Hannu Korkeala

Publications (121)331.24 Total impact

• Article: Plasmid-borne type E neurotoxin gene clusters in Clostridium botulinum strains.

  Zhen Zhang, Hannamari Hintsa, Ying Chen, Hannu Korkeala, Miia Lindström
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  ABSTRACT: A collection of 36 Clostridium botulinum type E strains was examined by pulsed-field gel electrophoresis (PFGE) and Southern hybridization with probes targeted to botE and orfX1 in the neurotoxin gene cluster. Three strains were found to encode neurotoxin subtype E1 gene clusters in large plasmids of about 146 kb in size.
  Applied and environmental microbiology 04/2013; · 3.69 Impact Factor
• Article: Alternative sigma factor SigK has a role in stress tolerance of group I Clostridium botulinum ATCC 3502.

  Elias Dahlsten, David Kirk, Miia Lindström, Hannu Korkeala
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  ABSTRACT: The role of the alternative sigma factor SigK in cold and osmotic stress tolerance of Clostridium botulinum ATCC 3502 was demonstrated by induction of sigK after temperature downshift and exposure to hyperosmotic conditions, and by impaired growth of the sigK mutants under respective conditions.
  Applied and environmental microbiology 04/2013; · 3.69 Impact Factor
• Article: Two-Component Signal Transduction System CBO0787/CBO0786 Represses Transcription from Botulinum Neurotoxin Promoters in Clostridium botulinum ATCC 3502.

  Zhen Zhang, Hannu Korkeala, Elias Dahlsten, Elina Sahala, John T Heap, Nigel P Minton, Miia Lindström
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  ABSTRACT: Blocking neurotransmission, botulinum neurotoxin is the most poisonous biological substance known to mankind. Despite its infamy as the scourge of the food industry, the neurotoxin is increasingly used as a pharmaceutical to treat an expanding range of muscle disorders. Whilst neurotoxin expression by the spore-forming bacterium Clostridium botulinum appears tightly regulated, to date only positive regulatory elements, such as the alternative sigma factor BotR, have been implicated in this control. The identification of negative regulators has proven to be elusive. Here, we show that the two-component signal transduction system CBO0787/CBO0786 negatively regulates botulinum neurotoxin expression. Single insertional inactivation of cbo0787 encoding a sensor histidine kinase, or of cbo0786 encoding a response regulator, resulted in significantly elevated neurotoxin gene expression levels and increased neurotoxin production. Recombinant CBO0786 regulator was shown to bind to the conserved -10 site of the core promoters of the ha and ntnh-botA operons, which encode the toxin structural and accessory proteins. Increasing concentration of CBO0786 inhibited BotR-directed transcription from the ha and ntnh-botA promoters, demonstrating direct transcriptional repression of the ha and ntnh-botA operons by CBO0786. Thus, we propose that CBO0786 represses neurotoxin gene expression by blocking BotR-directed transcription from the neurotoxin promoters. This is the first evidence of a negative regulator controlling botulinum neurotoxin production. Understanding the neurotoxin regulatory mechanisms is a major target of the food and pharmaceutical industries alike.
  PLoS Pathogens 03/2013; 9(3):e1003252. · 9.13 Impact Factor
• Article: Sequencing of Virulence Genes Shows Limited Genetic Variability in Yersinia pseudotuberculosis.

  Eveliina Palonen, Susanna Kangas, Panu Somervuo, Miia Lindström, Maria Fredriksson-Ahomaa, Mikael Skurnik, Hannu Korkeala
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  ABSTRACT: Abstract Yersinia pseudotuberculosis is a foodborne pathogen often detected and identified using polymerase chain reaction (PCR) with primers targeted to virulence genes. Sequence variability of the virulence genes in strains representing different serotypes is unknown. Sequence variability could hinder the recognition of this pathogen by PCR and affect the host-pathogen interactions. Sequencing of inv, virF, and yadA of 18 Y. pseudotuberculosis strains showed limited variability of inv and virF, whereas the sequences of yadA varied considerably.
  Foodborne Pathogens and Disease 11/2012; · 2.26 Impact Factor
• Article: Genetic diversity and antimicrobial resistance of Yersinia enterocolitica isolated from pigs and humans in Lithuania.

