BACTERIAL INFECTIONS OF THE GIT

(Micro made easy pp54) Gram - ve

Escherichia coli: There are 5 pathotypes: EPEC, ETEC, EIEC, EHEC, EDEC, DAEC (diffusely adherent). All types have flagellum.

• ETEC: This organism attaches itself to the epithelial cells. It then releases two toxins: HL & HS toxin. These bind to the epithelial cells and block reabsorption of Na+ / Cl- and promote secretion of HCO3- / Cl-. Therefore H2O follows the osmotic pull gradient, and you lose lots of water ≫ watery diarrhoea≫ travellers diarrhoea.

• EIEC: Bacteria has a plasmid (i.e.: extrachromosomal DNA), that encodes a virulence factor≫ allows invasion of epithelial cells. Also produces Shiga-like toxin. Both of these illicit a cell mediated immune response ≫ causing fever, bloody diarrhoea.

• EHEC (1-10 organisms): This organism attaches itself to the epithelial cells, and releases the Shiga-like toxin. This toxin inhibits protein synthesis ≫ killing the epithelial cells. It causes abdominal pain, bloody diarrhoea ≫ haemorrhagic colitis. HUS (haemolytic uraemic syndrome) occurs in patients infected with O157 serotype of EHEC.

• EPEC: This organism attaches to the mucosa and damages the brush border of intestinal epithelium ≫ impairs function. Also associated with HUS.

• EAEC: travellers diarrhoea.

Salmonella: There are three main clinical types: Salmonella typhi/paratyphi, Salmonella choleraesuis, Salmonella enteritidis. All of these is carried by animals, except typhi/paratyphi.

• Salmonella typhi/paratyphi (1-10² organisms): This organism causes typhoid fever (enteric fever). Like Shigella & EIEC, it invades the epithelium and enters the lymphatics ≫ nodes. During this time it is phagocytosed by macrophages ≫ but it still survives. It causes fever, headaches, abdominal pain, splenomegaly (spreads to here), rashes on belly (“rose spots”), diarrhoea.

• Salmonella enteritidis: Out of all salmonella infections, this is most common. It causes classic diarrhoea syndrome symptoms. Diarrhoea can be watery (i.e.: cholera like toxin) or mucousy/specks of blood – 5% (i.e.: ileal inflammation). Treated by fluid / electrolyte replacement, antibiotics not indicated.

Shigella (dysenteriae, flexneri, boydii, sonnei) (10² organisms): Shigella species is non motile, unlike E. coli and Vibrio Cholera. Also Shigella does not ferment lactose or produce H2S, while E coli (lactose fermenter) & Salmonella (H2S producer). It is transmitted via faecally contaminated water + hand-hand contact. Shigella produces shiga toxin which inhibits protein synthesis and kills epithelial cell. Immune cells converge and cause reaction. Destroyed epithelium is not able to absorb H2O + electrolytes ≫ bloody diarrhoea, fever, abdominal discomfort. Treatment: ciprofloxacin, ampicillin, quinolones.

Yersinia enterocolitica & Y. pseudotuberculosis: Transmission is by ingestion of contaminated milk, water, & foods. Children < lang="en-AU">≫enteritis, 5-15 ≫ mesenteric adenitis, 10-20  terminal ileitis. Adults ≫ rashes/arthritis.

Campylobacter jejuni (coli, laridis, foetus) (10⁸): What are the three most common causes of diarrhea? Campylobacter, ETEC, Rotavirus. This is a zoonotic disease (poultry + wild animals). Transmission is via faecally contaminated water, food + unpasterurised milk. Like Salmonella typhi, the organism penetrates the epithelium and enters the lymphatics to spread (also secretes LT). Symptoms: fever, nausea, vomiting, bloody diarrhea, abdominal discomfort.

Vibrio cholerae: Deadly disease. Curved shaped gram negative rod (as most enterics are!!) with flagellum. Transmission is via faecally contaminated water. Bacteria attaches to epithelial cells, releases the cholera toxin (A + B subunit, where B helps A get in and activate G protein reactions ≫ increases intracellular cAMP≫ causes secretion of Na+/Cl-  lose water in HUGE amounts!!). Cause of death = dehydration. Treatment = fluid + electrolyte balance + doxycyclin.

BACTERIAL INFECTIONS OF THE GIT (Micro made easy 45) Gram +ve

Listeria monocytogenes: This is a gram positive non-spore forming rod, with endotoxin. This is mainly the culprit of meningitis in neonates and the immunocompromised. It can causes gastrointestinal upset, is transmitted by contaminated foods (milk, water etc).

Category: Microbiology Notes