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Al-Awwal N, Masjedi M, El-Dweik M, Anderson SH, Ansari J. Nanoparticle immuno-fluorescent probes as a method for detection of viable E. coli O157:H7. METHODS IN MICROBIOLOGY 2022; 193:106403. [PMID: 34990644 DOI: 10.1016/j.mimet.2021.106403] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Revised: 12/22/2021] [Accepted: 12/29/2021] [Indexed: 12/17/2022]
Abstract
Development of revolutionary sensitive biosensors for detecting the presence of harmful biological species in the environment is a necessity for countering disease outbreaks. This work examined the interaction of fluorescence-labeled antibody on amine functionalized gold nanoparticles (GNP) as a model system. The synthesized tetramethylrhodamine isothiocyanate (TRITC) labeled antibody-amine functionalized GNP interaction was characterized using UV-Vis spectroscopy and Fluorescent Microscopy imaging. Transmission Electron Microscopy (TEM) was also used to observe the morphology of the GNP. In contrast to TEM, the fluorescence microscopy imaging revealed the coating of the TRITC labeled antibody on the surface of the GNP. The signals were measured using a Photon Technology Inc. fluorometer at excitation of 541 nm and emission at 555 nm to 650 nm. Tests were conducted at near real-time with results obtained using the biosensor assay within 5 min. Results indicated that there was a shift of the wavelength from lower to higher wavelength (blue to red shift) when conjugated GNP (anti-E. coliO157:H7; IgY-TRITC-GNP) are compared to free GNP, a difference of about 28 nm. The GNP demonstrated a quenching capability when compared to the TRITC labeled antibody (degree of labeling of 15.41 mol dye per mole of IgY) using fluorometer. The lower and upper detection range of this method was found to be 103-105 CFU/mL with observed fluorescence of about 42,000 counts per seconds as against 24,000 counts per seconds that was observed when the specificity of the sensor was tested using Salmonella enterica.
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Affiliation(s)
- Nasruddeen Al-Awwal
- School of Natural Resources, University of Missouri Columbia, 321 Anheuser-Busch Natural Resources Building, 65211, United States
| | - Mehdi Masjedi
- Cooperative Research and Extension, College of Agriculture, Environmental and Human Sciences, Lincoln University Missouri, 65101, United States
| | - Majed El-Dweik
- Cooperative Research and Extension, College of Agriculture, Environmental and Human Sciences, Lincoln University Missouri, 65101, United States.
| | - Stephen H Anderson
- School of Natural Resources, University of Missouri Columbia, 321 Anheuser-Busch Natural Resources Building, 65211, United States
| | - Jamshid Ansari
- School of Natural Resources, University of Missouri Columbia, 321 Anheuser-Busch Natural Resources Building, 65211, United States
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Barizuddin S, Balakrishnan B, Stringer RC, Dweik M. Highly specific and rapid immuno-fluorescent visualization and detection of E. coli O104:H4 with protein-A coated magnetic beads based LST-MUG assay. J Microbiol Methods 2015; 115:27-33. [DOI: 10.1016/j.mimet.2015.05.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 05/18/2015] [Accepted: 05/18/2015] [Indexed: 10/23/2022]
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3
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Chandrashekhar KM, Isloor S, Veeresh BH, Hegde R, Rathnamma D, Murag S, Veeregowda BM, Upendra HA, Hegde NR. Limit of detection of genomic DNA by conventional PCR for estimating the load of Staphylococcus aureus and Escherichia coli associated with bovine mastitis. Folia Microbiol (Praha) 2015; 60:465-72. [PMID: 25773783 DOI: 10.1007/s12223-015-0384-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 03/02/2015] [Indexed: 01/15/2023]
Abstract
Detection of mastitis-associated bacteria can be accomplished by culturing or by molecular techniques. On the other hand, rapid and inexpensive methods to enumerate bacterial load without culturing can be better achieved by molecular methods. Staphylococcus aureus and Escherichia coli are the predominant bacterial pathogens associated with bovine mastitis. Here, we describe the application of conventional PCR for the limit of detection (LOD) of genomic DNA of S. aureus and E. coli based on single-copy genes. The selected genes were thermonuclease (nuc), aureolysin (aur), and staphopain A (scpA) for S. aureus and β-D-glucuronidase A (uidA), cytochrome d oxidase (cyd), and rodA (a gene affecting cell shape and methicillin sensitivity) for E. coli. The LOD was 5.3, 15.9, and 143 pg for aur, nuc, and scpA genes, corresponding to S. aureus genomic copies of 1.75 × 10(3), 5.16 × 10(3), and 4.71 × 10(4), respectively. The LOD was 0.45, 12.3 and 109 pg for uidA, rodA and cyd genes, corresponding to E. coli genome copies of 8.91 × 10(1), 2.43 × 10(3), and 2.16 × 10(4), respectively. Application of uidA and aur PCRs to field strains revealed that as low as approximately 100 genome copies of E. coli and 1000-10,000 copies of S. aureus could be detected. This study is the first to report LOD of genomic DNA using conventional PCR for aur and scpA genes of S. aureus, and rodA and cyd genes of E. coli. The results should be useful for developing assays to assess bacterial load in milk and to determine the load that contributes to subclinical or clinical mastitis.
