University of Helsinki

Research groups: Food and environmental hygiene

Molecular epidemiology and genomics of psychrotrophic and spore-forming food-borne pathogens

Director of research: Professor Hannu Korkeala

Abstract. The main focus has been molecu­lar biolo­gi­cal detec­ti­on met­hods, taxonomy, virulence mechanisms and epide­miologi­cal aspects of spore-forming and/or psychrotrophic Clostridium botulinum, Clostridium perfringens, Liste­ria monocy­togenes, Yersinia entero­colitica and Yersinia pseudotuberculosis. The reservoirs of these pathogens have been determined. Food items associated with food hygienic risks of C. botulinum, L. monocy­togenes, Y. entero­colitica and Y. pseudotuberculosis have been identified. Molecular epidemiology is used for the identification and investigation of food poisoning outbreaks. In order to improve the prevention of food poisoning outbreaks, we have studied the sources and contamination routes of these food-bor­ne pathogenic bacteria in primary production, in the food industry, and at the retail market. Genetic diversity of these pathogens has been studied. For these purposes we have applied ribo­typing, pulsed-field gel electropho­resis (PFGE), amplified fragment length polymorphism (AFLP) and DNA microarrays. Research on the functional genomics of C. botulinum has been started using the microarray technique. Food processing methods have been improved in order to guarantee product safety.

Researchers: Professor Hannu Korkeala, DVM, PhD Maria Fredriksson-Ahomaa, DVM, PhD Miia Lindström, DVM, PhD Janne Lundén, Aivars Berzins, Annamari Heikinheimo, Sanna Hellström, Susanna Kangas, Riikka Keto-Timonen, Katri Kiviniemi, Päivi Lahti, Annukka Markkula, Lauri Merivirta, Maria Miettinen, Mari Nevas, Taina Niskanen, Pilar Ortiz, Kristi Praakle, Riikka Laukkanen, Riina Tolvanen.

Use of amplified fragment length polymorphism (AFLP) method in molecular typing of foodborne pathogens

Amplified fragment length polymorphism (AFLP) analysis is a DNA-based typing method that has been shown to be fast, highly reproducible and discriminative. The aim of the study is to assess the applicability of AFLP analysis in investigation of the biodiversity and epidemiology of pathogens. In addition, the usefulness of AFLP in differentiation and identification of bacteria at the species level is studied. Special attention is paid on L. monocytogenes, C. botulinum and other clostridia. A DNA fingerprint database is being created. The database is used in other research projects and in possible contamination route and outbreak studies. The project is led by Professor Hannu Korkeala and the corresponding researcher is Riikka Keto-Timonen, DVM.

Genetic diversity and functional genomics of Clostridium botulinum

The project focuses on the genetic diversity of C. botulinum using DNA microarrays. Furthermore, the mechanisms behind botulinum toxin formation and the cold response of C. botulinum are researched by genome-wide expression analysis using the microarray. The project is done in collaboration with the Institute of Food Research, Norwich, UK and the University of Nottingham, UK, the Institute of Biotechnology and the Department of Plant Pathology at the University of Helsinki, and the National Veterinary and Food Research Institute. The project is funded by the Academy of Finland, the Ministry of Agriculture and Forestry, TEKES and Walter Ehrström Foundation. The project is led by Professor Hannu Korkeala and the corresponding researchers are Miia Lindström, DVM, PhD and Katri Kiviniemi, DVM.

The role of small mammals in epidemiology of Yersinia pseudotuberculosis

The bacterium Y. pseudotuberculosis is common in soil, water and wild animals. In recent years, the sources of Y. pseudotuberculosis outbreaks have been vegetables, and in the 2004 outbreak the same Y. pseudotuberculosis genotypes were isolated from humans, carrots and small mammals caught from the farm cultivating the carrots that were associated with the outbreak. The project is done in collaboration with prof. Heikki Henttonen (Finnish Forest Research Institute, Metla) and it is led by Professor Hannu Korkeala and the corresponding researcher is Susanna Kangas, DVM.

Multilocus Sequence Typing of Yersinia pseudotuberculosis strains

Multilocus sequence typing (MLST) is a novel nucleotide sequence based method for bacterial typing. In this project we establish MLST to type Yersinia pseudotuberculosis strains from all continents (excluding Antarctic) and elucidate its global epidemiology and evolution. The project leader is Professor Mikael Skurnik (Haartman Institute, University of Helsinki, Finland) and the corresponding researcher is Riikka Laukkanen, DVM. Professor Hannu Korkeala and Riikka Laukkanen from the Department of Food and Environmental Hygiene participate in the project. T he research is done in collaboration with Dr Mark Achtman (Max-Planck Institute, Germany), Professor Martin Maiden ( University of Oxford, England), Dr Hiroshi Fukushima (Shimane Prefectural Institute of Public Health and Environmental Science, Japan), Dr Elisabeth Carniel (Pasteur Institute, France), Dr Galina Tseneva (Pasteur Institute, Russia) and Dr Anja Siitonen (National Public Health Institute, Finland).

