Week 2 - antimicrobials Flashcards
how can antibacterial agents be classified?
- bactericidal or bacteriostatic
- target site (mechanism of action)
- chemical structure (antibacterial class)
- spectrum (broad or narrow - action)
what are the different types of antimicrobials possible?
antibacterial
anti-fungal
antiviral
antiprotozoal agents
what are the ideal features of antimicrobial agents?
- selectively toxic
- few adverse effects
- reach site of infection (bloodstream / CSF)
- oral / IV formulation
- long 1/2 life (infrequent dosing)
- no interference with other drugs
what are the classes of antibacterials and their mechanisms of action? (what can the antibacterial affect?)
cell wall synthesis
protein synthesis
nucleic acid synthesis
cell membrane function
example of a drugs affecting cell wall synthesis?
beta-lactams
glycopeptides
example of drugs affecting protein synthesis?
tetracyclines
aminoglycosides
macrolides
example of drug affecting nucleic acid synthesis?
quinolones
examples of drug affecting cell membrane function?
(not as commonly used)
polymixins
how does penicillin work?
interfere with the protein which reinforces rigidity of cell wall (cross linkage) - inhibiting the growth of the cell
(penicillin binds to the protein which allows cross linkage)
how does vancomycin work?
sits on cross linking chains and prevents penicillin binding protein to join onto cross link to join them together - binds to the separate chains
How do Fluoroquinolones work?
bind to 2 nuclear enzymes, inhibiting DNA replication
affecting nucleic acid synthesis
what are the different mechanisms of resistance?
- drug inactivating enzymes
- altered target
- altered uptake
how do drug inactivating enzymes work?
microorganisms produces inactivating enzymes that destroys the antibiotic drug before it can act on the microorganism - enzyme destroys drug
what is an example of a drug inactivating enzyme?
B-lactamases
aminoglycoside enzymes
how do altered target resistance work?
target enzyme has lowered affinity for antibacterial
(the target for the activity of the organism is changed, so the antibiotic is no longer as effective because the target has changed)
what is an example of altered target resistance?
meticillin (MRSA)
how does altered uptake resistance work?
- decrease permeability
2. increase efflux
explain decreased permeability in altered uptake resistance
inability of antibiotic to penetrate into the cell - drug can’t get into cell
explain increase efflux of altered uptake
microorganism has an active pump which pumps the antibiotic out of the cell before it can take effect - efflux
drug sent out of cell via active pumping
example of decrease permeability and increase efflux?
- B-lactams
2. tetracyclines
what are the genetic basis of antibiotic resistance?
- chromosomal gene mutation
2. horizontal gene transfer
explain chromosomal gene mutation
mutated gene containing resistance in a cell survives antibiotic
antibiotic resistance selected and multiply and can be spread onto other patients to spread resistance
what are the different components that can take part in horizontal gene transfer?
- chromosome
- plasmid
- transposon
what are the different methods of horizontal gene transfer?
- conjugation
- transduction
- transformation
what is conjugation?
sexual process between 2 microorganisms - transfer
what is transduction and what does it use?
viruses that can affect microorganisms - phages
what is transformation?
free genetic material (e.g. DNA) that can pass directly through the cell wall into the organism
what are the different types of horizontal gene transfer that are passed onto the next generation of microorganisms?
- cell replication - plasmid
- plasmid integrated within the bacterial DNA, so when cell replicates, the integrated plasmid is replicated as well (plasmid integrated into nucleus)
what is the minimum inhibitory concentration (MIC)?
the minimum concentration of antibiotic required to inhibit bacterial growth
