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Zbrun MV, Moreno N, Camussone CM, Signorini ML, Primo ME. Comparison of real-time PCR and nested PCR based on the HlyA gene for the detection of Listeria monocytogenes. Application on cheese samples. Braz J Microbiol 2024; 55:1783-1791. [PMID: 38687417 PMCID: PMC11153442 DOI: 10.1007/s42770-024-01353-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Accepted: 04/22/2024] [Indexed: 05/02/2024] Open
Abstract
The aim of the present study was to compare the performance of a nested polymerase chain reaction (nPCR) and a real-time PCR based on the amplification of the HlyA gene from Listeria monocytogenes using a plasmid DNA standard. Nested PCR was developed with an internal amplification control (IAC). Both techniques were validated in soft cheese samples by comparing their results with the results of the microbiological reference method ISO 11290-1:2017. Cheese samples artificially contaminated with 3.5 to 3,500 UFC/25 g were processed by ISO 11290-1:2017 and, at several times of culture, DNA samples were extracted. All cheeses contaminated with L. monocytogenes were positive for the microbiological method 96 h post contamination and for nPCR and real-time PCR 48 h post contamination. At this time, the HlyA gene was amplified in all contaminated samples. Both molecular techniques showed the same sensitivity, 30 copies/reaction or 3.5 UFC/25 g, when plasmid DNA standard or artificially contaminated cheese samples were used. Finally, eighty soft cheese samples obtained from local retail stores and tested by three methods were negative, indicating a 100% concordance in results. The development of an nPCR with IAC reinforces the reliability of the negative results without increasing the costs of the reaction. Besides, nPCR showed less sensitivity to the presence of inhibitory substances in the reaction. The use of one of these molecular techniques could be easily coupled to the microbiological method, serving as a screening method in the food industry for hygiene monitoring and early identification of contaminated foods.
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Affiliation(s)
- María V Zbrun
- Instituto de Investigación de La Cadena Láctea (IdICaL) (INTA- CONICET), Ruta 34 Km 227, (2300), Rafaela, Santa Fe, Argentina
- Department of Public Health, Faculty of Veterinary Science, Litoral National University, Kreder 2805, (3080), Esperanza, Santa Fe, Argentina
| | - Nadia Moreno
- Faculty of Technology and Innovation for Development, Food Sciences Area, National University of Rafaela (UNRAf), Bv. Roca 989, (2300), Rafaela, Santa Fe, Argentina
| | - Cecilia M Camussone
- Instituto de Investigación de La Cadena Láctea (IdICaL) (INTA- CONICET), Ruta 34 Km 227, (2300), Rafaela, Santa Fe, Argentina
| | - Marcelo L Signorini
- Instituto de Investigación de La Cadena Láctea (IdICaL) (INTA- CONICET), Ruta 34 Km 227, (2300), Rafaela, Santa Fe, Argentina
- Department of Public Health, Faculty of Veterinary Science, Litoral National University, Kreder 2805, (3080), Esperanza, Santa Fe, Argentina
| | - María E Primo
- Instituto de Investigación de La Cadena Láctea (IdICaL) (INTA- CONICET), Ruta 34 Km 227, Faculty of Technology and Innovation for Development, Food Sciences Area, National University of Rafaela (UNRAf), Bv. Roca 989, (2300), Rafaela, Santa Fe, Argentina.
