8. Antibiotics Flashcards
define antibiotic
a substance that is selectively toxic to microorganisms
by what 3 ways can antibiotics be delivered
prescription, injection, IV drip
what does penicillin target
the peptidoglycan layer found in Gram-positive bacteria, making the cells leaky and fragile
how does gentamicin work, what is a limitation of this
inhibits pathways found in human cells
limitation: causes side effects
by what 3 factors can we classify antibiotics
chemical structure
spectrum of activity
mode of action
name a beta-lactam antibiotic
penicillin
what does bacteriostatic mean
agents that prevent the growth of bacteria
what does bactericidal mean
agents that kill bacteria
name two differences between bactericidal and bacteriostatic agents
bactericidal agents are irreversible, bacteriostatic are reversible
bactericidal agents do not involve the immune system , bacteriostatic agents work with the immune system to prevent growth
name 3 modes of action for antibiotics
- inhibit protein synthesis
- inhibit cell wall synthesis (penicillin)
- inhibit pathogen adhesion to host cells
who discovered penicillin
Alexander Fleming
what is penicillin’s mode of action
bactericidal
- bind to and destroy cell walls by inhibiting cross-link formation = lysis
what can penicillin be used to treat
wide spectrum of infections, e.g. chest infections
what can be a side effect of penicillin use
allergic reactions
describe resistance to penicillin
relatively common:
beta-lactamase in restraint bacteria destroy pencillin’s beta-lactam ring = no effect on bacteria and cell wall formation
why is ampicillin a better beta-lactam antibiotic
contains beta lactamase inhibitor = destroy reisstant bacteria, so applicable to a variety of infections
what group of antibiotics does gentamicin belong to
aminoglycosides
how do aminoglycosides work?
bactericidal:
- bind to ribosomes preventing protein synthesis
name 3 Gram negative bacteria
e.coli, pseudomonas, klebsiella
name 2 Gram positive bacteria
streptococci
staphylococci
what do aminoglycosides target
mainly Gram-negative bacteria
how can aminoglycosides be used to treat Gram positives
used in combination with Beta-lactam antibiotics
what infection are aminoglycosides commonly used to treat
UTIs
what is a side effect of aminoglycosides
hearing loss
how are aminoglycosides administered
in IV drip
how does resistance emerge in aminoglycosides , give an example
mutations to ribosome binding site, e.g. streptomycin = no longer fits in the binding site
how do tetracyclines work
bacteriostatic
bind to 30S subunit to prevent rRNA binding to the A site =
prevents bacterial protein synthesis
what can tetracyclines be used to treat
Gram-positive bacteria
diseases such as lymes disease
how are tetracyclines administered, what can inhibit their absorption
administered orally
- absorption inhibited by dairy (bind to calcium forming an insoluble complex)
what is a side effect of tetracyclines
photosensitivity to sunlight
how have bacteria cells become resistant to tetracycline
efflux resistance genes:
pump tetracycline out of the cell faster than its uptake
what are ribosomal protection proteins
tet (M), tet (O) ….
bind to ribosome changing its conformation - prevents tetracycline from binding without stopping synthesis
what is the effect of the tet (X) gene
produces a cytoplasmic protein that chemically modified tetracycline in the presence of oxygen and NADPH
describe MRSA in england
significant decrease in resistant strain, this is due to better cleaning regimes, screening and hand washing practises
