MUDr. Dana Maňasková


Vyhledávání na medicinman.cz
 

nemoci-sympt/GASTROENTEROLOGIE/sibo/druhy-sibo

SIBO

Syndrom bakteriálního přerůstání

Syndrome of intestinal bacterial overgrowth

  • Je léčitelné onemocnění, ale někdy se po vyléčení může znovu vrátit
  • Pokud je SIBO způsobeno jiným onemocněním, je třeba nejprve vyléčit toto onemocnění, jinak může být léčba neefektivní.



Acetogens

  • Acetate is produced via a number of microbial metabolic pathways
  • V.s. via reductive acetogenesis
    • 4H2+2CO2›CH3COO-+H++2H2O
  • Reductive acetogenesis - Wood-Ljungdahl metabolic pathway - “homoacetogenesis”
  • Homoacetogenesis
    • Formation of acetate as the sole reduced end product in the metabolism of a substrate
    • “production of more than 2 mol of acetate per mol of sugar consumed”
  • Acetogen is restricted to bacteria producing acetate via the Wood-Ljungdahl pathway
    • Excludes the incomplete oxidizers of SCFAs among the SRB
      • Are acetate producers when feeding on organic molecules such as lactate, but do not perform reductive acetogenesis.
  • Culturing the hydrogen producer Ruminococcus albus with a GIT acetogen
    • Acetate levels in co-culture of around three times that recorded for R. albus alone
    • Hydrogen was near undetectable after 5 days of co-culture
      • Conversion to acetate via the Wood-Ljungdahl pathway.
  • Acetogens have a positive impact on the human body
    • Energy harvest
    • Acetate can be absorbed by the host for use as an energy source
  • Acetate produced via the Wood-Ljungdahl pathway
    • Account for up to 33% of acetate produced by fecal cultures
  • Acetogens may provide benefits to other bacterial groups - cross-feeding mutualism
    • Roseburia intestinalis and B. hydrogenotrophica when the pair were grown on xylan
      • R. intestinalis converted xylan to butyrate, releasing hydrogen for acetogenesis
      • Acetate produced by the acetogen - R. intestinalis resulting in higher butyrate production by the co-culture than the monoculture
  • www.ncbi.nlm.nih.gov/pmc/articles/PMC6546324/

Methanogens

  • Limited by low pH, even in the range found within the proximal colon
    • Can be as low as pH 5.5.
  • Limited by their inability to degrade sugars
    • Therefore obligate cross-feeders
    • Dependent upon the products of carbohydrate degraders for survival
  • www.ncbi.nlm.nih.gov/pmc/articles/PMC6546324/

Sulfate-reducing bacteria - SRB

  • Greater taxonomic diversity than the methanogens
  • Able to utilize a wider range of substrates for growth
  • Desulfovibrio genus
    • Dominant SRB clade in the colon
    • Able to reduce sulfate compounds to hydrogen sulfide (H2S)
    • Simultaneously oxidizing lactate to acetate
  • Desulfovibrio piger
    • Has an obligate requirement for sulfate in order to oxidize lactate
    • Was able to reduce sulfate effectively at pH 5.5 – substantially more acidic conditions than the neutral pH supportive of GIT methanogens
  • Other SRB species
    • Metabolize substrates such as the SCFAs acetate, butyrate and propionate, ethanol and pyruvate
    • Usually absent or found at low counts in the GIT

Sulfate may be derived in the GIT from

  • High-protein foods - animal products
  • Inorganic sulfate present in Brassica vegetables
  • Generated from the breakdown of endogenous sulfur-containing mucins

Kompetice o laktát

  • SRB are unable to degrade these structures
    • Rely on other members of the microbiota to release free sulfate during their metabolism of mucins
    • Cross-feeding actions of the SRB Desulfovibrio desulfuricans on free sulfate produced by Bacteroides fragilis during mucin breakdown
  • Sulfate-reduction pathway of SRB is dependent on
    • Availability of sulfate
      • Thus is often dependent on cross-feeding for this substrate
  • D. piger
    • Cross-feed on lactate produced by Bifidobacterium adolescentis
    • Compete for this substrate against the butyrate-producers
      • Eubacterium hallii
      • Anaerostipes caccae
    • Unaffected by the presence or absence of either or both of the butyrate producers
      • Due to more effective lactate scavenging by the SRB
O úroveň výše

Poslední aktualizace: 31. 7. 2022 2:11:12