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Affiliation(s)
- K M Chandrashekhar
- Department of Microbiology, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - Shrikrishna Isloor
- Department of Microbiology, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - B H Veeresh
- Department of Microbiology, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - Raveendra Hegde
- Institute of Animal Health and Veterinary Biologicals, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - D Rathnamma
- Department of Microbiology, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - Shivaraj Murag
- Institute of Animal Health and Veterinary Biologicals, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - B M Veeregowda
- Department of Microbiology, Karnataka Veterinary Animal and Fisheries Sciences University, Hebbal, Bengaluru, 560024, India
| | - H A Upendra
- Institute of Wildlife Veterinary Research, Kudige, Kodagu, 571232, India
| | - Nagendra R Hegde
- Ella Foundation, Genome Valley, Turkapally, Shameerpet Mandal, Hyderabad, 500078, India.
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Arcobacter Species. Food Saf (Tokyo) 2015. [DOI: 10.1016/b978-0-12-800245-2.00012-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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5
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Caine LA, Nwodo UU, Okoh AI, Ndip RN, Green E. Occurrence of virulence genes associated with diarrheagenic Escherichia coli isolated from raw cow's milk from two commercial dairy farms in the Eastern Cape Province, South Africa. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2014; 11:11950-63. [PMID: 25411727 PMCID: PMC4245653 DOI: 10.3390/ijerph111111950] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 11/05/2014] [Accepted: 11/10/2014] [Indexed: 01/22/2023]
Abstract
Escherichia coli remains a public health concern worldwide as an organism that causes diarrhea and its reservoir in raw milk may play an important role in the survival and transport of pathogenic strains. Diarrheagenic E. coli strains are diverse food-borne pathogens and causes diarrhea with varying virulence in humans. We investigated the prevalence of pathogenic E. coli in raw milk from two commercial dairy farms. Four hundred raw milk samples, 200 from each dairy farm, were screened for the presence of fliCH7, eagR, ial, eagg, lt, and papC genes. In dairy farm A, 100 E. coli were identified based on culture, oxidase and Gram staining, while 88 isolates from dairy farm B were identified in the same manner. Gene detection showed fliCH7 27 (54%) to be the highest gene detected from farm A and lt 2 (4%) to be the lowest. The highest gene detected in dairy farm B was fliCH7 16 (43.2%) and papC 1 (2.7%) was the least. The amplification of pathogenic genes associated with diarrheagenic E. coli from cows' raw milk demonstrates that potentially virulent E. coli strains are widely distributed in raw milk and may be a cause of concern for human health.
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Affiliation(s)
- Lesley-Anne Caine
- Departments of Biochemistry and Microbiology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.
| | - Uchechukwu U Nwodo
- Departments of Biochemistry and Microbiology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.
| | - Anthony I Okoh
- Departments of Biochemistry and Microbiology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.
| | - Roland N Ndip
- Departments of Biochemistry and Microbiology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.
| | - Ezekiel Green
- Departments of Biochemistry and Microbiology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.
