9_Microbiota

Question 1

normal flora:

define

Answer 1

• symbiotes (bc they live in close association w/ the host)
• some relationships w/ the host are mutually beneficial and some are commensal (where the organisms benefit, but the host does not)
• If microbes stay confined to the GI tract, they are harmless and may even be beneficial

Question 2

how much of the normal flora is:

1. anaerobic
2. facultative

Answer 2

1. > 90% are anaerobic Gram negative bacteria
2. 10⁷ are facultative Gram negative bacteria; mostly bacilli

The rest of microbes are mix of Gram positive cocci, fungi, and viruses

Question 3

beneficial effects of the normal flora of the GI tract

Answer 3

• primes the immune system
• induces isohemagglutins by cross-reactions
• excludes pathogens
  
  • Abx tx that targets normal flora sensitizes to pathogens
  • Human can be sensitized to C. difficile
• produces vitamin B and vitamin K
• metabolizes bile salts for recycling
• metabolizes bilirubin

Question 4

what are the normal flora of the GI tract?

(categories and specific bacteria)

Answer 4

• Anaerobes
  
  • bacteriodes species are most numerous
• Facultative gram negative bacteria
  
  • E. coli
  • Klebsiella pneumoniae
  • Enterobacter species
  • Proteus species
  • Pseudomonas aeruginosa
  • Citrobacter species
  • Serratia species
• Gram positive cocci
  
  • Enterococcus, Staph aureus
• yeasts
  
  • Candida albicans

Question 5

microbiome vs. microbiota:

define

Answer 5

• microbiome: collective genome of the GI tract;
  
  • up to 40,000 bacterial species identified by 16S RNA
  • most of which are not culturable
  • about 100X as many microbial genes in the gut as human genomes
• microbiota: actual cultured microbes

Question 6

what are some diseases states of the microbiome?

Answer 6

• ulcerative colitis (UC)
• Crohn’s disease (CD)
• inflammatory bowel disease (IBD)

Question 7

How does the core gut microbiome in obese and lean twins compare?

(a study)

Answer 7

• compared monozygotic and dizygotic twin pairs;
• microbiome is shared among family members; but that each person’s gut microbial community varies
• obesity was assoc. w/ phylum-level changes in the microbiota, reduced bacterial diversity, and altered representation of bacterial genes and metabolic pathways
• Mice study: Recipient mice had body mass and metabolic characteristics of the donor of the fecal transplant

Question 8

probiotics:

define and examples

Answer 8

• Probiotics: are live bacteria and yeasts that are good for you, especially your digestive system
• In general have not been rigorously tested in trials
• Examples:
  
  • VSL#3, a mix of 8 bacteria, incl. L.
    acidophilus, L. casei, L. plantarum. L. bulgaricus,
    Bifidobacterium longum, B. breve, B. infantis and
    Streptococcus thermophilus has shown some efficacy in
    ulcerative colitis patients

Question 9

fecal transplant:

define,

Answer 9

• fecal transplant: (fecal bacteriotherapy) is the process of restoring the bacteria commonly found in the digestive tract with an infusion of feces (stool) from a donor
• How did the C. difficile patient differ prior to fecal transplant and after?
  
  • prior to transplant, patient did not have Bacteroides
  • after transplant, the pt DID have Bacteroides and started having normal bowel movements

Question 10

Kellogg’s findings and what effect did this have?

Answer 10

• Kellogg attributes “neurasthenia” or nervous exhaustion to eating of meat, which leads to growth of putrefying bacteria in the gut
• Effect
  
  • Advocates cereals and grains that have fiber
  • Invests in cold cereals
  • Advocates enemas to speed colonic transit and flush out putrefying toxins in a gut

Question 11

Colonic cleansing:

define

Answer 11

• popular technique to eliminate “toxins” in the GI tract
• NO evidence that they’re beneficial
• Side effects:
  
  • can cause ion imbalances
  • gut perforation
  • amoebic dysentery, if flush water is contaminated
  • adverse effects

Question 12

pathogenic effects of the normal flora in the GI tract?

Answer 12

• overgrowth of organisms from the large intestine –> small intestine –> malabsorption syndromes
  
  • malabsorption of fat, vitamin B12, folic acid, and carbohydrates
• cancer by production of nitrosamines
• escape from GI tract leading to pneumonia or UTI
• escape from gram negative bacteria from the GI tract leading to bacteremia, sepsis, endotoxic shock, and multiple organ failure
  
  • ruptured appendix, perforation of intestine by wounds or accidents

Question 13

CC: sepsis

Answer 13

life threatening organ dysfunction caused by a dysregulated host response to infection;

identified by change in SOFA score (sequential sepsis related organ failure assessment)

Question 14

CC: septic shock

Answer 14

subset of sepsis where the underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality

Question 15

How do infections and sepsis overlap?