  Aleksandr Novoslavskij, Eglė Kudirkienė, Audronė Marcinkutė, Almina Bajoriūnienė, Hannu Korkeala, Mindaugas Malakauskas
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  ABSTRACT: BACKGROUND: Yersiniosis is one of the three leading foodborne zoonoses in Lithuania, and the incidence of 12.86 per 100 000 population was the highest among EU member states in 2010. Contaminated pig carcasses and subsequently undercooked pig meat are considered to be the primary transmission vehicle of enteropathogenic Y. enterocolitica to consumers. With the aim of evaluating pigs as a possible source of human yersiniosis in Lithuania, this study investigated the genetic diversity of Y. enterocolitica isolated from pigs and human cases of yersiniosis. In addition, the antimicrobial resistance of selected isolates from both sources was compared. RESULTS: In total, 83 Y. enterocolitica strains were characterised using pulsed field gel electrophoresis. Overall, 68% of Y. enterocolitica 4/O:3 pulsotypes found in human clinical samples were identical to 81% of pulsotypes found in the pig production chain. Yersinia enterocolitica pulsotype II was confirmed as the dominant pulsotype in the pig production chain and was identical to nine of 19 Y. enterocolitica strains found in humans. All tested Y. enterocolitica 4/O:3 strains were resistant to ampicillin and erythromycin and sensitive to ciprofloxacin. Of the strains studied, 5% were resistant to tetracycline and streptomycin. CONCLUSION: This study showed that pigs may be the main source of human yersiniosis in Lithuania. In addition, Y. enterocolitica 4/O:3 strains isolated from the pig production chain and from yersiniosis patients shared similar resistance to different antimicrobials.© 2012 Society of Chemical Industry.
  Journal of the Science of Food and Agriculture 11/2012; · 1.44 Impact Factor
• Article: Prevalence and genetic diversity of enteropathogenic Yersinia spp. in pigs at farms and slaughter in Lithuania.

  Aleksandr Novoslavskij, Loreta Sernienė, Alvydas Malakauskas, Riikka Laukkanen-Ninios, Hannu Korkeala, Mindaugas Malakauskas
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  ABSTRACT: The prevalence of enteropathogenic Yersinia spp. in pigs at farms and slaughter in relation to potential farming risk factors in Lithuania was examined. Pig faeces and carcase swab samples from 11 farms were studied at slaughterhouses. Nine of the 11 farms were visited again 3-5months later, and pooled feacal samples and environmental samples were collected. Pathogenic Yersinia enterocolitica was found in 64% and Yersinia pseudotuberculosis in 45% of the sampled pig farms. All obtained isolates belonged to bioserotypes 4/O:3 and 2/O:3, respectively. Low biosecurity level was associated with a high prevalence of Y. enterocolitica on farms. Characterization with PFGE of 64 Y. enterocolitica and 27 Y. pseudotuberculosis isolates revealed seven and two different genotypes, respectively. Dominant enteropathogenic Yersinia spp. genotypes were obtained in both pig feacal and carcase samples. The high contamination of pig carcases (25%) with enteropathogenic Yersinia spp. may be an important factor contributing to the high incidence of human yersiniosis in Lithuania.
  Research in Veterinary Science 10/2012; · 1.65 Impact Factor
• Source

  Available from: Taurai Tasara

  Article: Phenotypic and transcriptomic analyses of Sigma L-dependent characteristics in Listeria monocytogenes EGD-e.