Psychrotrophic lactic acid bacteria associated with microbial diversity of foods: taxonomy, metabolism in food spoilage and food processing hygiene

Director of research: Björkroth, Katri Johanna; professori; Department of Food and Environmental Hygiene; johanna.bjorkroth@helsinki.fi

Abstract: We have focused our research on the lactic acid bacteria (LAB) causing spoilage in foods. We study how these LAB contaminate foods and what can be done to prevent this in order to maintain good food quality through shelf life. The systematics of food-associated LAB species and their metabolism are also important research topics. Different DNA-based techniques have been applied to these studies. Restriction endonuclease and rRNA gene RFLP analyses (ribotypes) have shown to be excellent as taxonomy tools and in tracing down bacterial contamination at various food processing premises. We have been using these techniques for the detection of critical points associated with lactic acid bacterium contamination. Specific spoilage organisms (SSO) have been characterized further using pulsed-field gel electrophoresis, AFLP or other suitable techniques in order to evaluate clonal variation of strains. These techniques together with sequence-based and phenotypic approaches are used also for polyp hasic taxonomic analyses and studies related to the development of specific spoilage microbiota in different foods. Studies are currently dealing with Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Streptococcus and Weissella species. LAB spoilage related to different meat and fish products is mainly dealt with but occasionally wider works dealing with LAB biodiversity as general have been carried out. Lately, we have also stared a project dealing with the metabolic properties of a spoilage LAB (Leuconostoc gasicomitatum) together with the Institute of Biotechnology. The general aim of our work is to provide basic information of different spoilage and contamination events in order to improve quality of various food products.

Researchers: Björkroth, Johanna ; Koort, Joanna ; Lundström, Hanna-Saara ; Merivirta, Lauri ; Murros, Anna ; Vihavainen, Elina ; Ulvila, Juha

Molecular toxicity mechanisms of dioxins

Dioxins are globally ubiquitous environmental contaminants that elicit a host of biochemical and toxic effects at very low dose levels in laboratory animals. They tend to accumulate in the food chain and their elimination half-lives in humans are notably long (many years). Therefore, their possible health hazards have given reason for concern. Risk assessment of dioxins is hampered by the fact that their mechanisms of toxicity are poorly known. In addition, there exist exceptionally wide inter- and even intra-species differences in sensitivity to some adverse effects of dioxins, especially acute lethality.

The objective of this research project is to shed more light on the following four questions essential to the acute toxicity of dioxins: (1) How does sensitivity to dioxins (and to their tissue impacts) depend on the structure of the AH receptor (which mediates most of the biological effects of dioxins) with particular reference to its carboxyterminal end? (2) Which other proteins does the AHR interact with and what is the significance of these protein-protein interactions for dioxin toxicity? (3) To which extent are the acute toxicity of dioxins and its most characteristic external sign in laboratory animals, the wasting syndrome, due to toxicity of the central nervous system vs. deranged peripheral energy metabolism (especially in liver)? (4) Induction/repression of which genes in key target tissues is causally related with the acute lethality of dioxins?

To solve these questions, we have exceptionally efficient animal models at our disposal including two rat strains (discovered by us some 20 years ago) with an over 1000-fold sensitivity difference to the acute lethality of the most potent dioxin, TCDD, and novel transgenic mouse models one of which stems from the rat model. The research rests on modern molecular biological methods such as genome-wide transcriptomic analyses with DNA microarrays and measurement of expression levels of individual genes by quantitative real-time RT-PCR. The most important collaborators are: Informatics and Biocomputing Platform, Ontario Institute for Cancer Research, Toronto, Canada (Dr. Paul Boutros); Laboratory of Toxicology, National Institute for Health and Welfare, Kuopio (Doc. Matti Viluksela); and Department of Pharmaceutics, University of Kuopio, Kuopio (Prof. Paavo Honkakoski).

Apart from their substantial toxicological significance, the results obtained may also further understanding of physiological and pathological regulation of body weight and food intake, because TCDD is the most potent weight-reducing compound known: a single dose may halt the growth of rats doggedly or even perpetually.

Over the period of 2002-2007, the project participated in the national Center of Excellence in Environmental Health Risk Analysis coordinated by the National Public Health Institute.

Leader of the research project: Professor Raimo Pohjanvirta, tel. +358 9 191 57147, e-mail raimo.pohjanvirta@helsinki.fi. Researchers: Jere Lindén (D.V.M.). Another researcher is to be engaged in 2010. Technical assistance: Ms. Susanna Lukkarinen.