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Kim W, Yoon Y, Seo Y, Lee Y, Lee H, Kim S, Ha J, Choi Y, Oh H, Kim Y, Kang J, Park E, Yoo Y, Sung M, Lee S. Development of Listeria monocytogenes detection technique in mushroom based on real-time quantitative PCR through improvement of enrichment medium. FOOD SCIENCE AND TECHNOLOGY RESEARCH 2021. [DOI: 10.3136/fstr.27.837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Woori Kim
- Department of Food and Nutrition, Sookmyung Women's University
| | - Yohan Yoon
- Department of Food and Nutrition, Sookmyung Women's University
| | - Yeongeun Seo
- Department of Food and Nutrition, Sookmyung Women's University
| | - Yewon Lee
- Department of Food and Nutrition, Sookmyung Women's University
| | - Heeyoung Lee
- Food Standard Research Center, Korea Food Research Institute
| | | | | | | | - Hyemin Oh
- Department of Food and Nutrition, Sookmyung Women's University
| | - Yujin Kim
- Department of Food and Nutrition, Sookmyung Women's University
| | - Joohyun Kang
- Department of Food and Nutrition, Sookmyung Women's University
| | - Eunyoung Park
- Department of Food and Nutrition, Sookmyung Women's University
| | - Yoonjeong Yoo
- Department of Food and Nutrition, Sookmyung Women's University
| | - Miseon Sung
- Department of Food and Nutrition, Sookmyung Women's University
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Gwak SH, Kim JH, Oh SW. How to rapidly and sensitively detect for Escherichia coli O157:H7 and Salmonella Typhimurium in cabbage using filtration, DNA concentration, and real-time PCR after short-term enrichment. Lebensm Wiss Technol 2020. [DOI: 10.1016/j.lwt.2020.109840] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Aryana KJ, Olson DW. A 100-Year Review: Yogurt and other cultured dairy products. J Dairy Sci 2017; 100:9987-10013. [DOI: 10.3168/jds.2017-12981] [Citation(s) in RCA: 204] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 08/01/2017] [Indexed: 11/19/2022]
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Cho AR, Dong HJ, Seo KH, Cho S. Development of a loop-mediated isothermal amplification assay for detecting Listeria monocytogenes prfA in milk. Food Sci Biotechnol 2014. [DOI: 10.1007/s10068-014-0064-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Wang Z, Miu T, Xu H, Duan N, Ding X, Li S. Sensitive immunoassay of Listeria monocytogenes with highly fluorescent bioconjugated silica nanoparticles probe. J Microbiol Methods 2010; 83:179-84. [DOI: 10.1016/j.mimet.2010.08.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2010] [Revised: 08/13/2010] [Accepted: 08/17/2010] [Indexed: 11/24/2022]
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7
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Yu YG, Wu H, Liu YY, Li SL, Yang XQ, Xiao XL. A multipathogen selective enrichment broth for simultaneous growth ofSalmonella entericaserovar Enteritidis,Staphylococcus aureus, andListeria monocytogenes. Can J Microbiol 2010; 56:585-97. [DOI: 10.1139/w10-040] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A selective enrichment broth (SSL) was formulated to allow concurrent growth of 3 prominent food-borne pathogens: Salmonella enterica serovar Enteritidis, Staphylococcus aureus , and Listeria monocytogenes . Nalidixic acid, lithium chloride, and potassium tellurite were added as the selective agents, while sodium pyruvate and mannitol were employed as the supplemented elements. In the individual growth trial, the target pathogens were capable of growing in SSL to as high as 7–8 log10colony-forming units (CFU)/mL after 24 h incubation at 37 °C when being inoculated at 50–100 CFU/mL. In the simultaneous growth trial, the 3 combined target pathogens showed similar growth rates. The results show that SSL could support the successful simultaneous enrichment of 3 pathogens; however, SSL inhibited the growth of nontarget bacteria. In the artificial contaminated raw beef and ready-to-eat chicken, a high recovery of these 3 target pathogens was obtained in SSL. Finally, Salmonella Enteritidis, Staphylococcus aureus, and L. monocytogenes were detected from 710 suspicious food samples by SSL with real-time PCR, and no false-positive or -negative results were reported. In summary, SSL has been shown to be a suitable broth for the simultaneous detection of the 3 prominent food-borne pathogens by multipathogen detection on a single-assay platform.
