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Fabre L, Le Hello S, Roux C, Issenhuth-Jeanjean S, Weill FX. CRISPR is an optimal target for the design of specific PCR assays for salmonella enterica serotypes Typhi and Paratyphi A. PLoS Negl Trop Dis 2014; 8:e2671. [PMID: 24498453 PMCID: PMC3907412 DOI: 10.1371/journal.pntd.0002671] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/13/2013] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Serotype-specific PCR assays targeting Salmonella enterica serotypes Typhi and Paratyphi A, the causal agents of typhoid and paratyphoid fevers, are required to accelerate formal diagnosis and to overcome the lack of typing sera and, in some situations, the need for culture. However, the sensitivity and specificity of such assays must be demonstrated on large collections of strains representative of the targeted serotypes and all other bacterial populations producing similar clinical symptoms. METHODOLOGY Using a new family of repeated DNA sequences, CRISPR (clustered regularly interspaced short palindromic repeats), as a serotype-specific target, we developed a conventional multiplex PCR assay for the detection and differentiation of serotypes Typhi and Paratyphi A from cultured isolates. We also developed EvaGreen-based real-time singleplex PCR assays with the same two sets of primers. PRINCIPAL FINDINGS We achieved 100% sensitivity and specificity for each protocol after validation of the assays on 188 serotype Typhi and 74 serotype Paratyphi A strains from diverse genetic groups, geographic origins and time periods and on 70 strains of bacteria frequently encountered in bloodstream infections, including 29 other Salmonella serotypes and 42 strains from 38 other bacterial species. CONCLUSIONS The performance and convenience of our serotype-specific PCR assays should facilitate the rapid and accurate identification of these two major serotypes in a large range of clinical and public health laboratories with access to PCR technology. These assays were developed for use with DNA from cultured isolates, but with modifications to the assay, the CRISPR targets could be used in the development of assays for use with clinical and other samples.
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Affiliation(s)
- Laetitia Fabre
- Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, WHO Collaborative Center for Reference and Research on Salmonella, Institut Pasteur, Paris, France
| | - Simon Le Hello
- Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, WHO Collaborative Center for Reference and Research on Salmonella, Institut Pasteur, Paris, France
| | - Chrystelle Roux
- Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, WHO Collaborative Center for Reference and Research on Salmonella, Institut Pasteur, Paris, France
| | - Sylvie Issenhuth-Jeanjean
- Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, WHO Collaborative Center for Reference and Research on Salmonella, Institut Pasteur, Paris, France
| | - François-Xavier Weill
- Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, WHO Collaborative Center for Reference and Research on Salmonella, Institut Pasteur, Paris, France
- * E-mail:
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52
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Hemolytic uremic syndrome following infection with O111 Shiga toxin-producing Escherichia coli revealed through molecular diagnostics. J Clin Microbiol 2013; 52:1003-5. [PMID: 24371241 DOI: 10.1128/jcm.02855-13] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We report a case of hemolytic uremic syndrome in a 69-year-old woman due to Shiga toxin-producing Escherichia coli, possibly serotype O111, to illustrate the potentially deleterious implications of a Campylobacter enzyme immunoassay (EIA) result and the increasing importance of molecular testing when conventional methods are limited.
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53
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Miko A, Delannoy S, Fach P, Strockbine NA, Lindstedt BA, Mariani-Kurkdjian P, Reetz J, Beutin L. Genotypes and virulence characteristics of Shiga toxin-producing Escherichia coli O104 strains from different origins and sources. Int J Med Microbiol 2013; 303:410-21. [DOI: 10.1016/j.ijmm.2013.05.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 05/07/2013] [Accepted: 05/20/2013] [Indexed: 02/03/2023] Open
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Shariat N, Sandt CH, DiMarzio MJ, Barrangou R, Dudley EG. CRISPR-MVLST subtyping of Salmonella enterica subsp. enterica serovars Typhimurium and Heidelberg and application in identifying outbreak isolates. BMC Microbiol 2013; 13:254. [PMID: 24219629 PMCID: PMC3840669 DOI: 10.1186/1471-2180-13-254] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Accepted: 11/04/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Salmonella enterica subsp. enterica serovars Typhimurium (S. Typhimurium) and Heidelberg (S. Heidelberg) are major causes of foodborne salmonellosis, accounting for a fifth of all annual salmonellosis cases in the United States. Rapid, efficient and accurate methods for identification are required for routine surveillance and to track specific strains during outbreaks. We used Pulsed-field Gel Electrophoresis (PFGE) and a recently developed molecular subtyping approach termed CRISPR-MVLST that exploits the hypervariable nature of virulence genes and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) to subtype clinical S. Typhimurium and S. Heidelberg isolates. RESULTS We analyzed a broad set of 175 S. Heidelberg and S. Typhimurium isolates collected over a five-year period. We identified 21 Heidelberg Sequence Types (HSTs) and 37 Typhimurium STs (TSTs) that were represented by 27 and 45 PFGE pulsotypes, respectively, and determined the discriminatory power of each method. CONCLUSIONS For S. Heidelberg, our data shows that combined typing by both CRISPR-MVLST and PFGE provided a discriminatory power of 0.9213. Importantly, CRISPR-MVLST was able to separate common PFGE patterns such as JF6X01.0022 into distinct STs, thus providing significantly greater discriminatory power. Conversely, we show that subtyping by either CRISPR-MVLST or PFGE independently provides a sufficient discriminatory power (0.9345 and 0.9456, respectively) for S. Typhimurium. Additionally, using isolates from two S. Typhimurium outbreaks, we demonstrate that CRISPR-MVLST provides excellent epidemiologic concordance.
