SPECTRUM OF CLINICAL FEATURES / SYNDROMES (Lecture notes, Micro made easy, Chapter 9 – The enterics) – should know the different syndromes

• Non-inflammatory watery diarrhoea: This is caused by production of enterotoxins. Species that cause this include: ETEC (LT & ST inhibit Na+ Cl- reabsorption, loss of water follows), V. cholera (cholera toxin≫A + B subunit, B unit allows entry of A subunit ≫A subunit increases intracellular cAMP  drives Na+/Cl- out≫H₂O lost by osmotic pull).
• Inflammatory, dysentery: invade the epithelium and release toxins that causes cellular injury. Species that cause this include: EHEC (invade the epithelium ≫
• secrete Shiga-like toxin≫inhibit protein synthesis≫epithelial cells die), Shigella spp (same as EHEC), EIEC (same as EHEC).
• Hospital-acquired (antibiotic mediated) diarrhoea: Pseudomembranous colitis: This disease is caused by the exotoxins A+B produced by C. difficile. After dose of antibiotic, gut bacteria is altered≫C.difficle flourish≫release exotoxins that inhibit RhO protein synthesis in epithelial cell ≫disrupts actin filaments≫cells shrink ≫ and cell.
• Mucosal translocation, intra & submucosal proliferation: This type of diarrhoea is caused by species penetrate the mucosa and submucosa to spread via the lymphatics and blood. Species include: Salmonella spp, Campylobacter spp, Yersinia enterocolitica.
• Travellers diarrhoea: Name given to diarrhoea acquired by travellers due to ingestion of faecally contaminated food. Species that cause this include: E.coli, rotaviruses, Entamoeba histolytica (cysts present in faeces  eaten by others infecting them, also sometimes trophozoite form invades the GI epithelium causing erosion≫diarrhoea). Giardia Lamblia (trophozoites bind to epithelial cells  intestines cannot absorb fat ≫fat passes ≫fatty stools), Crptosporidium.
• Food-poisoning: outbreaks of diarrhoeal illness. Caused from a single point from which the illness spreads.
• Enteric fevers: These fevers are caused by organisms that invade the epithelium and enter submucosa ≫lymphatics. During this process they are ingested by macrophages, but they manage to survive. Examples are: Salmonella typhi, paratyphi A&B.
• Gastritis/duodenitis: Caused by helicobacter pylori.

PATHOGENESIS (Lecture notes)

Microbial factors

The pathogenesis of all types of diarrhoea requires the following microbial factors:

0) ability to survive the environment

1) ability to adhere to mucosa,

2) ability to penetrate the mucosa,

3) ability to produce enterotoxins/cytotoxins,

4) ability to multiply within host tissue.

Review the pathogenic mechanisms outlines above for each organism.

Host factors

The predisposing host factors to diarrhoeal illness stems from microbial factors:

1) decreased gastric acidity,

2) poor intestinal motility

3) disturbed normal flora,

4) decreased antibodies,

5) age,

Category: Microbiology Notes