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Kirsch KR, Taylor TM, Griffin D, Castillo A, Marx DB, Smith L. Growth of Shiga toxin-producing Escherichia coli (STEC) and impacts of chilling and post-inoculation storage on STEC attachment to beef surfaces. Food Microbiol 2014; 44:236-42. [PMID: 25084668 DOI: 10.1016/j.fm.2014.06.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 06/13/2014] [Accepted: 06/16/2014] [Indexed: 11/15/2022]
Abstract
Concern has been expressed surrounding the utility of studies describing the efficacy of antimicrobial interventions targeting the Shiga toxin-producing Escherichia coli (STEC) that inoculate chilled versus non-chilled beef carcasses. The objectives of this study were to evaluate the effects of chilling (non-chilled, chilled to surface temperature of ≤5 °C) on STEC attachment to brisket surfaces, and the effects of post-inoculation storage on STEC recovery. Paired briskets from split carcasses were separated; one brisket from each pair was kept non-chilled, while the other was chilled to a surface temperature of ≤5 °C prior to inoculation. Briskets were inoculated with a cocktail of eight STEC and then stored at 5 or 25 °C. At 0, 30, 60, 90 and 120 min post-inoculation, 30 cm(2) of tissue was aseptically excised, followed by selective enumeration of strongly and loosely attached STEC. A significant, though small (0.4 log10 CFU/cm(2)), difference in the numbers of strongly attached cells was observed between non-chilled and chilled briskets (p < 0.05). Significant effects on cell attachment by the interaction of chilling and post-inoculation storage period, or chilling and post-inoculation storage temperature, were identified (p < 0.05). Results indicate beef chilling and post-inoculation storage conditions influenced STEC attachment to beef.
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Affiliation(s)
- Katie R Kirsch
- Department of Nutrition and Food Science, Texas A&M University, College Station, TX 77843-2253, USA
| | - T Matthew Taylor
- Department of Animal Science, Texas A&M AgriLife Research, College Station, TX 77843-2471, USA.
| | - Davey Griffin
- Department of Animal Science, Texas A&M AgriLife Extension, College Station, TX 77843-2471, USA
| | - Alejandro Castillo
- Department of Animal Science, Texas A&M AgriLife Research, College Station, TX 77843-2471, USA
| | - David B Marx
- Department of Statistics, University of Nebraska, Lincoln, NE 68588, USA
| | - Lynette Smith
- Department of Statistics, University of Nebraska, Lincoln, NE 68588, USA
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Vimont A, Vernozy-Rozand C, Montet MP, Lazizzera C, Bavai C, Delignette-Muller ML. Modeling and predicting the simultaneous growth of Escherichia coli O157:H7 and ground beef background microflora for various enrichment protocols. Appl Environ Microbiol 2006; 72:261-8. [PMID: 16391052 PMCID: PMC1352195 DOI: 10.1128/aem.72.1.261-268.2006] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Accepted: 09/25/2005] [Indexed: 11/20/2022] Open
Abstract
The simultaneous growth of Escherichia coli O157:H7 (O157) and the ground beef background microflora (BM) was described in order to characterize the effects of enrichment factors on the growth of these organisms. The different enrichment factors studied were basal medium (Trypticase soy broth and E. coli broth), the presence of novobiocin in the broth, and the incubation temperature (37 degrees C or 40 degrees C). BM and O157 kinetics were simultaneously fitted by using a competitive growth model. The simple competition between the two microfloras implied that O157 growth stopped as soon as the maximal bacterial density in the BM was reached. The present study shows that the enrichment protocol factors had little impact on the simultaneous growth of BM and O157. The selective factors (i.e., bile salts and novobiocin) and the higher incubation temperature (40 degrees C) did not inhibit BM growth, and incubation at 40 degrees C only slightly improved O157 growth. The results also emphasize that when the level of O157 contamination in ground beef is low, the 6-h enrichment step recommended in the immunomagnetic separation protocol (ISO EN 16654) is not sufficient to detect O157 by screening methods. In this case, prior enrichment for approximately 10 h appears to be the optimal duration for enrichment. However, more experiments must be carried out with ground beef packaged in different ways in order to confirm the results obtained in the present study for non-vacuum- and non-modified-atmosphere-packed ground beef.
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Affiliation(s)
- A Vimont
- Unité de Microbiologie Alimentaire et Prévisionnelle, Ecole Nationale Vétérinaire de Lyon, 1 avenue Bourgelat, 69280 Marcy l'Etoile, France.