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Affiliation(s)
- Nikki Shariat
- Department of Food Science, The Pennsylvania State University, University Park, PA 16802, USA
| | - Carol H Sandt
- The Pennsylvania Department of Health, Bureau of Laboratories, Division of Clinical Microbiology, Exton, PA 19341, USA
| | - Michael J DiMarzio
- Department of Food Science, The Pennsylvania State University, University Park, PA 16802, USA
| | - Rodolphe Barrangou
- Department of Food Science, The Pennsylvania State University, University Park, PA 16802, USA
- Current address: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695, USA
| | - Edward G Dudley
- Department of Food Science, The Pennsylvania State University, University Park, PA 16802, USA
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55
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Abstract
Rapid and accurate strain identification is paramount in the battle against microbial outbreaks, and several subtyping approaches have been developed. One such method uses clustered regular interspaced short palindromic repeats (CRISPRs), DNA repeat elements that are present in approximately half of all bacteria. Though their signature function is as an adaptive immune system against invading DNA such as bacteriophages and plasmids, CRISPRs also provide an excellent framework for pathogen tracking and evolutionary studies. Analysis of the spacer DNA sequences that reside between the repeats has been tremendously useful for bacterial subtyping during molecular epidemiological investigations. Subtyping, or strain identification, using CRISPRs has been employed in diverse Gram-positive and Gram-negative bacteria, including Mycobacterium tuberculosis, Salmonella enterica, and the plant pathogen Erwinia amylovora. This review discusses the several ways in which CRISPR sequences are exploited for subtyping. This includes the well-established spoligotyping methodologies that have been used for 2 decades to type Mycobacterium species, as well as in-depth consideration of newer, higher-throughput CRISPR-based protocols.
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56
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Yin S, Jensen MA, Bai J, DebRoy C, Barrangou R, Dudley EG. The evolutionary divergence of Shiga toxin-producing Escherichia coli is reflected in clustered regularly interspaced short palindromic repeat (CRISPR) spacer composition. Appl Environ Microbiol 2013; 79:5710-20. [PMID: 23851088 PMCID: PMC3754162 DOI: 10.1128/aem.00950-13] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2013] [Accepted: 07/08/2013] [Indexed: 11/20/2022] Open
Abstract
The Shiga toxin-producing Escherichia coli (STEC) strains, including those of O157:H7 and the "big six" serogroups (i.e., serogroups O26, O45, O103, O111, O121, and O145), are a group of pathogens designated food adulterants in the United States. The relatively conserved nature of clustered regularly interspaced short palindromic repeats (CRISPRs) in phylogenetically related E. coli strains makes them potential subtyping markers for STEC detection, and a quantitative PCR (qPCR)-based assay was previously developed for O26:H11, O45:H2, O103:H2, O111:H8, O121:H19, O145:H28, and O157:H7 isolates. To better evaluate the sensitivity and specificity of this qPCR method, the CRISPR loci of 252 O157 and big-six STEC isolates were sequenced and analyzed along with 563 CRISPR1 and 624 CRISPR2 sequences available in GenBank. General conservation of spacer content and order was observed within each O157 and big-six serogroup, validating the qPCR method. Meanwhile, it was found that spacer deletion, the presence of an insertion sequence, and distinct alleles within a serogroup are sources of false-negative reactions. Conservation of CRISPR arrays among isolates expressing the same flagellar antigen, specifically, H7, H2, and H11, suggested that these isolates share an ancestor and provided an explanation for the false positives previously observed in the qPCR results. An analysis of spacer distribution across E. coli strains provided limited evidence for temporal spacer acquisition. Conversely, comparison of CRISPR sequences between strains along the stepwise evolution of O157:H7 from its O55:H7 ancestor revealed that, over this ∼7,000-year span, spacer deletion was the primary force generating CRISPR diversity.