  Mirjami Mattila, Panu Somervuo, Thomas Rattei, Hannu Korkeala, Roger Stephan, Taurai Tasara
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  ABSTRACT: In this study the phenotypic and transcriptomic traits associated with the alternative sigma factor protein Sigma L in Listeria monocytogenes EGD-e were investigated. It was demonstrated that Sigma L is required for efficient growth in presence of stress associated with food preservative measures such as low temperature and organic acids. Furthermore, besides attenuation of swarming motility, the disruption of Sigma L in this bacterium also reduces resistance to a diverse range of toxic compounds, including some of the antibiotics used in listeriosis treatment. Genes under Sigma L-dependent transcriptional regulation were identified based on comparison of transcriptomes between exponentially growing cells of the EGD-e sigL null mutant and its parental strain cultivated under cold stress (3 °C) and optimized (37 °C) temperature conditions. Four hundred and forty genes under positive Sigma L-dependent transcriptional regulation were identified. The Sigma L regulon as revealed under these conditions comprises genes that code for proteins with diverse cellular functions including protein synthesis, nutrient transport, energy metabolism, cell envelope synthesis, and motility. The diverse range of transcriptome alterations induced by a sigL null mutation is thus consistent with the multiple phenotypic defects observed in the EGD-e ΔsigL mutant. These results demonstrate that Sigma L provides important global transcription regulatory functions in L. monocytogenes EGD-e. These promote execution of various cellular processes and stress adaptation responses thereby enabling this bacterium to overcome various food preservation measures as well as antibiotics and other toxic chemicals.
  Food Microbiology 10/2012; 32(1):152-64. · 3.28 Impact Factor
• Article: Clostridium tyrobutyricum Strains Show Wide Variation in Growth at Different NaCl, pH, and Temperature Conditions.

  Marjo Ruusunen, Anu Surakka, Hannu Korkeala, Miia Lindström
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  ABSTRACT: Outgrowth from Clostridium tyrobutyricum spores in milk can lead to butyric acid fermentation in cheeses, causing spoilage and economical loss to the dairy industry. The aim of this study was to investigate the growth of 10 C. tyrobutyricum strains at different NaCl, pH, and temperature conditions. Up to 7.5-fold differences among the maximum growth rates of different strains in the presence of 2.0% NaCl were observed. Five of 10 strains were able to grow in the presence of 3.0% NaCl, while a NaCl concentration of 3.5% was completely inhibitory to all strains. Seven of 10 strains were able to grow at pH 5.0, and up to 4- and 12.5-fold differences were observed among the maximum growth rates of different strains at pH 5.5 and 7.5, respectively. The maximum growth temperatures varied from 40.2 to 43.3°C. The temperature of 10°C inhibited the growth of all strains, while 8 of 10 strains grew at 12 and 15°C. Despite showing no growth, all strains were able to survive at 10°C. In conclusion, wide variation was observed among different C. tyrobutyricum strains in their ability to grow at different stressful conditions. Understanding the physiological diversity among the strains is important when designing food control measures and predictive models for the growth of spoilage organisms in cheese.
  Journal of food protection 10/2012; 75(10):1791-5. · 1.94 Impact Factor
• Article: Roles of Four Putative DEAD-Box RNA Helicase Genes in Growth of Listeria monocytogenes EGD-e under Heat, pH, Osmotic, Ethanol, and Oxidative Stress Conditions.

  Annukka Markkula, Miia Lindström, Per Johansson, Johanna Björkroth, Hannu Korkeala
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  ABSTRACT: To examine the role of the four putative DEAD-box RNA helicase genes of Listeria monocytogenes EGD-e in stress tolerance, the growth of the Δlmo0866, Δlmo1246, Δlmo1450, and Δlmo1722 deletion mutant strains at 42.5°C, at pH 5.6 or pH 9.4, in 6% NaCl, in 3.5% ethanol, and in 5 mM H(2)O(2) was studied. Restricted growth of the Δlmo0866 deletion mutant strain in 3.5% ethanol suggests that Lmo0866 contributes to ethanol stress tolerance of L. monocytogenes EGD-e. The Δlmo1450 mutant strain showed negligible growth at 42.5°C, at pH 9.4, and in 5 mM H(2)O(2) and a lower maximum growth temperature than the wild-type EGD-e, suggesting that Lmo1450 is involved in the tolerance of L. monocytogenes EGD-e to heat, alkali, and oxidative stresses. The altered stress tolerance of the Δlmo0866 and Δlmo1450 deletion mutant strains did not correlate with changes in relative expression levels of lmo0866 and lmo1450 genes under corresponding stresses, suggesting that Lmo0866- and Lmo1450-dependent tolerance to heat, alkali, ethanol, or oxidative stress is not regulated at the transcriptional level. Growth of the Δlmo1246 and Δlmo1722 deletion mutant strains did not differ from that of the wild-type EGD-e under any of the conditions tested, suggesting that Lmo1246 and Lmo1722 have no roles in the growth of L. monocytogenes EGD-e under heat, pH, osmotic, ethanol, or oxidative stress. This study shows that the putative DEAD-box RNA helicase genes lmo0866 and lmo1450 play important roles in tolerance of L. monocytogenes EGD-e to ethanol, heat, alkali, and oxidative stresses.
  Applied and environmental microbiology 07/2012; 78(19):6875-82. · 3.69 Impact Factor
• Article: Inhibition of Toxigenesis of Group II (Nonproteolytic) Clostridium botulinum Type B in Meat Products by Using a Reduced Level of Nitrite.

