Background info + the microbiota Flashcards
themes common to bacterial pathogen - host interactions (21 cards)
Commensalism:
An association between two organisms in which one benefits and the other derives neither benefit nor harm
Mutualism:
A symbiotic relationship in which both organisms benefit.
What are opportunistic Bacteria?
Bacteria that operate as commensals but under certain conditions will act parasitically.
What are Koch’s postulates?
4 criteria that must be met to identify the etiological (disease causing) agent of disease.
What are the 4 Koch’s postulates:
- (ABUNDANCE / ASSOSCIATION) Microorganism must be found in abundance in all organisms suffering from the disease
- (ISOLATION) The microorganism must be isolated from the infected and grown as a pure culture
- (CAUSING) The cultured microorganism causes disease in healthy organisms
- (REISOLATION / IDENTITY VERIFICATION) The microorganism must be re-isolated from diseased host and identified as identical to the original causative agent
What are the 3 molecular Koch’s Postulates (by Stan Falkow)?
- (ASSOCIATION) Phenotype or property under investigation is associated with pathogenic members of genus or strains of a species
- (DEACTIVATION = LOSS / DECREASE OF DISEASE) Specific inactivation of the gene associated with suspected virulence trait leads to a measurable loss of pathogenicity or virulence
- (RESTORED GENE RESTORES PATHOGENICITY) Reversion of allele replacement of the mutated gene leads to restoration of pathogenicity
What example method following the 3 molecular postulates (TEMPLATE):
Investigate the phenotype of a wild type strain, knockout(via mutagenesis) , and restored strain (via complementation).
Tetanus Toxin: Virulence Factor
Lethal Dose 50 of 2,5ng/ kg -> clostridial neurotoxin that causes rigid paralysis leading to death by asphyxiation.
Prevent the reuptake of neurotransmitters -> preventing breathing is beneficial as the Clostridium is anaerobic, and performs better when there’s less oxygen in the blood.
OmpA: Virulence Factor
Dominant E.coli outer membrane protein -> essential for evasion of macrophage killing and invasion of the blood-brain barrier -> it is also an essential gene with an unknown housekeeping role.
What is the Microbiota:
The complex microbial community that inhabits a particular environmental niche (the different species occupying the niche)
What is the Microbiome:
The combined genetic material / potential of the microbiota (genetic diversity rather than species diversity)
Why is it difficult to culture a human’s microbiota?
There exist many niches across a human’s body, and many species found in these niches have growth conditions not reproducible in the lab
How is the human microbiota studied?
Molecular Biology techniques -> the genetic study of the microbiome by metagenomics (16S rRNA and Shotgun seq)
Factors affecting the Microbiome
Age
Diet <- Socioeconomic and Culture
Health-status
Antibiotics
What is the issue with Microbiota data being presented using principle component analyses?
Recent concerns have been raised about the validity of results reported in the population genetics literature and related fields that place a disproportionate reliance upon PCA outcomes and the insights derived from them. PCA may have a biasing role in genetic investigations.
How are samples from the colon collected?
Faecal Samples are used
Implications of the Kitome:
When investigating the presence of microbial DNA at very low volumes (more sterile surfaces/ niches), there will often be extra DNA present, this contaminant DNA is associated with the kit used in the investigation -> leading to false positives at low levels of wanted DNA.
Effect of the Kitome on the investigation of the gut microbiome:
When sequencing a sample of faeces, the sample bacteria will outnumber the contaminant by the millions, and-so the kitome has little impact on the results.
What is meant by the Kitome?
The microorganisms associated with lab equipment.
How does the gut microbiota differ from person to person?
(DIFFERENT SPECIES SAME FEATURES) The phyla (species make up) varies heavily between individuals, although there are some common groups present in all. Metagenomic analysis reveals the genetic potential of metabolic pathways (metabolic potential) is conserved. Therefore the gut selects for metabolic potential rather than phyla.
Evolution of characterising microbiota:
Before 2018 it was thought that 90% of the gut bacteria could not be cultured, 2018 a lab identified all species present in mice microbiota via sequencing, and culture every species that was identified. This has allowed for culturing of microbiota components aiding determined microbiota transfusions and allowing more diverse methods of investigating virulence.