Answer 15

• **bacteremia
• fungemia
• parasitemia
• viremia

Question 16

what are the non-septic causes of SIRS?

(systemic inflammatory response syndrome - SIRS)

Answer 16

• trauma
• burns
• injury
• ischemia

Question 17

how do the gram positive cell walls and the gram negative cell walls differ?

Answer 17

• Gram negative cells have the gram negative outer envelope;
  
  • the outer membrane contains LPS (lipopolysaccharide)

Question 18

what causes the endotoxic activity in gram negative bacteria?

Answer 18

• LPS (lipopolysaccharide) contains the endotoxic activity of Gram negative bacteria
• the TOXIC activity is in the lipid portion of the molecule

Question 19

What are the symptoms caused by endotoxins from different organisms?

Answer 19

they all lead to the same constellation of symptoms:

• fever, chills
• disseminated intravascular coagulation
• BP to fall (hypotonic shock)
• multiorgan failure
• death

Question 20

O antigens:

define

Answer 20

• repeating units of 3-5 sugars that give antigenic specificity to the organism
• highly variable from one species or serotype to another
• part of LPS (endotoxin)

Question 21

core antigens:

define

Answer 21

• repeating units of 3-6 polysaccharides that are somewhat conserved w/in a genus
• part of LPS (endotoxin)

Question 22

lipid A:

define

Answer 22

• multiple long chain fatty acids attached to a backbone of glucosamines; conserved w/in a genus
• part of LPS (endotoxin)

Question 23

what do you call the endotoxins of genera that are missing O antigens?

Answer 23

LOS: lipooligosaccharides

Ex. Neisseria

Question 24

How do Endotoxins and Exotoxins differ?

Answer 24

Question 25

how do almost all gram negative organisms have endotoxic activity, even with diff't structures?

Answer 25

* LIPOPOLYSACCHARIDES FROM ALMOST ALL GRAM NEGATIVE ORGANISMS HAVE ENDOTOXIC ACTIVITY. HOW CAN THIS OCCUR IF THEY ALL HAVE SLIGHTLY DIFFERENT STRUCTURES? WHAT IS THE RECEPTOR? * They have a new class of receptors called "Pattern recognition receptors" (PRRs) * these recognize PAMPs (pathogen-assoc. molecular patterns) * One class of PRRs is **toll-like receptors (TLRs)**

Question 26

which pattern recognition receptor recognizes LPS?

Answer 26

LPS is recognized by the Toll-like receptors?

Question 27

TLR -- Ligand -- Target microbes 1. TLR 1 2. TLR 2 3. TLR 3 4. TLR 4 5. TLR 5

Answer 27

1. **TLR 1** -- triacyl lipopeptides -- mycobacteria 2. **TLR 2 --** peptidoglycans, GPI-linked proteins, lipoproteins, zymosan -- gram-positive bacteria/trypansosomes/mycobacteria/yeasts and other fungi 3. **TLR 3** -- lipoteichoic acid (dsRNA) -- viruses 4. **TLR 4** -- LPS, F-protein -- gram-negative bacteria, respiratory syncytial virus (RSV) 5. **TLR 5** -- flagellin -- bacteria

Question 28

what is the pathophysiology of Septic shock and Multiple organ failure?

Answer 28

* release of massive amounts of TNF-alpha and other proinflammatory cytokines --\> * leads to septic shock and multiple organ failure * induction of nitric oxide leads to fall in blood pressure and circulatory collapse

Question 29

cytokine and it's respective functions: * IL-1 * IL-12 * TNF-alpha * IL-6 * IL-8

Answer 29

* IL-1 -- fever, activated endothelial cells * IL-12 -- activates NK cells * TNF-alpha -- causes tissue damage and mediates septic shock * IL-6 -- induces acute phase proteins in the liver * IL-8 -- is chemotactic for PMNs (polymorphonuclear leukocytes)

Question 30

describe the ligand and effector of **TLR-4**

Answer 30

TLR 4 responds to LPS, F-protein Targets gram-negative bacteria and respiratory syncytial virus (RSV)

Question 31

podiatry and septic shock? when will you see it?

Answer 31

* bacteria in wounds, bed sores, and infected toe nails * esp in elderly in care facilities --\> can move into blood stream * gram negative organisms in the blood stream * can give a similar syndrome of septic shock * even though they are not seeding from the GI tract * gram positive organisms infect skin * can also cause sepsis by triggering TLR2, although peptidoglycan is much less potent than LPS