Intestinal Microbiology Flashcards
what is the microbiome?
Complex, interactive, community and ecosystem containing over 1,000 bacterial species
Anaerobes outnumber
facultative anaerobes
Microbiota is sparse in the
stomach and upper intestine (duodenum, jejunum and upper ileum)
microbiota is extensive in
the lower bowel
Bacteria occur in both the
lumen and attached to the mucosa but do not normally penetrate the bowel wall
describe normal microbiota
symbiotic, mutualistic relationship
describe pathogenic microbiota
opportunistic
Normal Microbiota in the blood stream or peritoneal cavity will become
pathogenic
Colonisation of the upper digestive tract is an abnormal event and characteristic of
certain pathogens, for example:
Vibrio cholerae (cholera)
escherichia coli (gastroenteritis)
helicobacter pylori (stomach ulcer)
the appendix is known as…
… the seed house for th ehuman gut microbiome
gastric aci dkills most…
… organisms that are swallowed
gastric acid results in
high incidience of bacterial colonisation / bacterial diarrhoeal disease
bile has
antibacterial properties
how does peristalsis help control normal microbiome balance?
- Forward motility suppresses Microbiota of upper bowel
describe the microbiome
- Produce their own anti-bacterial substances
- Bacteriocins and short chain fatty acids
- These stabilise normal populations and prevent implantation of pathogens
the microbiome is extremely diverse and capable of using virtually any compound in the intestinal lumen as a
substrate
Endogenous substances
that undergo
enterohepatic circulation:
- Bilirubin
- Bile acids
- Cholesterol
- Oestrogens
Intestinal bacteria metabolise bile acids rendering
them
more easily absorbed by the intestinal mucosa -
Contributes to enterohepatic circulation
Many drugs that are excreted by the liver (digitalis,
morphine, rifampin, chloramphenicol) and antibiotics
block
enterohepatic circulation by suppressing intestinal
microbiota.
Enzymes produced by intestinal bacteria produce some important vitamins:
Vitamin K
Vitamin A
Thiamine
Folic Acid
BIotin
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Intestinal microbiome relatively stable over time and discourages
infections by exogenous pathogens and prevents overgrowtho of potentially pathogenic members,
antibiotics can upset
microbiome balance and may leave the intestine open to infection eg: salmonella
Healthy individuals are often resistant to
salmonella and wuite a large incolum is required to initiate infection.
antibiotics sppress
intestinal microbiota -> individual becomes more susceptible.
Clostridium difficile: Causes
GI infection due to
bacterial overgrowth and results in severe
inflammation of the colon
how is C. difficile GI infection initiated?
Initiated by suppression of normal microbiome with antibiotics.
what is Peritonitis?
breach of the mucosal wall by trauma allows entry of bacteria into a
normally sterile area.
Poor circulation, low oxygen supplies and dead tissue favour the growth of
anaerobic bacteria which results in peritoneal abscesses
Several enterotoxin-producing bacteria cause diarrhoeal disease
- Vibrio cholerae
- E. coli
- Shigella
- Staphyloccoccus aureus
- Clostridium perfringens
Diarrhoea induced by pathogens →
guts react to toxins and contract.
Diarrhoea induced by pathogens causes
expulsion defence mechanism and diarrhoea
Diarrhoea Treatment
- Opioid-receptor agonist drugs
- Diphenoxylate / Loperamide / Morphine
- µ-opioid receptor agonist inhibits the myenteric plexus
(motor activity) of the large intestine - Loperamide: Low CNS absorption through BBB
- Morphine: high absorption
- Decrease muscle tone of the intestines > reduce GI activity
fluid from the body is normally
pumped into the intestinal lumen during digestion
Fluid from the body is normally pumped into the intestinal lumen
during digestion.
- this fluid is typiclly
isotonic with blood because it contains a high
concentration of Na+.
how much Na+ will a healthy individual secrete per day
A healthy individual will secrete 20-30 grams of Na+ per day via
intestinal secretions.
A healthy individual will secrete 20-30 grams of Na+ per day via
intestinal secretions.
Nealy all of htis is
reabsorbed by the intestine, helping to maintain constant Na+ levels in the body (homeostasis)
Heavy continuous diarrhoea can become
a potentially life threatening condition within hours.
Liquid secreted into the intestinal lumen passes through the
gut so quickly that little Na+ is reabsorbed
- Heavy continuous diarrhoea can become a potentially life
threatening condition within hours. - Liquid secreted into the intestinal lumen passes through the gut
so quickly that little Na+ is reabsorbed - Leading to…
… dangerously low sodium levels in the body (severe hyponatremia).
what are the 3 main characteristics of diarrhoeal diseases?
1) Intestinal fluid loss, related to the action of an enterotoxin on the small bowel epithelial
cells.
2) Organism does not invade the mucosal surface – colonises the upper small bowel
adhering to the epithelial cells and producing the enterotoxin.
3) Faecal effluent (originating from the upper intestine, where the toxin is most active) is
watery and often voluminous – clinical dehydration
what is cholera causes by?
Caused by Vibrio cholerae usually ingested
in contaminated water
cholera stool volume?
Stool volume can exceed 1 L/h with daily faecal outputs of 15-20 L if the patient is kept hydrated
30+
