantitative polymerase chain reaction, nucleic acid sequence-based amplification, loop-mediated isothermal amplification, DNA microarray, and next generation sequencing technology for the detection and identification of L. monocytogenes are discussed in this review. Overall, molecular methods are rapid, sensitive, specific, time- and labor-saving. In future, there are chances for the development of new techniques for the detection and identification of foodborne with improved features.

A multiplex PCR assay for simultaneous detection of Escherichia coli O157:H7, Bacillus cereus, Vibrio parahaemolyticus, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus in Korean ready-to-eat food

A multiplex polymerase chain reaction (PCR) assay was developed for simultaneous detection of Escherichia coli O157:H7, Bacillus cereus, Vibrio parahaemolyticus, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus in various Korean ready-to-eat foods. The six specific primer pairs for multiplex PCR were selected based on the O157 antigen (rfbE) gene of E. coli O157:H7, the DNA gyrase subunit B (gyrB) gene of B. cereus, the toxin regulatory protein (toxR) gene of V. parahaemolyticus, the invasion protein A (invA) gene of Salmonella spp., the hemolysin (hly) gene of L. monocytogenes, and the thermonuclease (nuc) gene of S. aureus. The 16S rRNA gene was targeted as an internal control gene in the presence of bacterial DNA. The specificity and sensitivity assays for multiplex primer pairs were investigated by testing different strains. When this multiplex PCR assay was applied to evaluate the validity of detecting six foodborne pathogens in artificially inoculated several ready-to-eat food samples, the assay was able to specifically simultaneously detect as few as 1 colony-forming unit/mL of each pathogen after enrichment for 12 h. Their presence in naturally contaminated samples also indicates that the developed multiplex PCR assay is an effective and informative supplement for practical use.

In-house validation of a multiplex real-time PCR method for simultaneous detection of Salmonella spp., Escherichia coli O157 and Listeria monocytogenes

A wide variety of qPCR methods currently exist for Salmonella spp., Escherichia coli O157 and Listeria monocytogenes detection. These methods target several genes and use different detection chemistries, either in simplex or in multiplex formats. However, the majority of these methods have not been carefully validated, and the number of validated methods that use multiplex qPCR is even lower. The aim of the present study was to develop and validate a multiplex qPCR method from previously validated simplex qPCR primers and probes. A modified broth medium was selected and primary and secondary enrichment times were further optimized. Efficiency of the newly combined qPCR system was comprised between 91% and 108%, for simplex and multiplex analyses. A total of 152 food and environmental, natural and spiked samples, were analyzed for the evaluation of the method obtaining values above 91% that were reached for all the quality parameters analyzed. A very low limit of detection (5 cfu/25 g after enrichment) for simultaneous identification of these 3 pathogens was obtained.

In-situ immuno-gold nanoparticle network ELISA biosensors for pathogen detection

Food poisoning microorganisms that contaminate food products and compromise food safety and security have been considered a major health threat and a serious concern for food producers and processors. Developing sensor technologies that are rapid for sensitive and selective detection and quantification of pathogens is a high priority for scientists in academia, state and federal research institutes, and industries. In this work we propose an in-situ immuno-AuNP network-based ELISA biosensor integrated with a sample concentration step based on immuno-magnetic separation to detect pathogenic microorganisms with high sensitivity. The sensor system was optimized by the specific formation of immuno-AuNP network onto the antigenic site present at the outer membrane surface of bacteria and the analytical concept was validated by a microtiter immunoassay. The in-situ network biosensor was able to detect pathogens at extremely low numbers: 3 cells/mL of Escherichia coli O157:H7 and Salmonella typhimurium in buffer and 3 CFU/mL of E. coli O157:H7 and 15CFU/mL of S. typhimurium in real sample conditions within 2h of inoculation. The ability to monitor target bacteria with improved analytical sensitivity compared to the current techniques presents a unique opportunity for routine monitoring to improve the safety of foods.

Methods used for the detection and subtyping of Listeria monocytogenes

Listeria monocytogenes is an important foodborne pathogen responsible for non-invasive and invasive diseases in the elderly, pregnant women, neonates and immunocompromised populations. This bacterium has many similarities with other non-pathogenic Listeria species which makes its detection from food and environmental samples challenging. Subtyping of L. monocytogenes strains can prove to be crucial in epidemiological investigations, source tracking contamination from food processing plants and determining evolutionary relationships between different strains. In recent years there has been a shift towards the use of molecular subtyping. This has led to the development of new subtyping techniques such as multi-locus variable number tandem repeat analysis (MLVA) and multi-locus sequence based typing (MLST). This review focuses on the available methods for Listeria detection including immuno-based techniques and the more recently developed molecular methods and analytical techniques such as matrix-assisted laser desorption/ionisation time-of-flight based mass spectrometry (MALDI-TOF MS). It also includes a comparison and critical analysis of the available phenotypic and genotypic subtyping techniques that have been investigated for L. monocytogenes.

Biotechnologies for the management of genetic resources for food and agriculture

In recent years, the land area under agriculture has declined as also has the rate of growth in agricultural productivity while the demand for food continues to escalate. The world population now stands at 7 billion and is expected to reach 9 billion in 2045. A broad range of agricultural genetic diversity needs to be available and utilized in order to feed this growing population. Climate change is an added threat to biodiversity that will significantly impact genetic resources for food and agriculture (GRFA) and food production. There is no simple, all-encompassing solution to the challenges of increasing productivity while conserving genetic diversity. Sustainable management of GRFA requires a multipronged approach, and as outlined in the paper, biotechnologies can provide powerful tools for the management of GRFA. These tools vary in complexity from those that are relatively simple to those that are more sophisticated. Further, advances in biotechnologies are occurring at a rapid pace and provide novel opportunities for more effective and efficient management of GRFA. Biotechnology applications must be integrated with ongoing conventional breeding and development programs in order to succeed. Additionally, the generation, adaptation, and adoption of biotechnologies require a consistent level of financial and human resources and appropriate policies need to be in place. These issues were also recognized by Member States at the FAO international technical conference on Agricultural Biotechnologies for Developing Countries (ABDC-10), which took place in March 2010 in Mexico. At the end of the conference, the Member States reached a number of key conclusions, agreeing, inter alia, that developing countries should significantly increase sustained investments in capacity building and the development and use of biotechnologies to maintain the natural resource base; that effective and enabling national biotechnology policies and science-based regulatory frameworks can facilitate the development and appropriate use of biotechnologies in developing countries; and that FAO and other relevant international organizations and donors should significantly increase their efforts to support the strengthening of national capacities in the development and appropriate use of pro-poor agricultural biotechnologies.