  Riikka Keto-Timonen, Miia Lindström, Eero Puolanne, Markku Niemistö, Hannu Korkeala
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  ABSTRACT: The effect of three different concentrations of sodium nitrite (0, 75, and 120 mg/kg) on growth and toxigenesis of group II (nonproteolytic) Clostridium botulinum type B was studied in Finnish wiener-type sausage, bologna-type sausage, and cooked ham. A low level of inoculum (2.0 log CFU/g) was used for wiener-type sausage and bologna-type sausage, and both low (2.0 log CFU/g) and high (4.0 log CFU/g) levels were used for cooked ham. The products were formulated and processed under simulated commercial conditions and stored at 8°C for 5 weeks. C. botulinum counts were determined in five replicate samples of each nitrite concentration at 1, 3, and 5 weeks after thermal processing. All samples were positive for C. botulinum type B. The highest C. botulinum counts were detected in nitrite-free products. Toxigenesis was observed in nitrite-free products during storage, but products containing either 75 or 120 mg/kg nitrite remained nontoxic during the 5-week study period, suggesting that spores surviving the heat treatment were unable to germinate and develop into a toxic culture in the presence of nitrite. The results suggest that the safety of processed meat products with respect to group II C. botulinum type B can be maintained even with a reduced concentration (75 mg/kg) of sodium nitrite.
  Journal of food protection 07/2012; 75(7):1346-9. · 1.94 Impact Factor
• Article: Involvement of two-component system CBO0366/CBO0365 in the cold shock response and growth of group I (proteolytic) Clostridium botulinum ATCC 3502 at low temperatures.

  Miia Lindström, Elias Dahlsten, Henna Söderholm, Katja Selby, Panu Somervuo, John T Heap, Nigel P Minton, Hannu Korkeala
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  ABSTRACT: The role of the two-component system (TCS) CBO0366/CBO0365 in the cold shock response and growth of the mesophilic Clostridium botulinum ATCC 3502 at 15°C was demonstrated by induced expression of the TCS genes upon cold shock and impaired growth of the TCS mutants at 15°C.
  Applied and environmental microbiology 06/2012; 78(15):5466-70. · 3.69 Impact Factor
• Article: Genes encoding putative DEAD-box RNA helicases in Listeria monocytogenes EGD-e are needed for growth and motility at 3°C.

  Annukka Markkula, Mirjami Mattila, Miia Lindström, Hannu Korkeala
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  ABSTRACT: Quantitative RT-PCR revealed that transcripts of all four putative DEAD-box RNA helicase genes of the psychrotrophic pathogen Listeria monocytogenes EGD-e are found at higher levels in organisms grown at 3°C than at 37°C. At 3°C, growth of the three corresponding gene deletion mutants Δlmo0866, Δlmo1450 and Δlmo1722 was clearly restricted. The minimum growth temperatures of the three mutants were also higher than that of the wild-type EGD-e. In addition to inability to grow at 3°C, growth of Δlmo0866 and Δlmo1722 was reduced at 25°C, suggesting special roles of Lmo0866 and Lmo1722 in growth at suboptimal temperatures. Growth of Δlmo1450 was restricted not only at 3°C and 25°C, but also at 37°C, suggesting that Lmo1450 plays a universal role in growth of L. monocytogenes EGD-e. Moreover, cold-sensitive Δlmo0866, Δlmo1450 and Δlmo1722 were impaired in motility. The Δlmo0866 and Δlmo1450 strains were non-motile, while Δlmo1722 showed reduced motility. This study shows that the putative DEAD-box RNA helicase genes lmo0866, lmo1450 and lmo1722 are necessary for cold tolerance and motility of L. monocytogenes EGD-e.
  Environmental Microbiology 05/2012; 14(8):2223-32. · 5.84 Impact Factor
• Article: Involvement of Clostridium botulinum ATCC 3502 sigma factor K in early-stage sporulation.

