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Single-Strand Conformation Polymorphisms in the hly Gene and Polymerase Chain Reaction Analysis of a Repeat Region in the iap Gene to Identify and Type Listeria monocytogenes

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Two novel methods that allow the powerful identification of Listeria monocytogenes by polymerase chain reaction (PCR) and simultaneous differentiation by special electrophoresis formats are described. The first method involves a PCR-driven single-strand conformation polymorphism (SSCP-PCR) assay using a portion of the noncoding region of the hly gene. The assay was evaluated with 120 genetically distinct L. monocytogenes strains of either foodborne or clinical origin. Distribution of listerial strains to at least 14 SSCP types was observed. In respect to the panel of strains, 39.7% were assigned to SSCP type 3, and 19% showed SSCP type 5. Further, SSCP type 1 was found in 7.5% of all strains, SSCP type 10 in 6.7%, and 5.8% each for SSCP types 6 and 7. The SSCP types 4, 9, and 11 were infrequently described in 2.55%, 3.3%, and 4.2%, respectively, of all isolates. At least 0.85% represented each of the SSCP types 2, 13, and 14, and 1.7% displayed SSCP types 8 and 12. In the second method, the internal threonine-asparagine repeat portion of the L. monocytogenes p60 protein was used for setting up a PCR-based identification and parallel differentiation assay. Ten different repeat types (RTs), according to different sizes of PCR products, were observed. Of 163 strains tested, 35.58% of samples were assigned to RT 1, 39.26% to RT 2, 3.68% to RT 3, 6.13% to RT 4, 4.29% to RT 5, 2.45% to RT 6, 5.52% to RT 7, 0.61% to RT 8, 0.61% to RT 9, and 1.83% to RT 10. The data suggest that both methods allow the simple identification and differentiation of L. monocytogenes isolates. Therefore, both the SSCP-PCR and the PCR-based identification and parallel differentiation assay could represent single-strand pretyping assays before laborious reference typing methods are applied.

Document Type: Research Article

Affiliations: 1: Institute for Milk Hygiene, Milk Technology, and Food Science, University of Veterinary Medicine, Veterinärplatz 1, Vienna, Austria 2: Institute for Virology, University of Veterinary Medicine, Veterinärplatz 1, Vienna, Austria 3: Theodor-Boveri-Institute for Biosciences, Department for Microbiology, Am Hubland, 97074 Würzburg, Germany; Microbiological Analytics, Merck KgaA, Frankfurter Strasse 250, 64293 Darmstadt, Germany

Publication date: March 1, 2000

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