micro 4 Flashcards
how do microbial communities vary?
vary by site on the body
- environmental conditions and nutrient availability
where is there a high and a low bacterial density in the GI tract?
high= colon (large intestine) low= small intestine and stomach
what is the ph in the small intestine, stomach and colon?
small intestine- 6.5-7.5
stomach-1-2
colon 5-7
what is the aerobica conditions like in the small intestines, stomach and colon?
small intestine= dec oxygen content
stomach= oxygen present
solon= anaerobic
what part of the GI tract has the largest and the smallest bacterial density?
smallest= stomach -10^1-3
largest=colon 10^10-13
what is the bacterial diversity like in the small intestine?
- Low bacterial diversity
- Facultative anaerobes
- Streptococcus, Lactobacillus, Enterobacteriaceae
what is the bacterial diversity like in the stomach?
- Relatively low bacterial diversity
* Mainly Streptococcus and Lactobacillus
what is the bacterial diversity like in the colon?
- High bacterial diversity
- Particularly anaerobes
- Clostridia
- Bacteriodes
- Bifidobacterium
why do we need a gut microbiome?
when healthy a balance between good and bad microorganisms is maintained which help protect against infectious deiseaes
- they also contribute to metabolism
how does a good microbiome contribute to metabolism?
provides certain nutrients which humans cannot provide normally
- •Breakdown of non-digestible substrates (e.g. dietary fibre and intestinal mucus)•Production of short chain fatty acids (e.gacetate, propionate and butyrate)
•Amino acid metabolism (e.g. Tryptophan)
•Vitamin production (e.gB10; para-aminobenzoic acid)
is the GI of a foetus sterile?
it was assumed so- but there is data to suggest that it maternal microbes can eneter fetus GI tract- seen in first meconium (poo)
what is GI tract microbiota and gestational age related to?
associated with gut microbiota abundance and diversity
how is type of birth linked to difference in initial microbiome?
- vaginal birth derived from vaginal microbiome
- caesarean section derived from maternal skin(e.g. Staphylococcus, Propionibacterium)
what is the core microbiome for gestation/ parturation, infancy, puberty, adulthood, old age?
1- facultative anaerobes, proteobacteria 2-bacteroides, bifidobacterial 3- firmicutes, Bacteroides 4-bacteroides, firmicutes 5- obligate and facultative anaerobes
what are probiotics?
they are a chemical substrate that is selectively used by a host microorganism to produce a healthy benefit
what criterial do prebiotics have to meet?
- Non digestible and resistant to breakdown by stomach acid and human enzymes
- Selectively fermented by intestinal microorganisms
- Selectively target and stimulate growth/activity of beneficial bacteria
what are bacterial targets for prebiotic substrates?
Bifidobacteria and Lactobacilli
are all prebiotics fibre?
yes but not all fibre is prebiotic
what are probiotics?
re live cultures of miroorganisms promoted with health benefits claims;
what are 2 examples of probiotic microbacteria?
•Lactobacilli and bifidobacteria
how do probiotics work?
a- co-aggregation b-biocirfactant production c- bacteiocin and H2O2 production d-signalling effects e-competitive exclusion f-immunomodulation g-modulation of tight junctions
do probiotics work?
high quality evidence but not scientificially proven- states that they are not intended
to diagnose, treat, cure, or prevent any disease.
how is gut microflora disrupted by antibiotics?
•Susceptible cells killed indiscriminately
what can misuse of antibiotics lead to in gut microflora?
- Growth of resistant subpopulation
- Removal of repressing microorganisms
- Lead to secondary infections
how long aprox does it take for gut microflora to return to normal after antibiotics?
40 days-some still missing
composition still different
what is faecal microbial transplants?
- Basic idea is to transplant faecal microbes from healthy individual to a recipient
- Usually taken from parent/partner etc
- Can also be autologous
- Needs to be screened for pathogens!•Has been used to treat patients with CDI
what non-infectious diseases has gut-microbiome been linked to?
obesity
depression
how is helicobacter pylori linked to gut microbiota?
- linked to stomach ulcers/peptic ulcer disease
- risk factor for gastric cancer
what type of bacteria is h.pylori?
gram negative, curved rod, microaerophilic
what strains of h.pylori have a pathogenicity island?
CagPAI
- 40kn of DNA encoding for 31 genes
absent from non-pathogenetic strains
how do h.pylori survive and colonise?
- Uses flagella to swim into the mucus lining
- Breaks down urea
- Sticks tightly to stomach epithelial cells
does h.pylori perfer a more acidic or basic environment?
perfers less acidic- swim away using flagella
how does h.pylori produce urease?
produces urease
creates a bufffer zone of higher ph
its also toxic
may help recruit neutrophils to mucosa
what happens when T4SS from cagPAI injects Cag into GEC cytosol?
- Once inside its phosphorylated by Srcand Ablkinases
- Interacts with host cell proteins with have SH2 domains
- Produces cytoskeleton rearrangement
- Deregulates some signal transduction pathways
how commmon is CAGA?
is the 4thmost abundant protein produced by H. pylori
•Suggests that large amounts needed to have an effect
what is cagA associated with?
•Associated with ↑ Inflammation and more severe disease outcomes
what role does VACA play?
- Vacuolating cytotoxin (VacA) hypothesised in 1988
* Proteinaceous component of H. pyloriculture supernatant vacuolated cultured eukaryotic cells
where is vacA present?
A single intact vacAgene present in all H. pylori strains
•Also present in H. cetorumstrains
what does vacA do in cells?
- Can enter cells but doesn’t have enzymatic activity
- Can form anion selective membrane channels
- Cl-, HCO3-, small organics
- Can potentially cause cell death by altering mitochondria
how can vacA affect the immune system?
- Inhibits activation of T and B-cells
- Impaired macrophage engulfment
- Can stimulate expression of COX-2 in macrophages and neutrophils (↑ proinflammatory)
how do you diagnose h.pylori?
serology urea breath test faecal antigen testing rapid urease test histology
how do you treat h.pylori?
- PPI
- Antibiotics
- No penicillin allergy: Amoxicillin AND either clarithromycin or metronidazole
- Penicillin allergy: Clarithromycin AND metronidazole
what are gut virome?
- These viruses have a role to play
- Vectors for gene transfer
- Non-host based antibacterial defence
what are examples of pro and euk gut vurome?
- Prokaryotic(e.g. CrAssphage and Microviridae bacteriophages). THESE MAKE UP THE MAJORITY •Eukaryotic
- Commensal viruses which can cause disease (e.g. Adenoviridae)•Disease causing (e.g. Rotavirus in some individuals)