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Affiliation(s)
- Shuang Yin
- Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania, USA
| | | | - Jiawei Bai
- Department of Biostatistics, Johns Hopkins University, Baltimore, Maryland, USA
| | - Chitrita DebRoy
- E. coli Reference Center, Department of Veterinary and Biomedical Sciences, The Pennsylvania State University, University Park, Pennsylvania, USA
| | - Rodolphe Barrangou
- Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA
| | - Edward G. Dudley
- Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania, USA
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Douillard FP, Ribbera A, Kant R, Pietilä TE, Järvinen HM, Messing M, Randazzo CL, Paulin L, Laine P, Ritari J, Caggia C, Lähteinen T, Brouns SJJ, Satokari R, von Ossowski I, Reunanen J, Palva A, de Vos WM. Comparative genomic and functional analysis of 100 Lactobacillus rhamnosus strains and their comparison with strain GG. PLoS Genet 2013; 9:e1003683. [PMID: 23966868 PMCID: PMC3744422 DOI: 10.1371/journal.pgen.1003683] [Citation(s) in RCA: 152] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 06/15/2013] [Indexed: 01/20/2023] Open
Abstract
Lactobacillus rhamnosus is a lactic acid bacterium that is found in a large variety of ecological habitats, including artisanal and industrial dairy products, the oral cavity, intestinal tract or vagina. To gain insights into the genetic complexity and ecological versatility of the species L. rhamnosus, we examined the genomes and phenotypes of 100 L. rhamnosus strains isolated from diverse sources. The genomes of 100 L. rhamnosus strains were mapped onto the L. rhamnosus GG reference genome. These strains were phenotypically characterized for a wide range of metabolic, antagonistic, signalling and functional properties. Phylogenomic analysis showed multiple groupings of the species that could partly be associated with their ecological niches. We identified 17 highly variable regions that encode functions related to lifestyle, i.e. carbohydrate transport and metabolism, production of mucus-binding pili, bile salt resistance, prophages and CRISPR adaptive immunity. Integration of the phenotypic and genomic data revealed that some L. rhamnosus strains possibly resided in multiple niches, illustrating the dynamics of bacterial habitats. The present study showed two distinctive geno-phenotypes in the L. rhamnosus species. The geno-phenotype A suggests an adaptation to stable nutrient-rich niches, i.e. milk-derivative products, reflected by the alteration or loss of biological functions associated with antimicrobial activity spectrum, stress resistance, adaptability and fitness to a distinctive range of habitats. In contrast, the geno-phenotype B displays adequate traits to a variable environment, such as the intestinal tract, in terms of nutrient resources, bacterial population density and host effects. Some bacterial species are specialists and adapted to a single niche, while others are generalists and able to grow in various environmental conditions. Lactobacillus rhamnosus is a generalist and its members can often be found in different human cavities but also in various artisanal and industrial dairy products. To gain insights into the genetic complexity and ecological versatility of this species, we collected 100 L. rhamnosus strains from different niches. Genomic and functional analysis of these revealed a dichotomy within the species that reflected its adaptation to particular niches. The variable regions identified in the L. rhamnosus genome encode lifestyle traits that allowed us to demonstrate that some L. rhamnosus isolates possibly resided in multiple habitats. Our work brings valuable data on the ecological dynamics and adaptability of the species and provides a basis for a model explaining the ecology of L. rhamnosus in an anthropocentric perspective. Finally, we observed that a set of pheno-genomic markers, i.e. CRISPR oligotyping or carbohydrate metabolism, would be sufficient and among the best ways to differentiate the L. rhamnosus strains, providing a general approach to select the highest diversity in these and other bacterial species.
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Affiliation(s)
- François P Douillard
- Department of Veterinary Biosciences, University of Helsinki, Helsinki, Finland.
