M7: Bacteria affecting GIT Flashcards
1. Give a simple account of the composition of normal gut flora 2. List the main types of GIT infections, including food poisoning, diarrhoea, enteric fever and cholera 3. Summarise the modes of transmission of such infections and the principle methods avaliable for their control 4. Outline the main features and pathogenic mechanisms of common GIT bacteria including Escherichia, Salmonella, Shigella, Vibrio, Campylobacter, Klebsiella, Proteus, Pseudomonas
List ways in which the GIT limits exposure of the host immune system to the microbiota
- Via epithelial and mucus layer
- Biochemically via enzymes and antimicrobial proteins
- Immunologically via IgA and epithelia-associated immune cells
What is the normal gut flora function
To maintain gut homeostasis by
- strengthening the gut integrity
- shaping the intestinal epithelium
- harvesting energy
- protecting against pathogens
- regulating host immunity
Bacteria affecting stomach and the stomach environment
Low pH, bile, inhibitory usually sterile environment
H. pylori can resist - causes gastritis
Small intestine commensal flora
Jejunun - Enterococci, lactobacilli
Ileum - Enterobacteriaceae, Bacteroides fragilis (gram -ve anaerobes)
Large intestine commensal flora
Strict anaerobes (obligate)
Why is the normal GI flora beneficial
Because it provides competition against potentially pathogenic species
Attenuates mucosal immune response to pathogen so it controls inflammation
It enhances integrity of the epithelial barrier by provided nutrients for colonic epithelium
Maintains the gut mucosa and metabolism of toxic compounds
Produces folate and vitamin K from dietary precursors
Produces luminal IgA
What causes diarrhoeal disease
It is a major cause of illness in developing countries and occurs due to socio-economic factors such as
- lack of clean water
- sewage disposal
- food quility/balance
What are the two main mechanisms of diarrhoeal disease
- Invasive = bacterial invasion of tissues
2. Exotoxin = secretion in food of live bacteria
Bacteria involed in invasive diarrhoeal disease and what are the symptoms
Salmonella enteritis
Shigella dysenteriae - bacillary dysentery
Cramps in abdomen, pus and blood in stools
What is escherichia
Gram -ve rod, lactose fermenter
E. coli is the most common species
How does escherichia adhere to host cells
Via fimbriae on the cell surface and pili
What can E. coli cause
- GI infections
- UTIs
- Septic infections (wounds, abscesses)
- Neonatal meningitis
What protects E. coli from the host immune response
O = somatic antigens K = capsular antigens
Protect from complement activation and phagocytosis
What are the features of ENTEROPATHOGENIC E. coli
- Attachment and effacing lesions of intestine
- Acute enteritis of infants
- Tropical countries
- High mortality
- Non-invasive
What are the features of ENTEROTOXIGENIC E. coli
- Adhere to epithelium of small intestive
- Toxin mediated causing fluid loss
- Brief illness: vomiting, abdominal crapms, loose stools
- Acute enteritis = traverlers diarrhoea
What are the fetures of ENTERO-INVASICE E. coli
- Causes dysentery-like disease
- Invasive with bacteria entering epithelial cells of large intestine and multiplying here
What are the features of VERO CYTOTOXIGENIC E. coli
- Infection can lead to renal failure in severe cases
- Toxins produce VT1/VT2
- Severe outbreaks in paediatric and geriatric populations
- Haemorrhagic colitis (bloody diarrhoea)
Outline virulence mechanisms of E. coli
EPEC = adherence to epithelium via cytoskeletal rearrangement (calcium and electrolyte loss)
ETEC = toxin causing adenylate cyclase ribosylation and cAMP accumilation - leads to fluid secreteion
EIEC = epithelial cell invasion, destruction and spread
VTEC = Vero-toxin: inhibits ribosomal RNA and so stops protein synthesis
What is salmonella
Gram -ve bacilli, inhabit animal intestines, non-lactose fermeters
O (somatic) and H (flagellar) antiges
Outline pathogenesis of salmonella
Bacteria attach to epithelium of ileal mucosa
Invade and multiply in tissues
Salmonella gatro-enteritis symptoms
Cramps, diarrhoea, fever, vomiting, severe dehydration, renal failure
Where is the salmonella bacteria found
Poorly butchered meats
Eggs
Animals and human carriers
What is shigella
Gram -ve rods, non lactose fermeting - S. dysenteriae - S. flexneri - S. boydi These cause bacillary dysentery and frequent passage of bloody mucopurulent stools
How is shigella spread
Faecal-orally
Due to poor hygine