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Affiliation(s)
- Yi-Gang Yu
- Institution of Food Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, P.R. China
- Heilongjiang Entry–Exit Inspection and Quarantine Bureau, Harbin 150008, P.R. China
| | - Hui Wu
- Institution of Food Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, P.R. China
- Heilongjiang Entry–Exit Inspection and Quarantine Bureau, Harbin 150008, P.R. China
| | - Yuan-Yuan Liu
- Institution of Food Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, P.R. China
- Heilongjiang Entry–Exit Inspection and Quarantine Bureau, Harbin 150008, P.R. China
| | - Su-Long Li
- Institution of Food Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, P.R. China
- Heilongjiang Entry–Exit Inspection and Quarantine Bureau, Harbin 150008, P.R. China
| | - Xiao-Quan Yang
- Institution of Food Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, P.R. China
- Heilongjiang Entry–Exit Inspection and Quarantine Bureau, Harbin 150008, P.R. China
| | - Xing-Long Xiao
- Institution of Food Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, P.R. China
- Heilongjiang Entry–Exit Inspection and Quarantine Bureau, Harbin 150008, P.R. China
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O’ Grady J, Sedano-Balbás S, Maher M, Smith T, Barry T. Rapid real-time PCR detection of Listeria monocytogenes in enriched food samples based on the ssrA gene, a novel diagnostic target. Food Microbiol 2008; 25:75-84. [DOI: 10.1016/j.fm.2007.07.007] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2007] [Revised: 07/26/2007] [Accepted: 07/29/2007] [Indexed: 11/28/2022]
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Rossmanith P, Krassnig M, Wagner M, Hein I. Detection of Listeria monocytogenes in food using a combined enrichment/real-time PCR method targeting the prfA gene. Res Microbiol 2006; 157:763-71. [PMID: 16814987 DOI: 10.1016/j.resmic.2006.03.003] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2005] [Revised: 02/15/2006] [Accepted: 03/06/2006] [Indexed: 11/23/2022]
Abstract
A combined enrichment/real-time PCR method for the detection of Listeria monocytogenes is presented. The method is based on a conventional PCR assay targeting the prfA gene, which has been validated and suggested as an international standard PCR method for identifying L. monocytogenes in food. This real-time PCR assay includes an internal amplification control. Inclusivity and exclusivity were 100% each when testing 100 L. monocytogenes isolates, 30 Listeria spp. isolates other than L. monocytogenes, and 29 non-Listeria isolates. The theoretical detection limit was one copy of the target gene per PCR reaction and the practical detection limit was about 5 copies per PCR. Using the combined enrichment/real-time PCR method, 7.5 CFU/25 ml of artificially contaminated raw milk, and 9, 1, and 1 CFU/15 g of artificially contaminated salmon, pâté, and green-veined cheese, respectively, were detected. When analyzing 76 naturally contaminated food samples of various types and comparing the results with the ISO 11290-1 standard method, the relative accuracy was 96%, the relative specificity 100%, and the relative sensitivity, 76.9%.
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Affiliation(s)
- Peter Rossmanith
- Institute of Milk Hygiene, Milk Technology, and Food Science, Department of Veterinary Public Health and Food Science, University of Veterinary Medicine, Veterinärplatz 1, 1210 Vienna, Austria
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Churchill RLT, Lee H, Hall JC. Detection of Listeria monocytogenes and the toxin listeriolysin O in food. J Microbiol Methods 2005; 64:141-70. [PMID: 16310269 DOI: 10.1016/j.mimet.2005.10.007] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Revised: 10/14/2005] [Accepted: 10/14/2005] [Indexed: 10/25/2022]
Abstract
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.