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Discrimination of enterohemorrhagic Escherichia coli (EHEC) from non-EHEC strains based on detection of various combinations of type III effector genes. J Clin Microbiol 2013; 51:3257-62. [PMID: 23884997 DOI: 10.1128/jcm.01471-13] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Enterohemorrhagic Escherichia coli (EHEC) strains comprise a subgroup of Shiga-toxin (Stx)-producing E. coli (STEC) and are characterized by a few serotypes. Among these, seven priority STEC serotypes (O26:H11, O45:H2, O103:H2, O111:H8, O121:H19, O145:H28, and O157:H7) are most frequently implicated in severe clinical illness worldwide. Currently, standard methods using stx, eae, and O-serogroup-specific gene sequences for detecting the top 7 EHEC serotypes bear the disadvantage that these genes can be found in non-EHEC strains as well. Here, we explored the suitability of ureD, espV, espK, espN, Z2098, and espM1 genes and combinations thereof as candidates for a more targeted EHEC screening assay. For a very large panel of E. coli strains (n = 1,100), which comprised EHEC (n = 340), enteropathogenic E. coli (EPEC) (n = 392), STEC (n = 193), and apathogenic strains (n = 175), we showed that these genetic markers were more prevalent in EHEC (67.1% to 92.4%) than in EPEC (13.3% to 45.2%), STEC (0.5% to 3.6%), and apathogenic E. coli strains (0 to 2.9%). It is noteworthy that 38.5% of the EPEC strains that tested positive for at least one of these genetic markers belonged to the top 7 EHEC serotypes, suggesting that such isolates might be Stx-negative derivatives of EHEC. The associations of espK with either espV, ureD, or Z2098 were the best combinations for more specific and sensitive detection of the top 7 EHEC strains, allowing detection of 99.3% to 100% of these strains. In addition, detection of 93.7% of the EHEC strains belonging to other serotypes than the top 7 offers a possibility for identifying new emerging EHEC strains.
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Katyal I, Chaban B, Ng B, Hill JE. CRISPRs of Enterococcus faecalis and E. hirae isolates from pig feces have species-specific repeats but share some common spacer sequences. MICROBIAL ECOLOGY 2013; 66:182-188. [PMID: 23535981 DOI: 10.1007/s00248-013-0217-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2012] [Accepted: 03/11/2013] [Indexed: 06/02/2023]
Abstract
Clustered regularly interspaced short palindromic repeats (CRISPR) are currently a topic of interest in microbiology due to their role as a prokaryotic immune system. Investigations of CRISPR distribution and characterization to date have focused on pathogenic bacteria, while less is known about CRISPR in commensal bacteria, where they may have a significant role in the ecology of the microbiota of humans and other animals, and act as a recorder of interactions between bacteria and viruses. A combination of PCR and sequencing was used to determine prevalence and distribution of CRISPR arrays in Enterococcus faecalis and Enterococcus hirae isolates from the feces of healthy pigs. Both type II CRISPR-Cas and Orphan CRISPR (without Cas genes) were detected in the 195 isolates examined. CRISPR-Cas was detected in 52 (46/88) and 42 % (45/107) E. faecalis and E. hirae isolates, respectively. The prevalence of Orphan CRISPR arrays was higher in E. faecalis isolates (95 %, 84/88) compared with E. hirae isolates (49 %, 53/107). Species-specific repeat sequences were identified in Orphan CRISPR arrays, and 42 unique spacer sequences were identified. Only two spacers matched previously characterized pig virome sequences, and many were apparently derived from chromosomal sequences of enterococci. Surprisingly, 17 (40 %) of the spacers were detected in both species. Shared spacer sequences are evidence of a lack of species specificity in the agents and mechanisms responsible for integration of spacers, and the abundance of spacer sequences corresponding to bacterial chromosomal sequences reflects interspecific interactions within the intestinal microbiota.