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Heyndrickx M, Rijpens N, Herman L. Molecular Detection and Typing of Foodborne Bacterial Pathogens: A Review. Appl Microbiol 2005. [DOI: 10.1007/0-306-46888-3_15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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9
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Prevalence of Shiga toxin-producing Escherichia coli in beef. Meat Sci 2005; 71:676-89. [DOI: 10.1016/j.meatsci.2005.05.012] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Revised: 05/12/2005] [Accepted: 05/12/2005] [Indexed: 01/28/2023]
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Bottero MT, Dalmasso A, Soglia D, Rosati S, Decastelli L, Civera T. Development of a multiplex PCR assay for the identification of pathogenic genes of Escherichia coli in milk and milk products. Mol Cell Probes 2004; 18:283-8. [PMID: 15271390 DOI: 10.1016/j.mcp.2004.03.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2004] [Accepted: 03/03/2004] [Indexed: 10/26/2022]
Abstract
A multiplex PCR for the simultaneous detection of some pathogenic genes of enteropathogenic, enterotoxigenic and verocytotoxin-producing Escherichia coli was developed. In this study primers found in literature as well as primers to the purpose designed were used. In this way, it was possible to generate specific fragments of 96, 170, 229, 285, 348, 414 and 510 bp for Hlya, St, EaeA, Lt, Vt1, UidA and Vt2 genes, respectively. When applied to bacterial strains experimentally inoculated in milk and milk products, the proposed PCR showed a detection limit of 5 x 10(4)CFU/ml for Hyla, St, Eaea, Vt1 primers, while for Lt and Vt2 primers the limit resulted of 10(6)CFU/ml.
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Affiliation(s)
- M T Bottero
- Dipartimento di Patologia Animale, Università degli Studi di Torino, Via Leonardo da Vinci 44, 10095 Grugliasco Torino, Italy.
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11
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Quantitative detection of Escherichia coli O157:H7 in ground beef by the polymerase chain reaction. Food Microbiol 2002. [DOI: 10.1006/fmic.2001.0477] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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12
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Bouvet J, Bavai C, Rossel R, Le Roux A, Montet MP, Ray-Gueniot S, Mazuy C, Arquillière C, Vernozy-Rozand C. Prevalence of verotoxin-producing Escherichia coli and E. coli O157:H7 in pig carcasses from three French slaughterhouses. Int J Food Microbiol 2001; 71:249-55. [PMID: 11789943 DOI: 10.1016/s0168-1605(01)00614-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Verotoxin-producing Escherichia coli (VTEC) are important food-borne pathogens in humans. Several studies have demonstrated that cattle are a major reservoir of VTEC but few data are available about the occurrence of VTEC in other species. In France, there is no data about pigs and pork meat. The main purpose of this study was to evaluate the prevalence of E. coli O157:H7 and other VTEC in pork carcasses. The second aim of the study was to get a picture of pork carcass contamination by VTEC. Pork carcasses from three French slaughterhouses (50 carcasses per slaughterhouse) were tested for the presence of VTEC and E. coli O157:H7. For each carcass, both internal and external sites were investigated (five on pig skin and three on muscles) and samples were collected by cutting out a surface of 25 cm2. A total of 1200 samples were analyzed by the polymerase chain reaction (PCR) after an enrichment step. Primers used were degenerate-sequences which allowed amplification of various types of verotoxin genes (stx). In addition, a second PCR which specifically detected E. coli O157:H7 was carried out on the stx-positive samples. The percentage of stx-positive PCR samples and carcasses was 12.7% (152/1200) and 50% (75/150), respectively. No E. coli O157:H7 was detected. The prevalence for each slaughterhouse was not significantly different. Skin samples of belly, leg and shoulder allowed detection of more than 80% of the VTEC positive carcasses.
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Affiliation(s)
- J Bouvet
- Unité de Microbiologie Alimentaire et Prévisionnelle, Ecole Nationale Vétérinaire de Lyon, Marcy l'Etoile, France.
