E3. Helicobacter pylori Flashcards
Normal bacteria present in?
-Tongue/mouth
-Saliva: millions of bacteria per ml
-Oesophagus/stomach: very few bacteria
Bacteria present in lower digestive tract?
-Lower part small intestine/colon: trillions of bacteria
-Bacteria constitute 40% of dry weight of faeces
Bacteria which causes nausea, vomiting and diarrhoea?
Campylobacter jejuni
Salmonella spp
Shigella spp
Escherichia coli
Vibrio cholerae and more
-Short term survival, but unable to colonise
Bacteria which causes gastric ulceration?
Helicobacter pylori
Long term survival and able to colonise mucus lining the stomach
Describe helicobacter pylori infections
-Infection very common, usually during childhood
-Infects lower part of the stomach (antrum)
-Stomach ulcers in some (15%)
Increased risk of stomach cancer
-Symptoms usually not present until adulthood
-Not everyone with H. pylori develops symptoms
Asymptomatic infections are not well understood:
-Individual characteristics (immune system)
-Varying strains of H. pylori
-Other unknown environmental factors
ONE NOTE
Requirements for the colonisation of the stomach from Helicobacter pylori?
1)Acid neutralising system
Urease enzyme, transporter proteins
2)Adhesion molecules
Present on outer membrane; bind sugar molecules on surface of stomach
3)Movement
Flagella
4)Degradation of mucus
Enzymes: lipases, proteases
consequences of helicobacter pylori colonising the stomach?
-The mucus layer is damaged
-Epithelial cells are no longer protected against gastric acid
Describe the acid neutralising activity of Helicobacter pylori
ONE NOTE
Describe the urease enzyme
Two amino acid chains:
a-chain: 238 amino acids
B-chain: 569 amino acids
Describe the proton gated urea channel
-Single amino acid chain of 195 amino acids
-Ring-like structure with pores to permit urea transport
‘Proton-gated’ (pH sensitive):
pH <5.0 channel fully open
pH >7.0 channel closed
Non-invasive diagnostic tests for H.Pylori?
-Breath test
-Stool antigen test
-Blood test
invasive diagnostic tests for H.Pylori?
-Gastroscopy and take biopsy for culture
-Advantage: sensitivity testing
- Patients with reduced antibiotic choice (hypersensitivity, previous use of antibiotics)
- Patients who received eradication therapy, but remain Helicobacter positive
Sensitivity of a diagnostic test?
The ability of a test to correctly identify those with the disease
Specificity of a diagnostic test?
The ability of the test to correctly identify those without the disease
Describe urea breath test
-Detection based on urease enzyme activity
-Most commonly used test
-Based on detection of heavy isotopes
13C label: non-radioactive
-Measured using mass spectrometry or isotope-selective infrared spectroscopy (for information only)
ONE NOTE
What is the purpose of each drink ingredient in the urea breath test?
-Citric acid (low pH):
Ensure proton-gated urea channel is open
-Sugar (mannitol; high calorie):
Ensure parietal cell is actively secreting
-Labelled urea:
Substrate for urease enzyme
-Flavour compounds:
Make the test agreeable for the patient
Describe stool antigen test
-Antibodies are key components of the immune system
-Able to bind antigen
-Used in the test to detect antigen
ONE NOTE
Describe blood test
-Laboratory based antibody detection
-Quantitative
-ELISA (Enzyme-linked Immuno-Sorbent Assay)
-Multiple tests can be carried out in parallel
ONE NOTE
How to calculate pH of an acid?
pH = -log10[H3O+]
ONE NOTE
How to calculate [H3O+]?
[H3O+] = 10-pH
ONE NOTE
How to calculate pH of a solution of a strong base?
ONE NOTE
How to calculate the pH of a solution containing a mixture of a strong
acid and strong base in the case of ‘incomplete neutralisation’?
- Work out the excess amount (in moles) of H3O+ (or HO-) remaining after the addition
- Calculate the [H3O+] (or [HO-]) remaining after addition (in M). Take care to consider the
total volume of the new solution - Calculate pH
EXAMPLE ON ONE NOTE
How to calculate the pH of solutions containing weak acids and/or
weak bases?
1) Calculating the pH of a solution of a weak acid
2) Calculating the pH of a solution of a weak base
3) Calculating the pH of a solution containing a mixture of a strong acid and weak base or
weak acid and strong base
ONE NOTE
The Henderson-Hasselbalch equation?
ONE NOTE
