Microbiota Flashcards
What functions do commensal bacteria carry out?
- development of the immune system
- provide energy for metabolizing dietary polysaccharides
- provide vitamins
- protect from pathogenic bacteria
Characterize the location and composition of commensal bacteria in the body.
- various locations; mostly mucosal (skin, GI, genitals, mouth)
- various compositions: differs from location to location
Describe the role of commensals during a C. diff infection.
- Typically you have a layer of commensals lining the GI tract. After administration of antibiotics, this protective layer is diminished and gives an edge to pathogenic bacteria
- c. Diff is able to infect epithelial cells of the GI tract and cause apoptosis
- The damaged epithelial lining is further damaged by neutrophils and RBCs entering the gut.
Describe the role of commensals in traveler’s diarrhea.
Mice that are provided commensal b. subtilis are protected from E. coli
Describe the role of commensals in balancing immune response.
- some bacteria initiate a pro-inflammatory cascade; other bacteria initiate an anti-inflammatory cascade
- Typically, Th1 and Th17 is initiated in response to pathogenic bacteria => intestinal inflammation
- Tregs keep this inflammation in check
- dysbiosis can tip the balance in favor of Th17 => inflammation => damage
List some pro-inflammatory bacteria.
- SFB => Th17
- S. typhimumum => Th1
List some anti-inflammatory bacteria.
- B. Fragilis => Tregs
Describe the role of commensal bacteria in IBD.
- dysbiosis has been linked to IBD
- if you transfer microbiota of someone with IBD into a normal individual, the healthy individual will develop IBD => hence, microbiota is key
- Tx: B. fragilis (anti-inflammatory)
Describe the hygiene hypothesis.
Prevention of exposure in children can lead to increased allergy, asthma, etc. prevalence
- the larger the family, the more pathogens encountered => less likely
- more exposure to animals, plants, getting dirty => less likely
- more exposure to other children early on (day care) => less likely
- more infections in early childhood => less likely
Describe the mechanism by which commensal bacteria protect against allergy.
- Typically, bacteria and viruses initiate a Th1 response via IL2 and IFNg
- Th1 downregulates Th2 response (Th2 is responsible for IgE production => more allergies)
- if you have decreased exposure to bacteria and viruses => decreased Th1 responses => upregulation of Th2 => more IgE => more allergy
Describe the role of commensals in autoimmunity.
- microbiota can protect against autoimmunity symptoms b/c they upregulate Tregs
Describe the role of commensals in metabolic disorder.
- lack of TLR5 (which recognizes bacteria)
- leads to obesity, type 2 diabetes, and cardiovascular disease (exacerbated by high fat diet)
- dysbiosis
- microbiota transplant from obese mice => antibiotic-treated mice ====> normal mice become obese
- microbiota transplant from lean mice => obese mice =====> obese mice become lean
- microbiota transplant from lean human to mice and obese human to mice ==> lean mice, obese mice
How does a high fat diet contribute to dysbiosis, and subsequently obesity?
- high fat causes innate lymphoid cells to secrete IL-22
- IL-22 induces expression of anti-microbial peptide ====> diminishes protective microbiota
List causes of dysbiosis.
- antibiotics (lead to EAE, Type 1 and Type 2 DM, allergy, asthma)
- diet (high fat => IL22)
- hygiene hypothesis
- vaginal vs cesarean delivery
How does vaginal or cesarean delivery affect the baby?
- vaginal babies had microbiota similar to mom’s vagina
- C-section babies had microbiota similar to mom’s skin
- composition varies in the C-section babies => more likely to develop allergies, etc.
