Microbiology Of The Gut Flashcards
What are the types of GI infections?
Non-inflammatory
Inflammatory
Penetrating
Which pathogen uses the GI tract as a mode of entry but generates no GI symptoms?
Poliovirus which is transmitted by aerosols OR foecal contamination of hands and the mouth. It replicas in the oropharyngeal mucosa and lower gastrointestinal mucosa to invade the bloodstream and cause degradation of motor neurones.
There are three serotypes; PV1, PV2 and PV3 which are present in the saliva and faeces of infected people.
What causes non-inflammatory GI infection?
Infection occurs in the proximal small bowel, by the action of entero-toxins or mucosal adherence from pathogens.
E.g Vibrio cholerae, E.Coli and Baccilus cereus.
What causes inflammation of GI tract?
Colon is subject to mucosal invasion or cytotoxic damage from pathogens. These include Shigella, Campylobacter jejuni, Salmonella and E.Coli.
What causes penetration of GI tract?
Distal small bowel is the target by pathogens for phagocytosis. These pathogens are salmonella, Yersinia and Listeria monocytogenes.
What is gastroenteritis?
Acute infection that causes inflammation of the GI tract, which causes abdominal pain, diarrhoea and vomiting. Antibiotics rarely are useful and there is typically a travel history and can cause post-infection syndromes.
What is post-infection syndromes for gastroenteritis?
Can lead to damage to the bowels and create lactose intolerance.
What are enterotoxins?
Toxin produced by bacteria which acts on the intestines. It binds chronically to the Gs protein coupled receptor to increase cAMP levels for high Cl- efflux that leads to loss of water in the lumen and watery diarrhoea.
What are cytotoxins?
Toxin produced by bacteria which causes cell damage for replication.
What are exotoxins?
Produced by gram ve+ bacteria which act as superantigens to cause dysregulated immune response and damage cells.
What are endotoxins?
Released from LPS in gram ve- bacteria death which elicit a strong immune response of sepsis and are heat stable.
What are the immune defences in the gut?
Low gastric pH
Mucus barrier containing lysosomes and IgA
Peristalsis to move contents of gut very fast
Bile salts and acids which target the fat in membranes to cause emulsification.
Presence of gut-associated lymphoid tissue called Peyer’s patches containing B and T cells
What are bile acids?
Synthesised by the liver and secreted into the bile. They promote absorption of fat in the small intestine.
What are bile salts?
Bile salts are bile acids that have been conjugated with glycine and taurine. Bile salts are important for fat emuslification.
What is the composition of the gut mucosa?
Epithelia lined with microvilli to promote reabsorption, and contain crypts filled with stem cells. The epithelia have a mucosal layer containing lysosomes and IgA. Below this is the lamina propia, dense connective tissue containing activated immune cells like lymphocytes.
Where do the Peyer’s patches drain?
They are lymphoid associated tissue which remove pathogens into the lymphatic circulation via the mesenteric lymph nodes.
What is the composition of Peyer’s patches?
The luminal side is lined with follicle associated epithelial cells containing M cells called micro fold cells which take up antigens to transport to the follicle of Peyer’s patches. The follicle is where B cells reside with T cells and dendritic cells in the surrounding area.
How do naive B and T cells enter the Peyer’s patches?
Peyer’s patches release chemokines in response to pathogens in the gut which attracts lymphocytes which are taken up by endothelial venules.
How are pathogens taken up from the gut contents?
The antigen is transported across the epithelial lumen to the peyer’s patches by M cells via transcytosis. This is then delivered to dendritic cells to present on MHC receptors for activation of lymphocytes. B cells will produce IgA antibodies to be delivered to the laminate propia for mucosal protection of the gut
How does the gut maintain colonisation resistance?
Commensal bacteria of the gut produce toxins called bacteriocins to inhibit the growth of pathogenic bacterial strains.
End products of food metabolism are toxic to pathogens.
There is stimulation of local immune system cells.
Where are the majority of the GI flora located?
In the colon, which contains mainly anaerobic bacteria. These include Lactobacillus, bifidobacteria, enterococcus and enterobacteria.
What is the apppendix?
Open-ended tube connected to the caecum which contains lymphoid tissue.
Its function is unknown but can become a target for infection by cholera or Clostridium difficile that leads to necrosis and bursting of faeces into abdominal cavity.
What is the micro biome?
Sum of all the species in the bowels, which composes majority of the stools. The bacteria in the micro biome are synergistic, and release energy such as sugars, nutrients and outcompete pathogens. When they are found extra-intestinally, it causes peritonitis and urinary tract infections.
Which nutrients does the micro biome release?
Iron, calcium and amino acids
What is clostridium dificile?
Gram positive bacilli bacteria which forms spores, and is part of the commensal bacteria of the microbiome. It can become pathogenic with the use of antibiotics, proton pump inhibitors and lead to complications such as pseudomembranous colitis and toxic megacolon.
What is pseduomembranous colitis?
Inflammation of the colon that leads to yellow cobblestone plaque formation, by infection with C.dificile.
Which group is at risk of C.dificile infection?
Elderly and those with a weakened immune system.
What are the common causative agents of C.difficle infection?
Antibiotics:
Clindamycin
Cephalosporin
Ciprofloxacin
Co-amoxiclav
How is C.difficile infection treated?
Foecal-oral transplant
Isolate patient until 48hrs after last diarrhoea, but there is a high recurrence rate
Hand washing and disinfection of patient contaminants is important
Use of vancomycin, findamycin and metronidazole.
How is clostridium difficle diagnosed?
Presence of toxin glutamate dehydrogenase.
Stool culture is not diagnostic.
