Microbiology Of The Gut Flashcards
What are the mechanisms/categories of GI infection (3)?
Non inflammatory
Invasive/inflammatory
Penetrating
Give an example of a virus that uses the GI tract for entry point but with no/little GI symptoms?
Polio virus
What is the mechanism of non-inflammatory GI infections?
Enterotoxins (may be pre-formed in food that’s ingested), mucosal adherence
What is the location of non-inflammatory GI infections
Proximal small bowel
Give examples of non-inflammatory GI infections?
Vibro cholerae - Cholera disease produced by cholera toxin
Bacillus cereus - emetic toxin causes vomiting, heat stable, associated with rice, long-acting toxin also produced which causes nausea and diarrhoea
Enterotoxigenic E.coli- toxin produced is similar to cholera toxin
What is the mechanism of inflammatory GI infections?
Invasion of mucosa production of cytotoxinsq
What is the location of inflammatory GI infections?
Colon
Give examples of inflammatory GI infections
Shigella sp. - produces shigella toxin (most potent toxin known), invades GI epithelium and spreads laterally along epithelial layer (local invasion of tissue)
Salmonella sp. - invades local epithelial GI cells, which causes nausea, vomiting and diarrhoea
Campylobacter jejuni - can mimic acute appendicitis, inflammatory adenitis and can be mistaken for Crohn’s disease
Enterohaemorrhagic/Enteroinvasive E.coli
What is the mechanism of penetrating GI infections
Induced phagocytosis, invades cells of the immune system and disseminate beyond the gut
What is the location of GI infections?
Distal small colon
Give examples of penetrating GI infections
Salmonella typhi - symptoms start 6- 30days post contact, slow onset of high grade fever, generalised weakness, cramps, disseminates into bone marrow and tissue macrophages
Yersinia enterocolitica - gastroenteritis, but can invade immune system as well
Listeria monocytogenes - disease of extremes of age (very young, old, immunocompromised), invades cells of immune system, gastroenteritis, can cause meningitis if spreads
What are the sensory host defences against GI infections?
Smell taste
What are the behavioural host defences against GI infections?
Pooing in the toilet, away from food - sewer system keeps sewage separate from drinking water
Washing hands after going to toilet
What are the physiological host defences against GI infection?
Gastric pH - 1.5-3.5pH, achieved mostly by HCl
Bile salts and acids - in proximal small bowel, attacks bugs which get through
gastric acid
Peristalsis - maintains movement to prevent time for microorganisms to settle on
epithelium and start an infectious process
Mucus - gut epithelia produces mucus which is a physical barrier and is full of
antimicrobials (e.g. lysozyme) - mucus can also be upregulated by signalling molecules if there is an infection to create more of a barrier to prevent more tissue damage
What are the immune system defences against GI infection?
Humoral (antibody-mediated) immunity with secretory IgA - binds to bacteria in gut
preventing them from accessing the epithelial cells (immune exclusion)
Cell-mediated immunity - involves patrolling macrophages and cell signalling
processes
GALT (gut associated lymphoid tissue) - acts as a focus for lymphocytes and
immune cells, aiding in recruitment if there is infection
What are the normal gut flora of the GI tract defences against GI infection?
Colonization resistance - occupies space, produces antibiotic-like substances (bacteriocins), end products of metabolism may be toxic
Stimulate local immune system
What is the function of microbiome?
Synergistic
Synthetic – forms folate, biotin, vitamin K, vitamin B
Promotes release of nutrients from foods – Fe2+, Ca2+, amino acids
Removes toxins from the breakdown of metabolism – alkaloyds, hydrogen,
heterocyclic amines from cooking
Out competes pathogens – colonisation resistance, prevents pathogen
establishment
Releases energy from carbohydrates by breaking them into sugarsk
What infection can GI regional flora cause if it gets into the rest of the body
Peritonitis
Urinary tract infections
What is the appendix?
What surround the appendix?
What are the benefits of having an appendix?
Vestigial remnant, but new research shows the appendix
The appendix is surrounded by lots of lymphoid tissue MALT (mucosal associated lymphoid tissue) which aids immune response to gut infection
The appendix stores a copy of your gut flora, so following an infection (e.g. cholera, C. difficile) where the diarrhoea flushes out the majority of your gut flora, the store can repopulate the gut with the healthy gut flora
Hence, patients who lack an appendix are much more prone to recurrences of C. difficile infection because it takes much longer for them to repopulate their gut flora
What are the symptoms of bacteria overgrowth
Diarrhoea Bloating Abdominal pain Flatulence Steatorrhoea – fatty stools o Weight loss
What diseases can occur due to bacterial overgrowth?
Fe deficiency – microcytic anaemia B12/folate deficiency – macrocytic anaemia Ca2+ deficiency – tetany Vitamin A deficiency – visual acuity Selenium – dermatitis Protein – weight loss, cachexia Fats – haemorrhagic stroke
How is a diagnosis of bacterial overgrowth occur?
Hydrogen breath test
Increase in total flora (1010 organisms/ml diagnostic)
What is the treatment of bacterial overgrowth?
Treat underlying condition – e.g. due to PPIs, needs to be reduced
Rifaximin
What is bacterial overgrowth syndrome?
Malabsorption (Steatorrhea, Diarrhoea) Deficiency of fat-soluble vitamins Macrocytic anaemia Diagnosis o >105 bacteria/ml in a proximal small bowel aspirate o 14C-D-xylose breath test • Management o Correct underlying condition o Nutritional supplements o Suppressive antimicrobial therapy