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Affiliation(s)
- Robin L T Churchill
- Department of Environmental Biology, University of Guelph, Guelph, ON, Canada
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Hein I, Jørgensen HJ, Loncarevic S, Wagner M. Quantification of Staphylococcus aureus in unpasteurised bovine and caprine milk by real-time PCR. Res Microbiol 2005; 156:554-63. [PMID: 15862454 DOI: 10.1016/j.resmic.2005.01.003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Revised: 09/14/2004] [Accepted: 01/05/2005] [Indexed: 12/01/2022]
Abstract
A sensitive and reproducible real-time PCR assay targeting the nuc gene of Staphylococcus aureus was applied for quantification of this microorganism in artificially and naturally contaminated raw milk samples. The S. aureus cell equivalents (SCEs) estimated by the real-time PCR method were two log scales higher than colony forming units (CFUs) estimated from a plate count method in artificially contaminated milk. The repeatability of the real-time PCR assay including the DNA isolation procedure was assessed by analysing the data derived from naturally contaminated samples. The relative standard deviation of the log-transformed data of four real-time PCR measurements including duplicate DNA isolations ranged between 11.3 and 1.0%. When analysing 80 bovine and 107 caprine naturally contaminated raw milk samples, the real-time PCR method yielded 19.3% more positive samples than the plate count method. With the exception of one sample, SCEs were always higher than CFUs. The difference between SCEs and CFUs was highly variable, and it was not possible to correlate real-time PCR-derived SCEs and CFUs. However, as each SCE detected by real-time PCR indicates a S. aureus cell, which is or has been present in the sample, this method offers the advantage of a retrospective analysis even of processed samples to aid food poisoning-related risk assessment.
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Affiliation(s)
- Ingeborg Hein
- Institute for Milk Hygiene, Milk Technology, and Food Science, University for Veterinary Medicine, Veterinärplatz 1, 1210 Vienna, Austria.
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Luo H, Yousef AE, Wang HH. A real-time polymerase chain reaction-based method for rapid and specific detection of spoilage Alicyclobacillus spp. in apple juice. Lett Appl Microbiol 2004; 39:376-82. [PMID: 15355542 DOI: 10.1111/j.1472-765x.2004.01596.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIMS To develop a real-time PCR-based rapid detection method for spoilage Alicyclobacillus spp. in juice products. METHODS AND RESULTS The squalene-hopene cyclase-encoding gene was targeted for primer-and-probe development. Gene fragments from representative strains were cloned, and PCR primers and probe were designed by DNA sequence comparison. Selected bacteria were examined for cross-reactivity by the new method. Cells were serially diluted in apple juice and saline, and examined by the new method to establish detection sensitivity. Using the newly developed Taqman real-time PCR-based method, strains of Alicyclobacillus acidocaldarius and A. acidoterrestris were detected without cross reactivity with other common food-borne micro-organisms. Detection of <10 cells per PCR reaction from juice samples was accomplished within 3-5 h. CONCLUSION This is the first reported real-time PCR-based detection method for Alicyclobacillus spp. and its application in juice products is demonstrated. SIGNIFICANCE AND IMPACT OF THE STUDY As a favourable alternative for the laborious and time-consuming culture- or biochemical characterization-based techniques, the system has great potential for industrial applications from raw material screening to final product quality control.
