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  • cspB- ja cspC-geenien merkitys Clostridium botulinum ATCC 3502 -kannan kyvylle kasvaa kylmässä 
    Norrgård, Heidi (University of HelsinkiHelsingin yliopistoHelsingfors universitet, 2009)
    Clostridium botulinum is an anaerobic rod shaped bacterium. It forms endospores that are commonly found in soils and aquatic sediments. C. botulinum produces one of the most potent neurotoxins that causes dangerous neuroparalytic disease called botulism. Food-borne botulism is an intoxication due to ingestion of preformed neurotoxin in foods. When favouring minimally processed food which safety depends almost only on chilled storage the risk of neurotoxin formation increases. It is essential to know the mechanisms of cold tolerance of C. botulinum when improving the safety of high-risk foods. A rapid temperature downshift causes decrease in the synthesis of most of the proteins in the cell. However the synthesis of structurally related cold shock proteins (Csp) reaches the maximum level after cold shock. It is assumed that these proteins are important for bacterial cold shock response. The exact function and meaning of cold shock proteins is not fully understood but they are believed e.g. to inhibit the formation of unwanted secondary structures of nucleic acids and regulate the synthesis of other proteins. The genome of C. botulinum ATCC 3502 strain contains three cold shock protein coding genes: cspA, cspB and cspC. The meaning of the cold shock proteins for the growth of ATCC 3502 was studied by comparing the growth of wild type strain and cspB- and cspC -mutant strains at different temperatures. The alterations in the expression of cspA-, cspB- and cspC -genes after cold shock were also studied. The results confirm that cspB and cspC genes are related to cold tolerance of the C. botulinum ATCC 3502 strain. cspB and cspC mutant strains grew at 20 °C at a reduced rate compared to C. botulinum ATCC 3502 wild type strain. There was no difference in growth rate between the strains grown at 37 °C and 44 °C. With quantitative RT-PCR, a significant twofold increase in the expression of cspA and cspB was detected for C. botulinum ATCC 3502 wild type strain while the expression of cspC stayed at normal level after cold shock. In cspB mutant strain the expression of cspA increased almost fivefold after cold shock. In cspC mutant strain after cold shock the trend of the expression of the other csp-genes was to decrease or stay at normal level. The results of quantitative RT-PCR method indicate some ability of csp genes to compensate for the functions of down regulated csp gene by other csp genes.
  • Maidon alkutuotantoympäristöstä eristettyjen Listeria monocytogenes -kantojen happamuuden, emäksisyyden ja pesuaineiden kestävyys 
    Koskensalo, Sirja (2018)
    Listeria monocytogenes is a gram-positive, non-sporeforming, rod-shaped bacterium, a human and animal pathogen and a food-borne pathogen/agent. Listeriosis, caused by L. monocytogenes, can be a serious disease and even cause death. L. monocytogenes is a major risk factor for the microbiological quality of foodstuffs, and a pathogen especially for those in risk groups. The aim of this study was to investigate sporadic and persistent strains of L. monocytogenes, isolated in a milk-production environment, and their growth in acidic and alkaline environments, as well as in environments containing the detergents Basix and Cidmax, and to investigate eventual differences between these strains. The features and occurrence of L. monocytogenes, its capability to resist stress and listeriosis are discussed in the literature part of this thesis. In this study it was found that bacteria were able to grow in the environments tested, in the concentrations used. No statistically significant differences between the strains were discovered. All investigated L. monocytogenes strains grew in pH 5.6, pH 9.0 and in liquids containing the detergents Cidmax and Basix. In acidic conditions, the majority of the strains grew similarly to reference strain EGD-e. Strain E3 started its exponential growth faster than the other strains. In acidic conditions strain D3 had the highest growth rate (30.06). The strains that grew the most weakly in acidic conditions were B3 and reference strain ATCC 19115. In alkaline conditions and in Cidmax-BHI liquid, the most of L. monocytogenes strains grow similarly to reference strain EGD-e. Strains E3 and D3 grew faster than other strains in alkaline conditions and Cidmax-BHI liquid and strains B3 and ATCC 19115 grew slower than the other strains. In Basix-BHI liquid, the strains of L. monocytogenes grew mainly similarly to each other, and these strains grew a little faster than reference strain EGD-e. Compared to the other strains, strain E3 grew the fastest and strains B3 and ATCC 19115 grew slower than the other strains. In this study, differences in stress tolerance between L. monocytogenes strains were found. In future, the results of this study may be utilized in genomic association research where geno- and phenotypes are compared to each other. This could produce new information on the development of stress tolerance of L. monocytogenes strains with different genomes and phenotypes.

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HELSINGIN YLIOPISTO