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Mechanisms of bacterial persistence and clinical significance
Smělíková, Eva ; Melter, Oto (advisor) ; Pinkas, Dominik (referee)
Persistent bacteria, shortly persisters, are cells that are characterized by their tolerance to antibiotics without containing resistance genes. These are not resistant bacteria, because resistant bacteria are determined by genetic code. Persisters are indistinguishable from other antibiotic sensitive bacteria, and they are rather transient phenotypic subpopulations. Probably all types of bacteria can create a persistent stage, the ability is not species-bound and persistence has been described in a number of bacterial species. The reason for the formation of persistence may be sudden stress, then it is induced formation, or the reason may be an insurance for the future, then we call it stochastic phenotypic variability. Then a variety of phenotypes of different subpopulations within a genetically uniform population can be distinguished. They differ in growth properties and tolerance to antibiotics. Bet-hedging strategy is a hypothesis that describes persistence as insurance against the risk of external fluctuations. During stress an alarmon guanosine tetraphosphate or guanosine pentaphosphate is accumulated to alert the cell to unfavorable conditions and it initiates transition to a more tolerant state. The existence of these tolerant subpopulations is important in recurrent diseases because small...
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Heterogeneity of expression of virulence factors of Salmonella.
Mathéová, Paulína ; Černý, Ondřej (advisor) ; Lichá, Irena (referee)
The emergence of phenotypically heterogeneous individuals within an isogenic bacterial population is considered to be an important adaptation to the host environment. It allows survival of some bacterial subpopulations under diverse stress conditions caused by the host immune system, the emergence of a "division of labor" and cooperation between individual bacteria. Bacteria of the genus Salmonella are important pathogens in humans and livestock. Many of the key virulence factors of Salmonella are heterogeneously expressed. The phenotypic diversity of individual bacteria allows certain individuals to escape the host's immune system and ensure that the gene pool is preserved to future generations. In case when change in conditions causes complete extinction of part of the Salmonella population from the environment, the remaining individuals are able to restore the size of the population and phenotypic diversity, after overcoming unfavourable conditions. This work summarises the knowledge about heterogeneity of expression of virulence factors of Salmonella and the characteristics of individual subpopulations in different environmental conditions. Keywords: Salmonella, heterogeneity, virulence factors, bet-hedging, division-of-labor, bacterial subpopulations.
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Mechanisms of bacterial persistence and clinical significance
Smělíková, Eva ; Melter, Oto (advisor) ; Pinkas, Dominik (referee)
Persistent bacteria, shortly persisters, are cells that are characterized by their tolerance to antibiotics without containing resistance genes. These are not resistant bacteria, because resistant bacteria are determined by genetic code. Persisters are indistinguishable from other antibiotic sensitive bacteria, and they are rather transient phenotypic subpopulations. Probably all types of bacteria can create a persistent stage, the ability is not species-bound and persistence has been described in a number of bacterial species. The reason for the formation of persistence may be sudden stress, then it is induced formation, or the reason may be an insurance for the future, then we call it stochastic phenotypic variability. Then a variety of phenotypes of different subpopulations within a genetically uniform population can be distinguished. They differ in growth properties and tolerance to antibiotics. Bet-hedging strategy is a hypothesis that describes persistence as insurance against the risk of external fluctuations. During stress an alarmon guanosine tetraphosphate or guanosine pentaphosphate is accumulated to alert the cell to unfavorable conditions and it initiates transition to a more tolerant state. The existence of these tolerant subpopulations is important in recurrent diseases because small...
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Influence of experimental conditions on hatching of diapausing stages of the cladoceran Daphnia obtusa
Sailerová, Martina ; Petrusek, Adam (advisor) ; Vaníčková, Ivana (referee)
Diapause is often an adaptation for survival during periods of harsh environmental conditions. Some diapausing stages do not terminate the dormancy once the favourable conditions are restored. Such prolonged diapause may be enforced by environment if a diapausing stage cannot be reached by the cues inducing termination of dormancy. However, it may also be an advantageous bet-hedging strategy to allow only a fraction of dormant stages produced in any given season to hatch the next time conditions become favourable. I tested whether such strategy can be observed in hatching patterns of dormant eggs of Daphnia obtusa - a cladoceran occurring in small Central European temporary waters. I investigated the influence of intensity of illumination on hatching success, and effect of isolating the eggs encased in ephippia from the sediment. Fraction of eggs terminating diapause, fraction of embryos successfully leaving the egg membranes, and timing of the response were assessed at 15 ˚C under four intensities of illumination (100% = 35µmol.m2 .s-1 , 75%, 50%, 25%; photoperiod 12h light: 12h dark) and in complete darkness for 21 days. My results support previous suggestions that there is no genetically-fixed bet-hedging strategy in D. obtusa. I observed high proportion of eggs which terminated diapause in all...
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