  David G Kirk, Elias Dahlsten, Zhen Zhang, Hannu Korkeala, Miia Lindström
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  ABSTRACT: A key survival mechanism of Clostridium botulinum, the notorious neurotoxic food pathogen, is the ability to form heat-resistant spores. While the genetic mechanisms of sporulation are well understood in the model organism Bacillus subtilis, nothing is known about these mechanisms in C. botulinum. Using the ClosTron gene-knockout tool, sigK, encoding late-stage (stage IV) sporulation sigma factor K in B. subtilis, was disrupted in C. botulinum ATCC 3502 to produce two different mutants with distinct insertion sites and orientations. Both mutants were unable to form spores, and their elongated cell morphology suggested that the sporulation pathway was blocked at an early stage. In contrast, sigK-complemented mutants sporulated successfully. Quantitative real-time PCR analysis of sigK in the parent strain revealed expression at the late log growth phase in the parent strain. Analysis of spo0A, encoding the sporulation master switch, in the sigK mutant and the parent showed significantly reduced relative levels of spo0A expression in the sigK mutant compared to the parent strain. Similarly, sigF showed significantly lower relative transcription levels in the sigK mutant than the parent strain, suggesting that the sporulation pathway was blocked in the sigK mutant at an early stage. We conclude that σ(K) is essential for early-stage sporulation in C. botulinum ATCC 3502, rather than being involved in late-stage sporulation, as reported for the sporulation model organism B. subtilis. Understanding the sporulation mechanism of C. botulinum provides keys to control the public health risks that the spores of this dangerous pathogen cause through foods.
  Applied and environmental microbiology 04/2012; 78(13):4590-6. · 3.69 Impact Factor
• Article: Piglets are a source of pathogenic Yersinia enterocolitica on fattening-pig farms.

  Sonja Virtanen, Laura Salonen, Riikka Laukkanen-Ninios, Maria Fredriksson-Ahomaa, Hannu Korkeala
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  ABSTRACT: To study the origin and spread of Yersinia enterocolitica among pigs, fecal and blood samples were repeatedly taken on a fattening farm. A few piglets were found to be already infected on breeding farms. After the piglets were mixed, the infection spread through the whole unit. Eventually, all the pigs excreted the pathogen.
  Applied and environmental microbiology 02/2012; 78(8):3000-3. · 3.69 Impact Factor
• Article: Comparative Genomic Hybridization Analysis Shows Different Epidemiology of Chromosomal and Plasmid-Borne cpe-Carrying Clostridium perfringens Type A.

  Päivi Lahti, Miia Lindström, Panu Somervuo, Annamari Heikinheimo, Hannu Korkeala
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  ABSTRACT: Clostridium perfringens, one of the most common causes of food poisonings, can carry the enterotoxin gene, cpe, in its chromosome or on a plasmid. C. perfringens food poisonings are more frequently caused by the chromosomal cpe-carrying strains, while the plasmid-borne cpe-positive genotypes are more commonly found in the human feces and environmental samples. Different tolerance to food processing conditions by the plasmid-borne and chromosomal cpe-carrying strains has been reported, but the reservoirs and contamination routes of enterotoxin-producing C. perfringens remain unknown. A comparative genomic hybridization (CGH) analysis with a DNA microarray based on three C. perfringens type A genomes was conducted to shed light on the epidemiology of C. perfringens food poisonings caused by plasmid-borne and chromosomal cpe-carrying strains by comparing chromosomal and plasmid-borne cpe-positive and cpe-negative C. perfringens isolates from human, animal, environmental, and food samples. The chromosomal and plasmid-borne cpe-positive C. perfringens genotypes formed two distinct clusters. Variable genes were involved with myo-inositol, ethanolamine and cellobiose metabolism, suggesting a new epidemiological model for C. perfringens food poisonings. The CGH results were complemented with growth studies, which demonstrated different myo-inositol, ethanolamine, and cellobiose metabolism between the chromosomal and plasmid-borne cpe-carrying strains. These findings support a ubiquitous occurrence of the plasmid-borne cpe-positive strains and their adaptation to the mammalian intestine, whereas the chromosomal cpe-positive strains appear to have a narrow niche in environments containing degrading plant material. Thus the epidemiology of the food poisonings caused by two populations appears different, the plasmid-borne cpe-positive strains probably contaminating foods via humans and the chromosomal strains being connected to plant material.
  PLoS ONE 01/2012; 7(10):e46162. · 4.09 Impact Factor
• Article: Requirement for RNA helicase CsdA for growth of Yersinia pseudotuberculosis IP32953 at low temperatures.

