title: Development of a real-time PCR method coupled with a selective pre-enrichment step for quantification of Morganella morganii and Morganella psychrotolerans in fish products.
abstract: Histamine fish poisoning is common and due to toxic concentrations of histamine often produced by Gram-negative bacteria in fin-fish products with a high content of the free amino acid histidine. The genus Morganella includes two species previously reported to cause incidents of histamine fish poisoning. Morganella morganii and Morganella psychrotolerans are both strong producer of histamine. However, little is known about the occurrence and critical stages for fish contamination with these bacteria. To elucidate contamination routes of Morganella, specific real-time quantitative PCR (RTi qPCR) methods for quantification of M. morganii and M. psychrotolerans have been developed. Selective primers amplified a 110 bp region of the vasD gene for M. psychrotolerans and a 171 bp region of the galactokinase gene for M. morganii. These primer-sets showed high specificity as demonstrated by using purified DNA from 23 other histamine producing bacteria and 26 isolates with no or limited histamine production. The efficiency of the qPCR reactions on artificially contaminated fish samples were 100.8% and 96.3% respectively. The limit of quantification (LOQ) without enrichment was 4 log CFU/g. A quantitative enrichment step with a selective medium was included and improved the sensitivity of the methods to a LOQ of below 50 CFU/g in seafood. RTi qPCR methods with or without enrichment were evaluated for enumeration of Morganella species in naturally contaminated fresh fish and lightly preserved seafood from Denmark. These new methods will contribute to a better understanding of the occurrence and histamine production by Morganella species in fish products, information that is essential to reduce the unacceptably high frequency of histamine fish poisoning.
authors: Ifremer, Laboratory of Microbial Ecosystem and Marine Molecules for Biotechnology, Nantes, France; LUNAM Université, Oniris, UMR1014, Secalim, Nantes, France; INRA, Nantes, France.
authors: Gaëtan
authors: G
authors: Podeur
authors: National Food Institute (DTU Food), Technical University of Denmark, Kgs. Lyngby, Denmark.
authors: Paw
authors: P
authors: Dalgaard
authors: Ifremer, Laboratory of Microbial Ecosystem and Marine Molecules for Biotechnology, Nantes, France.
authors: Francoise
authors: F
authors: Leroi
authors: LUNAM Université, Oniris, UMR1014, Secalim, Nantes, France; INRA, Nantes, France.
authors: Hervé
authors: H
authors: Prévost
authors: National Food Institute (DTU Food), Technical University of Denmark, Kgs. Lyngby, Denmark.
authors: Jette
authors: J
authors: Emborg
authors: DTU System Biology, Technical University of Denmark, Kgs. Lyngby, Denmark.
authors: Jan
authors: J
authors: Martinussen
authors: Department of Environmental Science, Aarhus University, Roskilde, Denmark.
authors: Lars Hestbjerg
authors: LH
authors: Hansen
authors: LUNAM Université, Oniris, UMR1014, Secalim, Nantes, France; INRA, Nantes, France. Electronic address: marie-france.pilet@oniris-nantes.fr.
authors: Marie-France
authors: MF
authors: Pilet
mesh_terms: D000818:Animals; D046508:Culture Techniques; D017931:DNA Primers / Q000235:genetics; D003718:Denmark; D005396:Fish Products / Q000382:microbiology*; D005399:Fishes / Q000382:microbiology; D005516:Food Microbiology / Q000379:methods*; D005517:Foodborne Diseases / Q000517:prevention & control; D006632:Histamine / Q000378:metabolism; D020596:Morganella / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D020613:Morganella morganii / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D060888:Real-Time Polymerase Chain Reaction; D017747:Seafood / Q000382:microbiology; D012680:Sensitivity and Specificity
chemical_list: D017931:DNA Primers; D006632:Histamine
keywords: Enterobacteriaceae; Galactokinase; Histamine-producing bacteria; Selective medium; Tuna; Type VI secretion system