31. Antibiotics and anti-fungals Flashcards
outline the key features of bacteria
- single-cell microorganisms
- they have a cell wall and cell membrane
- they have an entire phylogenetic domain
- 1/3 are pathogenic
describe the key features of gram + bacteria and give an example
prominent, thick peptidoglycan cell wall
e.g. staphylococcus aureus
describe the key features of gram - bacteria and give an example
outer membrane with lipopolysaccharide
e.g. E-coli
describe the key features of mycolic bacteria and give an example
outer mycolic acid layer
e.g. mycobacterium tuberculosis
how is an important protein in prokaryotic nucleic acid synthesis made?
dihydropteroate (DHOp) is produced from paraaminobenzoate (PABA) by DHOp synthase and converted into dihydrofolate (DHF). DHF reductase then converts DHF into tetrahydrofolate (THF) which is important in DNA synthesis
what important protein is involved in prokaryotic DNA replication?
DNA gyrase (topoisomerase) releases tension from the DNA molecules, allowing DNA replication to occur
what important protein is involved in prokaryotic RNA synthesis?
RNA polymerase produces RNA from a DNA template
what important structures are involved in prokaryotic protein synthesis?
ribosomes
RNA molecules go through prokaryotic ribosomes which produce protein from RNA templates
what prevents dihydropteroate (DHOp) from being made? how successful is it?
sulphonamides inhibit DHOp synthase
the vast majority of bacteria are resistant to sulphonamides
what prevents tetrahydrofolate (THF) from being made?
trimethoprim inhibits DHF reductase
what interferes with DNA replication?
fluoroquinolones inhibit DNA gyrase and topoisomerase IV
what inhibits RNA polymerase? what does this result in?
rifamycins
bacterial death because there is reduced production of proteins required for bacterial cell survival
what are bacterial ribosomes inhibited by?
- aminoglycosides (e.g. gentamicin)
- chloramphenicol
- macrolides (e.g. erythromycin)
- tetracyclines
what type of bacteria are most susceptible to drugs and why?
gram - bacteria because they don’t have a prominent cell wall like gram + bacteria
what occurs in step 1 of bacterial wall synthesis - peptidoglycan synthesis?
- a pentapeptide is created on N-acetyl muramic acid (NAM)
- N-acetyl glucosamine (NAG) associates with NAM forming peptidoglycan
what occurs in step 2 of bacterial wall synthesis - peptidoglycan transportation?
- peptidoglycan is transported across the cell membrane by a bactoprenol molecule
- once it is in the periplasm, it undergoes a few steps before being incorporated into the bacterial wall
what occurs in step 3 of bacterial wall synthesis - peptidoglycan incorporation?
- it is incorporated into the cell wall
- transpeptidase enzyme cross-links peptidoglycan pentapeptides
what inhibits peptidoglycan synthesis?
glycopeptides (e.g. vancomycin) which bind the pentapeptides and prevent synthesis
what inhibits peptidoglycan transportation?
bacitracin inhibits bactoprenol regeneration
what inhibits peptidoglycan incorporation?
b-lactams (e.g. carbapenems, cephalosporins, penicillins) bind covalently to transpeptidase, inhibiting peptidoglycan incorporation into cell wall
what inhibits cell wall stability in gram + and gram - bacteria?
lipopeptides (e.g. daptomycin) disrupt gram-positive walls
polymyxins bind to lipolysaccharides (LPS) and disrupt gram-negative cell membranes
what are the causes of antibiotic resistance?
- unnecessary and inappropriate prescription
- livestock farming
- lack of regulation (available OTC in some countries)
- lack of development (in recent years)
what are beta-lactamases and what do they do?
they are destruction enzymes produced by bacteria
they hydrolyse the C-N bond of the beta-lactam ring in beta-lactam antibiotics
what types of antibiotics are more effective in gram + bacteria?
penicillins G and V
