Bacterial-Pathogenicity

Bacterial-Pathogenic - Bacterial pathogenicity Parasite versus host defence Microorganisms evolution The tendency of the living organisms to seize

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Bacterial pathogenicity Parasite versus host defence
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Microorganisms’ evolution The tendency of the living organisms to seize new environments. The microorganisms succeeded. “The bacteria have been trying for almost 2 milliard years to become two from one, in the shortest possible period of time, the most economical possible and in varied conditions.” (François Jacob)
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Microorganisms’ evolution We have appeared, evolved and survived in a world dominated by microorganisms. Microorganisms, biological factor of our environment. A continuos history: microbial virulence & antimicrobial defense mechanisms of the host.
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Characteristics of the parasitism Loss of structures that ensure independent life. Auxotrophs versus prototrophs. Some microorganisms can synthesize by themselves all the aminoacids and they are called prototrophs . Auxotrophs have lost, by mutation, a biosynthetic ability.
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Appearance and development of structures and functions that ensure: penetration in the host; maintenance , survival and multiplication; invasion of the host; survival of the parasite in nature: between two hosts, under the pressure of the immune response of the host.
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Microbial pathogenicity Virulence factors are characteristics that enable bacteria to cause disease. Pathogenic bacteria may have one or several virulence factors. They may be common to all bacteria of a given genus or species, or they may be a characteristic of special pathogenic strains.
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Microbial pathogenicity Virulence factors that are common to the genus or species appear to give the organism a survival advantage ; they may be selected during evolution. Those that are unique to some strains are usually acquired through mechanisms of genetic exchange (generally conjugation and transduction) and are not associated with specific survival advantage for the bacterium.
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Virulence Expresses the pathogenicity degree of a microorganism and is expressed in MLD (minimum letal dose) and, more precise, in LD50 (letal dose 50% - amount of Ag that kill 50% of inoculated animals). The precise measurement of virulence and the cloning of bacterial DNA allowed identification of virulence factors and their codifying genes.
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The molecular Koch’s postulates The investigated phenotype (property, structure, function) has to be associated to pathogenic strains of a species or to pathogenic species of a genus. The specific inactivation of the gene(s) that codify the suspected pathogenic phenotype has to lead to quantifiable loss of virulence. Reversion or allelic substitution of the mutant gene has to restore virulence. Def: different forms of a new gene that appeared after mutation = allel and they have the some place as first (original) gene
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Virulence by genetic mutation
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Penetration in the host Through breaks in the covering mucus of secretor epithelia. Translocation
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This note was uploaded on 10/18/2010 for the course BIO 204 taught by Professor O'neal during the Fall '07 term at SUNY Stony Brook.

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Bacterial-Pathogenic - Bacterial pathogenicity Parasite versus host defence Microorganisms evolution The tendency of the living organisms to seize

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