Antibiotics 1 Flashcards
Describe the gram-stain?
Crystal violet stain is used to stain bacteria.
It is then washed with alcohol.
Gram-positives have a thicker peptidoglycan wall so stain darker.
Gram-negatives the stain is washed out more as the peptidoglycan wall is thinner and bacteria appear pink.
What bacteria have an inner cell membrane?
Gram positives and negatives.
Which bacteria have an outer cell membrane?
Gram negatives only.
What is the function of a bacterial outer cell membrane?
Bacterium can control access to the cell wall.
What bacteria have a periplasm?
Gram-negatives (although through positives have a thin one)
What is a periplasm?
A space of gel like matrix.Contains enzymes, protein folding, small molecule trafficking and the bacteria can put enzymes in which degrade antibiotics.
What is the advantage against antibiotics of having a periplasm?
The bacterium can put enzymes in the periplasmic space which degrade antibiotics. This is more concentrated than putting enzymes out to the neighbouring environment and more likely to protect the bacteria from destruction.
Name the antibiotic targets of bacteria?
- Cell wall peptidoglycan
- metabolism
- degrade DNA or prevent its replication
- Switch off protein production in the ribosome
Describe bactericidal antibiotic action?
Achieves sterilisation of the infected site by directly killing bacteria.
What is the downside of bactericidal antibiotic action?
Potentially the lysis of bacteria can lead to the release of toxins and inflammatory material.
Describe bacteriostatic antibiotic action?
Suppresses growth but doesn’t sterilise the site.
What is the downside of bacteriostatic antibiotic action?
Requires additional factors to clear bacteria e.g. the immune system.
This wouldn’t work in an immunocompromised host.
What are broad spectrum antibiotics?
Effective against a wide range of bacteria.
What is good about broad spectrum antibiotics?
Treat a wide range of causes of infection.
What is bad about broad spectrum antibiotics?
Can also target colonising bacteria which is good e.g. in the gut.
What are narrow spectrum antibiotics?
Active against a limited range of bacteria.
When would narrow spectrum antibiotics be used?
Only when the cause is well defined.
What is guided antibiotic therapy?
Where you identify the cause of infection and select an antibiotic based on sensitivity testing.
Use a narrow spectrum antibiotic.
Try limit drug to the site of infection.
Try have as little impact on colonisation and resistance as possible.
What is empirical therapy?
Have an educated guessed based on clinical findings/epidemiology.
Used when therapy cannot wait for culture.
Use a broad spectrum antibiotic.
This must penetrate throughout the body.
Accept there will be an impact on colonisation and resistance.
What is prophylactic therapy?
Used before an infection begins to prevent it.
List some ways antibiotic associated harm can occur?
Disruption of bacterial flora leading to overgrowth of yeasts (e.g. thrush) and overgrowth of bowel (e.g. diarrhoea).
Antibiotic use is also associated with c. diff colitis causing diarrhoea.
Host may get future colonisation and infection with resistant organisms.
Name the 4 classes of B-lactum antibiotics?
Penicillians
Cephalosporins
Catbapenems
Monobactams.
Which B-lactam antibiotic is the more narrow spectrum?
Penicillians.
Describe the mechanism of action of B-lactams?
Bind to transpeptidase enzymes which constructs the bacterial cell walls and interferes with crosslinking of peptidoglycan.
This causes lysis of bacteria (bacteriostatic).
What is a B-lacamase? How does it work?
Enzymes that lyse and inactivate beta-lactam drugs by hydrolysing the beta-lactam ring.