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Affiliation(s)
- H Luo
- Department of Food Science and Technology, The Ohio State University, Columbus, OH 43210, USA
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Detection of Listeria monocytogenes in food, equivalent to EN ISO 11290-1 or ISO 10560, by a three-days polymerase chain reaction-based method. Food Control 2003. [DOI: 10.1016/s0956-7135(02)00085-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Koo K, Jaykus LA. Detection of Listeria monocytogenes from a model food by fluorescence resonance energy transfer-based PCR with an asymmetric fluorogenic probe set. Appl Environ Microbiol 2003; 69:1082-8. [PMID: 12571032 PMCID: PMC143584 DOI: 10.1128/aem.69.2.1082-1088.2003] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
It has been shown that fluorescence resonance energy transfer (FRET)-based PCR, including the TaqMan assay and molecular beacons, has potential for rapid detection of pathogens. In these promising real-time detection assays a single internal oligonucleotide probe labeled on both the 5' (reporter) and 3' (quencher) ends is used for selective generation of fluorescence. In this paper, we describe the use of a previously reported novel probe design for FRET-based PCR detection of Listeria monocytogenes in pure culture and in a model food commodity. In the assay described here an asymmetric probe set is used; this probe set consists of a long 5' fluorescein-labeled reporter probe and a short, complementary 3' DABCYL-labeled quencher oligonucleotide, which are used in a 5' nuclease amplification and detection assay. By using the listeriolysin O (hly) and p60 (iap) genes as amplification targets, the performance of two primer-probe sets in amplification and subsequent detection of target DNA was evaluated. In studies performed with pure cultures of L. monocytogenes, the PCR profiles indicated that the relative change in fluorescence intensity was correlated with both the initial number of cells and the accumulation of specific amplicons for both hly and iap gene fragments. Experiments were also done to determine the applicability of the method to the detection of L. monocytogenes by targeting hly DNA and its short-lived mRNA product in a model food commodity. Twenty-five-milliliter samples of reconstituted nonfat dry milk (NFDM) were seeded with L. monocytogenes and processed to concentrate the bacteria by centrifugation, and this was followed by nucleic acid extraction and amplification with hly-specific primers. Endpoint detection of PCR and reverse transcription-PCR amplicons could be achieved at inoculum levels of 10(3) and 10(4) CFU of L. monocytogenes/25 ml of NFDM, respectively. This study demonstrated that this asymmetric FRET-based amplification and detection protocol provides an alternative approach for endpoint detection of nucleic acid amplification products as applied to detection of pathogens in a model food.
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Affiliation(s)
- Kai Koo
- Department of Food Science, College of Life Science and Agriculture, North Carolina State University, and Southeast Dairy Foods Research Center, Raleigh, North Carolina 27695-7624, USA
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Frahm E, Obst U. Application of the fluorogenic probe technique (TaqMan PCR) to the detection of Enterococcus spp. and Escherichia coli in water samples. J Microbiol Methods 2003; 52:123-31. [PMID: 12401234 DOI: 10.1016/s0167-7012(02)00150-1] [Citation(s) in RCA: 174] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
A recent PCR detection technique (TaqMan) based on the 5'-3'-exonuclease activity of the Taq DNA polymerase was applied to the detection of indicator organisms in water samples. In this technique, an increasing fluorescence signal is measured online which enables direct assessment of results after PCR without additional detection steps. The test is completed within about 5 h. Two sets of primers and probes were designed and tested: a genus-specific assay for the detection of Enterococcus spp. based on 23S rRNA sequence and an Escherichia coli-specific assay based on the uidA gene sequence. Specificity of the assays was confirmed by testing strains of target bacteria and potential interfering microorganisms. Application of the tests to 55 natural water samples showed the need of an overnight enrichment step to achieve compliance with detection limits of existing regulations. Compared with a parallel microbiological examination of the samples, agreement was 96% with the Enterococcus assay and 98% with the E. coli assay. The rapidity and feasibility of the method point to benefits in drinking water analysis, particularly in emergency situations and, thus, to improved public health management.
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Affiliation(s)
- Edith Frahm
- Forschungszentrum Karlsruhe GmbH, ITC-WGT, Abt. Umweltmikrobiologie, PF 3640, D-76021 Karlsruhe, Germany.