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Ercolini D, Moschetti G, Blaiotta G, Coppola S. The potential of a polyphasic PCR-dGGE approach in evaluating microbial diversity of natural whey cultures for water-buffalo Mozzarella cheese production: bias of culture-dependent and culture-independent analyses. Syst Appl Microbiol 2001; 24:610-7. [PMID: 11876368 DOI: 10.1078/0723-2020-00076] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A polyphasic PCR-DGGE approach was used to describe the microbial population occurring in natural whey cultures (NWCs) for water-buffalo Mozzarella cheese production. Total microbial community was assessed without cultivation by analyzing DNA directly extracted from the original samples of NWC. In addition, DNA extracted from bulks of cells formed by harvesting colonies from the serial dilution agar plates of a variety of culture media was used to profile the "cultivable" community. The 16S rDNA V3 region was amplified using DNA from NWC as well as DNA from bulks as templates and the amplicons were separated by DGGE. The microbial entities occurring in NWCs were identified by partial 16S rDNA sequencing of DGGE bands: four lactic acid bacteria (LAB) closest relative of Streptococcus thermophilus, Lactococcus lactis, Lactobacillus delbrueckii and Lactobacillus crispatus were revealed by the analysis of DNA directly extracted from NWC while two other LAB, Lactobacillus fermentum and Enterococcus faecalis, were identified by analyzing DNA from the cultivable community. The developed PCR-DGGE analysis of the "cultivable" community showed good potential in evaluating microbial diversity of a dairy environment: it usefully highlighted the bias introduced by selective amplification when compared to the analysis of the total community from NWC and allowed suitability of media and growth conditions to be evaluated. Moreover, it could be used to complete the culture independent study of microbial diversity to give information on concentration ratios among species occurring in a particular environment and can be proposed for rapid identification of dominant microorganisms in alternative to traditional tools.
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Affiliation(s)
- D Ercolini
- Dipartimento di Scienza degli Alimenti, Alimentare e Ambientale e di Igiene, Stazione di Microbiologia Industriale, Università degli Studi di Napoli Federico II, Portici, Italy
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Fach P, Perelle S, Dilasser F, Grout J. Comparison between a PCR-ELISA test and the vero cell assay for detecting Shiga toxin-producing Escherichia coli in dairy products and characterization of virulence traits of the isolated strains. J Appl Microbiol 2001; 90:809-18. [PMID: 11348443 DOI: 10.1046/j.1365-2672.2001.01313.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIMS This paper provides information on a PCR-ELISA method for detecting Shiga toxin-producing Escherichia coli (STEC), and on their prevalence in dairy products. METHODS AND RESULTS The sensitivity and specificity of the test was evaluated using pure cultures, spiked and naturally-contaminated samples. A comparative study with vero cytotoxicity testing was conducted, and STEC isolated from naturally-contaminated samples were characterized. The PCR-ELISA test was highly specific and sensitive, and detected 14% more positive samples than the vero cell assay. The prevalence of STEC in raw milk and unpasteurized cheese was 21.5% and 30.5%, respectively, while samples from the 'dairy environment' and from pasteurized cheese were less contaminated. The 34 strains of STEC isolated from natural samples showed that some of them carried virulence genes. CONCLUSION No conclusion can be drawn at the moment concerning the potential risk to consumers. SIGNIFICANCE AND IMPACT OF THE STUDY These data show the necessity of valuable screening methods to appreciate the virulence of STEC.
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Affiliation(s)
- P Fach
- Agence Française de Sécurité Sanitaire des Aliments, Laboratoire d'Etudes et de Recherches sur l'Hygiène et la Qualité des Aliments, Unité: Atelier de Biotechnologie, Maisons-Alfort, France.
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Goodridge L, Chen J, Griffiths M. Development and characterization of a fluorescent-bacteriophage assay for detection of Escherichia coli O157:H7. Appl Environ Microbiol 1999; 65:1397-404. [PMID: 10103228 PMCID: PMC91198 DOI: 10.1128/aem.65.4.1397-1404.1999] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/1998] [Accepted: 11/09/1998] [Indexed: 11/20/2022] Open
Abstract
In this paper we describe evaluation and characterization of a novel assay that combines immunomagnetic separation and a fluorescently stained bacteriophage for detection of Escherichia coli O157:H7 in broth. When it was combined with flow cytometry, the fluorescent-bacteriophage assay (FBA) was capable of detecting 10(4) cells/ml. A modified direct epifluorescent-filter technique (DEFT) was employed in an attempt to estimate bacterial concentrations. Using regression analysis, we calculated that the lower detection limit was between 10(2) and 10(3) cells/ml; however, the modified DEFT was found to be an unreliable method for determining bacterial concentrations. The results of this study show that the FBA, when combined with flow cytometry, is a sensitive technique for presumptive detection of E. coli O157:H7 in broth cultures.
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Affiliation(s)
- L Goodridge
- Department of Food Science, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
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