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Affiliation(s)
- Isha Katyal
- Department of Veterinary Microbiology, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK, S7N 5B4, Canada
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60
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Shariat N, Kirchner MK, Sandt CH, Trees E, Barrangou R, Dudley EG. Subtyping of Salmonella enterica serovar Newport outbreak isolates by CRISPR-MVLST and determination of the relationship between CRISPR-MVLST and PFGE results. J Clin Microbiol 2013; 51:2328-36. [PMID: 23678062 PMCID: PMC3697709 DOI: 10.1128/jcm.00608-13] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Accepted: 05/05/2013] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica subsp. enterica serovar Newport (S. Newport) is the third most prevalent cause of food-borne salmonellosis. Rapid, efficient, and accurate methods for identification are required to track specific strains of S. Newport during outbreaks. By exploiting the hypervariable nature of virulence genes and clustered regularly interspaced short palindromic repeats (CRISPRs), we previously developed a sequence-based subtyping approach, designated CRISPR-multi-virulence-locus sequence typing (CRISPR-MVLST). To demonstrate the applicability of this approach, we analyzed a broad set of S. Newport isolates collected over a 5-year period by using CRISPR-MVLST and pulsed-field gel electrophoresis (PFGE). Among 84 isolates, we defined 38 S. Newport sequence types (NSTs), all of which were novel compared to our previous analyses, and 62 different PFGE patterns. Our data suggest that both subtyping approaches have high discriminatory abilities (>0.95) with a potential for clustering cases with common exposures. Importantly, we found that isolates from closely related NSTs were often similar by PFGE profile as well, further corroborating the applicability of CRISPR-MVLST. In the first full application of CRISPR-MVLST, we analyzed isolates from a recent S. Newport outbreak. In this blinded study, we confirmed the utility of CRISPR-MVLST and were able to distinguish the 10 outbreak isolates, as defined by PFGE and epidemiological data, from a collection of 20 S. Newport isolates. Together, our data show that CRISPR-MVLST could be a complementary approach to PFGE subtyping for S. Newport.
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Affiliation(s)
- Nikki Shariat
- Department of Food Science, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Margaret K. Kirchner
- Department of Food Science, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Carol H. Sandt
- Bureau of Laboratories, Division of Clinical Microbiology, Pennsylvania Department of Health, Exton, Pennsylvania, USA
| | - Eija Trees
- Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Rodolphe Barrangou
- Department of Food Science, Pennsylvania State University, University Park, Pennsylvania, USA
- Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA
| | - Edward G. Dudley
- Department of Food Science, Pennsylvania State University, University Park, Pennsylvania, USA
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Wang F, Yang Q, Kase JA, Meng J, Clotilde LM, Lin A, Ge B. Current trends in detecting non-O157 Shiga toxin-producing Escherichia coli in food. Foodborne Pathog Dis 2013; 10:665-77. [PMID: 23755895 DOI: 10.1089/fpd.2012.1448] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Non-O157 Shiga toxin-producing Escherichia coli (non-O157 STEC) strains are increasingly recognized as important foodborne pathogens worldwide. Together with E. coli O157:H7, six additional STEC serogroups (O26, O45, O103, O111, O121, and O145) are now regulated as adulterants in certain raw beef products in the United States. However, effective detection and isolation of non-O157 STEC strains from food matrices remain challenging. In the past decade, great attention has been paid to developing rapid and reliable detection methods for STEC in general (targeting common virulence factors) and specific STEC serogroups in particular (targeting serogroup-specific traits). This review summarizes current trends in detecting non-O157 STEC in food, including culture, immunological, and molecular methods, as well as several novel technologies.
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Affiliation(s)
- Fei Wang
- Department of Food Science, Louisiana State University Agricultural Center , Baton Rouge, Louisiana, USA
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62
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Towards a molecular definition of enterohemorrhagic Escherichia coli (EHEC): detection of genes located on O island 57 as markers to distinguish EHEC from closely related enteropathogenic E. coli strains. J Clin Microbiol 2013; 51:1083-8. [PMID: 23325824 DOI: 10.1128/jcm.02864-12] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Among strains of Shiga-toxin (Stx) producing Escherichia coli (STEC), seven serogroups (O26, O45, O103, O111, O121, O145, and O157) are associated with severe clinical illness in humans. These strains are also called enterohemorrhagic E. coli (EHEC), and the development of methods for their reliable detection from food has been challenging thus far. PCR detection of major EHEC virulence genes stx1, stx2, eae, and O-serogroup-specific genes is useful but does not identify EHEC strains specifically. Searching for the presence of additional genes issued from E. coli O157:H7 genomic islands OI-122 and OI-71 increases the specificity but does not clearly discriminate EHEC from enteropathogenic E. coli (EPEC) strains. Here, we identified two putative genes, called Z2098 and Z2099, from the genomic island OI-57 that were closely associated with EHEC and their stx-negative derivative strains (87% for Z2098 and 91% for Z2099). Z2098 and Z2099 were rarely found in EPEC (10% for Z2098 and 12% for Z2099), STEC (2 and 15%), and apathogenic E. coli (1% each) strains. Our findings indicate that Z2098 and Z2099 are useful genetic markers for a more targeted diagnosis of typical EHEC and new emerging EHEC strains.
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