Antibiotics Flashcards
How can you categorise antibiotics and how they work?
According to effect on the cell:
* cell wall synthesis
* protein synthesis
* nucleic acid synthesis
Cell wall
Interferes with peptidoglycan synthesis - building bricks
* beta lactams - penicillins, flucloxacillin and cephalosporins
* carbapenems - meropenem
Incorporation of glycan subunits - laying bricks
Protein synthesis
30s
- aminoglycosides - bacterialcidal
- tetracyclines - bacteria static
50s
- macrolide - erythromycin
Nucleic acid synthesis
DNA gyrase
- quinolones - ciprofloxacillin
- metronidazole - affects DNA synthesis
RNA polymerase
Affects RNA transcription
- rifampicin
Folate synthesis
- trimethoprim
Draw a bacterial cell
- plasmid - coil of dna - with specialised genes confering certain functions - e.g. antibiotic resistance
- no nucleus
- cell wall
- 30/50s ribosomes - protein synthesis
- DNA gyrase - synthesise DNA
- RNA polymerase - synthesises protein
- flagellum - helps movement
- pili - attachment
What is a narrow therapeutic window mean?
Narrow window between effective doses and adverse toxic effects.
Difference between allergy, sensitivity and intolerance?
- Allergy - an immune system reaction to a substance
- Sensitivity - no immune response
- Intolerance - the body lacking a chemical or enzyme needed to digest certain food
What is a biofilm?
- a community of bacteria located below of a layer of glycocalyx
- glycocalyx - is a polysaccharide matrix of both glycoproteins and glycolipids
Mechanism
- planktoic bacteria -settle on surface esp metal
- start to creat a glycocalyx layer - dome
- difficult to eradicate - abx can’t penetrate
- needs debridement
How do you perform a gram stain?
3 stages
1. crystal violet indium dye
2. alcohol rinse
3. saffranin O
crystal violet indium dye
Bacteria soaked in the dye
Alcohol rinse
Wash in an alcohol rinse
Saffranin O
Gram positive bacteria retain the blue colour but gram negative doesnt
counter stain with saffranin O to dye them pink
What is mrsa and masa?
MRSA - methillin resistant staphylococcus aureus
- confers the mecA gene
- mecA is the gene for the penicillin binding protein
- adept at forming biofilms
Risk factors for colonisation:
- skin lesions
- old age
- previous hospital or prolonged hospital
- chronic illness
- invasive indwelling device
- prolonged antibiotics
- exposure to exposed
treatment
- vancomycin
- teicoplanin - good bone penetration
- both work on cell wall
MSSA - methicllin sensistive staph aureus
similar to MRSA but differs in it’s antibiotic resistance
treated with daptomycin
Which antibiotics affect the cell wall
Beta lactams
- penicillins
- flucloxacillin
- cephalosporins - cephtriazone
Carbapenems
- meropenem
which antibiotics affect protein synthesis
30s
- aminoglycosides - gentamicin
50s
- macrolide - erythromycin
Which antibiotics affect nucleic acid syntheos
DNA gyrase
* ciprofloxacillin
- metronidazole
RNA polymerase
- rifampicin
what antibiotic do you use for your arthroplasty?
flucloxacillin - affects cell wall
gentamicin - affects the ribosomal 30s subunit
what are the gram positive bacteria?
Gram +ve cocci
- staph
- strep
- enterococcus
Gram +ve bacilli
- spore - clostridium
- non-spore forming - listeria
what are the gram negative bacteria?
gram -ve cocci
- neisseria
gram -ve bacilli
- Ecoli
* haemophilus influenzae
* salmonella
* pasteurella
* brucella
how do bacteria confer antibiotic resistance?
B-lactamase
- hydroxylates penicillin
* clavulanic acid - inhibits
Mec A - in MRSA
- produces enzymatic binding protein
- prevents antibiotic enzyme function
Biofilm
- staph
- salmonella
Altered cell permeability
- resists tetracyclines
how do you eradicate MRSA?
Routine preoperative screening
- nasal, groin and axilla
- 20% patients carry staph and 5% MRSA
- 3 negative swabs before surgery
- eradicate with 4% chlorhex bathing and nasal mucopirocin for 5 days then reswap and repeat if needed
