What makes a Pathogen? Flashcards
Define a pathogen
An organism that can cause disease in animals and plants
Define virulence
Relative ability to cause disease
Degree of pathogenicity
Virulence Factors
Determinants that cause damage to the cell or are required for the survival of the pathogen in the host
Define enteric pathogen
A pathogen that resides in the GIT
Define an obligate intracellular pathogen
A pathogen that lives exclusively within the hot and depends on the host for survival
Define a fastidious intracellular pathogen
A pathogen that lives within the host and has stringent growth requirements
Properties that cause disease
- VF
- pathogenicity islands
- toxins
Possible infection outcomes
- clearance
- homeostatic interaction
- disease
Assumptions about TB
- ineffective immune response underlies disease progression
- lesion are homogenous
- inactive and active lesions have very different bacterial burdens
Define genetics
- the study of individual genes, their functions, and roles
Define genome
The complete genetic repository of an organism
Define genomics
- The study and use of complete genome sequences
Emerging themes in microbiology
- genome organisation, composition and diversity
- horizontal gene transfer
- genome decay among obligate intracell. pathogens
- phase and antigenic variation among mucosal pathogens
Things that affect genome organization, composition and diversity
- wide variation of genome organization
- high percentage of predicted gene encode proteins of unknown function
- variability in GC content between organisms
Define HGT
The transfer of DNA, frequently cassettes of genes, between organsims
Mechanisms of HGT
- transformation (plasmids)
- conjugation (transposons)
- transduction (phages)
- genomic recombination
Describe reductive, convergent evolution
Prolonged intracellular lifestyle leads to loss of genes not needed for life in the host
Examples of organisms that exhibit genome decay and host adaptation
- Rickettsia prowazekii
- Chamydia trachomatis
- Treponema pallidum
What is phase variation?
Reversible high-frequency gain and loss of a phenotype resulting from changes of expression of single and multiple genes
- Salmonella flagellin
What is antigenic variation?
- variation of surface structure by pathogens
mutation, recombination, switching
Why do organisms use phase and anitgenic variation?
to avoid detection or outpace a host’s immune system
Mechanisms of phase variation in N meningitidis
Tandem repeats in promoter sequences affect:
- transcription
- translation
- replication
Define core genome
- all the genes that each member of a species possesses
Define distributed genes
All the genes that are not shared by all the strains of a species
Define a supragenome
Core genome plus all of the distributed genes of a species
Define a symbiome
The organismal ecosystem complete with the eukaryotic host and all of its assicated microbiomes
Define hologenome
The symbiome’s genome
Basic tenets of the damage-response framework
- pathogenesis is an outcome of an interaction between a host and a microorganism
- the host-relevant outcome of this host-microorganism interaction is determined by the amount of damage to the host
- host damage can result from microbial factors and/or host repsonse
Describe levels of graph of damage-response framework
- death
- disease
- latency
- colonization
- commensalism