  Eveliina Palonen, Miia Lindström, Panu Somervuo, Per Johansson, Johanna Björkroth, Hannu Korkeala
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  ABSTRACT: The expression of csdA, encoding an RNA helicase, was induced at 3°C in Yersinia pseudotuberculosis. The role of CsdA in Y. pseudotuberculosis under cold conditions was confirmed by impaired growth of insertional csdA mutants at 3°C. The results suggest that CsdA is crucial for Y. pseudotuberculosis survival in the chilled food chain.
  Applied and environmental microbiology 12/2011; 78(4):1298-301. · 3.69 Impact Factor
• Article: Analysis of Clostridium botulinum serotype E strains by using multilocus sequence typing, amplified fragment length polymorphism, variable-number tandem-repeat analysis, and botulinum neurotoxin gene sequencing.

  Thomas E Macdonald, Charles H Helma, Yulin Shou, Yolanda E Valdez, Lawrence O Ticknor, Brian T Foley, Stephen W Davis, George E Hannett, Cassandra D Kelly-Cirino, Jason R Barash, Stephen S Arnon, Miia Lindström, Hannu Korkeala, Leonard A Smith, Theresa J Smith, Karen K Hill
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  ABSTRACT: A total of 41 Clostridium botulinum serotype E strains from different geographic regions, including Canada, Denmark, Finland, France, Greenland, Japan, and the United States, were compared by multilocus sequence typing (MLST), amplified fragment length polymorphism (AFLP) analysis, variable-number tandem-repeat (VNTR) analysis, and botulinum neurotoxin (bont) E gene sequencing. The strains, representing environmental, food-borne, and infant botulism samples collected from 1932 to 2007, were analyzed to compare serotype E strains from different geographic regions and types of botulism and to determine whether each of the strains contained the transposon-associated recombinase rarA, involved with bont/E insertion. MLST examination using 15 genes clustered the strains into several clades, with most members within a cluster sharing the same BoNT/E subtype (BoNT/E1, E2, E3, or E6). Sequencing of the bont/E gene identified two new variants (E7, E8) that showed regions of recombination with other E subtypes. The AFLP dendrogram clustered the 41 strains similarly to the MLST dendrogram. Strains that could not be differentiated by AFLP, MLST, or bont gene sequencing were further examined using three VNTR regions. Both intact and split rarA genes were amplified by PCR in each of the strains, and their identities were confirmed in 11 strains by amplicon sequencing. The findings suggest that (i) the C. botulinum serotype E strains result from the targeted insertion of the bont/E gene into genetically conserved bacteria and (ii) recombination events (not random mutations) within bont/E result in toxin variants or subtypes within strains.
  Applied and environmental microbiology 12/2011; 77(24):8625-34. · 3.69 Impact Factor
• Article: Growth of group II Clostridium botulinum strains at extreme temperatures.

