Lecture 21 - Respiratory Tract Infections 2 Flashcards
(31 cards)
What are some of the things have we learnt from Pneumococcus?
- Gram stain
- opsonisation
- bacterial serotypes
- polysaccharide antigens (capsule)
- role of DNA
- protein virulence determinants
- vaccination
What are the antibodies to pneumococcus directed against?
The capsule
What is opsonisation?
Covering of the bacteria with immunoglobulins and complement
What was the first protein virulence determinant studied?
Pneumolysin
Describe the first demonstration of transformation
Live unencapsulated pneumococci (serotype 2) given to mouse –> no disease
Killed encapsulated pneumococci –> no disease
Live unencapsulated and killed encapsulated –> death
The live unencapsulated bacteria changed their phenotype by picking up DNA from the encapsulated bacteria
When was transformation first demonstrated?
In 1923 by Griffith
Describe the features of Optochin
What is it used for?
1911: effective in mice
1912: resistance emerges
1912: toxin in humans
Only used for detecting of pneumococci
Not used as antibiotic in humans
What are sulphonamides?
Describe the evolution
Antimicrobial
1938: efficacy shown
1943: emergence of resistance
What are the antimicrobials used against pneumococci?
Optochin
Sulphonamides
Penicillin G
Who discovered penicillin?
Alexander Fleming
What does multiple resistance mean?
The strain is resistant to three or more antimicrobial agents
What has happened with resistance to antimicrobial agents over the years?
More and more quickly, the bacteria are becoming resistant to the agents
What is the mechanism of action of penicillin G?
Targets Transpeptidase
Binds to this enzyme more strongly than the natural substrate
Prevents cross linking of peptidoglycan bricks
The cell wall can’t form
What are beta-lactams?
Antimicrobials such as penicillin g
What are penicillin binding proteins?
Transpeptidases
How does resistance to penicillin evolve?
Modified penicillin binding protein active site
Can still link the protein chains of the peptidoglycan
What does the clinical significance of resistance depend on?
• whether the bacterium is a pathogen
(Eg. If a commensal is resistant, it doesn’t matter)
- extent of resistance
- effect of resistance on outcome of treatment
What is the consolidation in the lung in lobar pneumonia
- Influx of fluid
- Neutrophils
- Bacteria
Which diseases does S. pneumoniae cause?
- Pneumonia
- Middle ear infection (otitis media)
- Meningitis
What is the relationship between amount of antimicrobials prescribed and resistance to the agent?
More prescription: more resistance
Which regions have a greater and lesser extent of resistance?
Most resistance:
• Africa
• Asia
• Spain
Less resistance: • Australia • USA • Netherlands • Sweden
How do we detect resistance in a lab?
- Dilution test
2. Diffusion tests
What things affect outcome of treatment?
- Type of infection (meningitis, septicaemia)
- Age
- Serotype of bacterium (more or less resistant)
- Co-morbidity
Describe MIC
What does this stand for?
Minimum inhibitory concentration
- Dilute the antibiotic out into tubes
- Add standard number of bacteria to each tube
- Incubate overnight
- Score for growth
- Look for the lowest concentration that provides resistance