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Hough AJ, Harbison SA, Savill MG, Melton LD, Fletcher G. Rapid enumeration of Listeria monocytogenes in artificially contaminated cabbage using real-time polymerase chain reaction. J Food Prot 2002; 65:1329-32. [PMID: 12182489 DOI: 10.4315/0362-028x-65.8.1329] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A quantitative real-time polymerase chain reaction (PCR) detection method specific for Listeria monocytogenes was developed, and studies involving pure culture showed that the response of the assay was linear over 7 log10 (log) cycles. The method was then applied to the detection of L. monocytogenes artificially inoculated onto cabbage, a vegetable chosen because it is a major component of coleslaw, which has been associated with an outbreak of listeriosis. After being allowed to attach to the food, cells were washed from the cabbage leaf surface and recovered by centrifugation. The DNA was purified by an organic solvent extraction technique and analyzed by real-time PCR. In this matrix, the method again produced a linear response over 7 log cycles from 1.4 x 10(2) to 1.4 x 10(9) CFU of L. monocytogenes in 25 g of cabbage, and analysis of the reproducibility of the system showed that log differences in L. monocytogenes numbers added to cabbage could be reliably distinguished. The system allowed quantitative results to be obtained within 8 h and was relatively inexpensive, showing good potential for routine analytical use.
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Affiliation(s)
- Angela J Hough
- Christchurch Science Centre, Institute of Environmental Science and Research, New Zealand.
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Hudson JA, Lake RJ, Savill MG, Scholes P, McCormick RE. Rapid detection of Listeria monocytogenes in ham samples using immunomagnetic separation followed by polymerase chain reaction. J Appl Microbiol 2001; 90:614-21. [PMID: 11309074 DOI: 10.1046/j.1365-2672.2001.01287.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIMS To develop a 24-h system for the detection of Listeria monocytogenes in ham. METHODS AND RESULTS An immunomagnetic separation (IMS) of bacteria directly from ham followed by extraction of DNA and detection using a new multiplex polymerase chain reaction (PCR) was used. The PCR method used one primer pair targeted at the listeriolysin O gene of L. monocytogenes and the other pair for a region of the 23S rRNA genes of Listeria, giving products of 706 and 239 bp, respectively. The combined IMS/PCR was calculated to be capable of detecting as few as 1.1 L. monocytogenes cells g-1 in a 25-g ham sample. CONCLUSION The process produced acceptable results, but the IMS step is the main barrier to further improvement of sensitivity. The DNA isolation was the most time-consuming step in the process. SIGNIFICANCE AND IMPACT OF THE STUDY A 24-h test for the presence of L. monocytogenes will be useful to the food industry and significantly assist in the timely investigation of outbreaks.
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Affiliation(s)
- J A Hudson
- Institute of Environmental Science and Research (ESR) Ltd, Christchurch Science Centre, PO Box 29-181, Ilam, Christchurch, New Zealand.
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Hein I, Klein D, Lehner A, Bubert A, Brandl E, Wagner M. Detection and quantification of the iap gene of Listeria monocytogenes and Listeria innocua by a new real-time quantitative PCR assay. Res Microbiol 2001; 152:37-46. [PMID: 11281324 DOI: 10.1016/s0923-2508(00)01166-9] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A real-time quantitative polymerase chain reaction (PCR) assay for direct detection and enumeration of Listeria monocytogenes and Listeria innocua was developed and applied to artificially contaminated milk samples. The iap gene present in both species was used as a target for amplification of a 175-bp (L. monocytogenes) and a 309-bp (L. innocua) fragment. To ensure that L. monocytogenes and L. innocua are specifically detectable, tests were carried out using 42 L. monocytogenes strains and 33 L. innocua strains belonging to different serovars. Specificity was also confirmed using 22 bacterial strains not belonging to the genus Listeria, including closely related bacteria. In addition to specificity, the reported assay is characterized by a wide dynamic range of quantification and a high sensitivity, as we could detect as few as six copies of the iap gene per PCR using purified DNA as template. When applied to direct detection and quantification of L. monocytogenes in milk, the more rapid real-time quantitative PCR assay was as sensitive as the traditional plate count method, but real-time quantitative PCR-derived iap gene copy numbers were one to two logs higher than colony-forming units obtained by the plate count method.
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Affiliation(s)
- I Hein
- Institute of Milk Hygiene, Milk Technology and Food Science, University of Veterinary Medicine, Vienna, Austria.
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