  Yağmur Derman, Miia Lindström, Katja Selby, Hannu Korkeala
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  ABSTRACT: The minimum and maximum growth temperatures and the maximum growth rates at 10, 30, 37, and 40°C were determined for 24 group II Clostridium botulinum strains. Genetic diversity of the strains was revealed by amplified fragment length polymorphism (AFLP) analysis. The minimum growth temperatures ranged from 6.2 to 8.6°C, and the maximum growth temperatures ranged from 34.7 to 39.9°C. The mean maximum growth temperatures and mean maximum growth rates of type E strains at 37°C were significantly higher than those of type B and type F strains. A significant correlation between maximum growth rates at 37°C and maximum growth temperatures was found for all strains. Some type E strains with a high minimum growth temperature also had a higher maximum growth rate at 37°C than at 30°C, which suggests that some group II C. botulinum strains are more mesophilic in their growth properties than others. We found relatively small differences between AFLP clusters, indicating that diverse genetic background among the strains was not reflected in the growth properties. The growth characteristics of group II C. botulinum and some type E strains with mesophilic growth properties may have an impact on inoculation studies and predictive modeling for assessing the safety of foods.
  Journal of food protection 11/2011; 74(11):1797-804. · 1.94 Impact Factor
• Source

  Available from: Carina Brehony

  Article: Population structure of the Yersinia pseudotuberculosis complex according to multilocus sequence typing.

  Riikka Laukkanen-Ninios, Xavier Didelot, Keith A Jolley, Giovanna Morelli, Vartul Sangal, Paula Kristo, Carina Brehony, Priscilla F M Imori, Hiroshi Fukushima, Anja Siitonen, Galina Tseneva, Ekaterina Voskressenskaya, Juliana P Falcao, Hannu Korkeala, Martin C J Maiden, Camila Mazzoni, Elisabeth Carniel, Mikael Skurnik, Mark Achtman
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  ABSTRACT: Multilocus sequence analysis of 417 strains of Yersinia pseudotuberculosis revealed that it is a complex of four populations, three of which have been previously assigned species status [Y. pseudotuberculosis sensu stricto (s.s.), Yersinia pestis and Yersinia similis] and a fourth population, which we refer to as the Korean group, which may be in the process of speciation. We detected clear signs of recombination within Y. pseudotuberculosis s.s. as well as imports from Y. similis and the Korean group. The sources of genetic diversification within Y. pseudotuberculosis s.s. were approximately equally divided between recombination and mutation, whereas recombination has not yet been demonstrated in Y. pestis, which is also much more genetically monomorphic than is Y. pseudotuberculosis s.s. Most Y. pseudotuberculosis s.s. belong to a diffuse group of sequence types lacking clear population structure, although this species contains a melibiose-negative clade that is present globally in domesticated animals. Yersinia  similis corresponds to the previously identified Y. pseudotuberculosis genetic type G4, which is probably not pathogenic because it lacks the virulence factors that are typical for Y. pseudotuberculosis s.s. In contrast, Y. pseudotuberculosis s.s., the Korean group and Y. pestis can all cause disease in humans.
  Environmental Microbiology 09/2011; 13(12):3114-27. · 5.84 Impact Factor
• Article: Listeria monocytogenes serotypes 1/2c and 3c possess inlH.

  Annukka Markkula, Miia Lindström, Hannu Korkeala
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  ABSTRACT: To examine the serotype specificity of inlH, which encodes the virulence-associated surface protein InlH related to the intracellular survival of Listeria monocytogenes in mice, the presence of inlH in 337 L. monocytogenes strains, representing 11 different serotypes, was studied. A total of 106 strains representing 3 serotypes and 14 pulsed-field gel electrophoresis (PFGE) types were positive for inlH by polymerase chain reaction. inlH was present in all 99 serotype 1/2c and 3 serotype 3c strains. Moreover, 4 out of 129 (3%) serotype 1/2a strains carried inlH. All 106 strains representing serotypes 1/2b, 3a, 3b, 4a, 4b, 4c, 4d, and 7 and 125 out of 129 (97%) serotype 1/2a strains were inlH-negative. The coding sequences of the inlH genes of eight L. monocytogenes strains representing three serotypes and five PFGE types were identical. These results suggest that inlH is specifically present in serotype 1/2c, 3c, and a small fraction of 1/2a L. monocytogenes strains and exists as a single allele.
  Foodborne Pathogens and Disease 06/2011; 8(10):1125-9. · 2.26 Impact Factor