Antibiotics & Antimicrobials Flashcards
Define antibiotic
Substance produced by microorganisms or synthetically which posses the property of inhibiting the growth of or destroying other microoganisms
What is a bacteriostatic antibiotic? Give examples
Prevent the growth or reproduction of microorganisms in the host = leaving body’s natural defence mechanism to overcome infection
e.g. Tetracyclines, erthromycin, sulphonamides
What is a bacteriocidal antibiotic? Give examples
Inhibit the multiplication of the organisms but also kill bacteria even in the presence of pus
e.g. penicillin, streptomycin & cephalosporins
Give examples of broad spectrum antibiotics
Tetracycline, ampicillins and caphalosphorins (against gram +/- bacteria)
Give examples of narrow spectrum
Penicillin (gram +ve)
Who accidentally discovered penicillin ?
Alexandra Flemming 1929
Who first investigated, mass produced and sold penicillin?
Howard Florey & Ernist Chain 1940
What are the uses of antibiotics in dentistry?
- Theraputic e.g. acute odontogenic infections that aren’t amenable by immediate dental tx
- Prophylaxis - prevention of distant infection or wound infection (e.g. risk to infetive endocarditis)
When shouldn’t antibiotics be used in dentistry?
- Inflammatory conditions (post op oedema)
- Fibrinolytic conditions (e.g. dry sockets)
- Non-bacterial condtions (e.g. viral/fungal infections)
What is penicillin (beta-lactams) & glycopeptides more of action?
Interfere with cell wall synthesis: if cell wall is not intact = cell fragility & bacteriolysis = bacteriocidal
How are the cell walls in gram +/ gram - bacteria different?
- Gram + have multple peptidoglycan layers in cell wall
- Gram - have a single layer of peptidoglycans.
What is a peptidoglycan?
-consists of chains of alternating amino sugars which are crosslinked via peptide side chains of N-acetylmuramic acid.
What is the biosynthesis of bacterial peptidoglycan?
- Glycan unit formed (from N-acetylmuramic acid, N-aceytlglucosamines & 5x amino acids)
- Glycan unit is transported across cytoplasmic membrane & incorporated into the cell wall (by cell wall acceptors- transglycosylation)
- Peptides from one layer join to another by peptide cross-links (transpeptidation) - enzymes involved transpeptidase also known as peniciliin binding sites (PBS)
How does penicillin and cefalosporins work as an antimicrobial ?
Interferes with cell was synthesis
- inhibits enzymes (PBS) responsible for cross linking between chains
- inactivate autolysin inhibitors of bacteria thus autolysin is produced which creates defects in the cell wall by hydrolysing components
What is the anitbacterial spectrum of cefalosporins?
Broad spectrum for gram +/- bacteria
Give an example of a glycopeptide?
Vancomycin
How do glycopeptides interfere with cell wall synthesis?
-Prevent gylcan groups moving from cell membrane to cell wall=weakening cell wall
What are glycopeptides used for?
- Used to treat serious infections e.g. staphylococcal infections ( where the patient is allergic to penicillin
- Clostridium difficile
- Effective against aerobic /anaerobic gram +ve bacteria
Which antimicrobials inhibit protein synthesis?
- erythromycin
- tetracycline
- clindamycin
- the aminoglycosides
- fusidic acid
What antimicrobials attach to the 30s subunit?
Tetracycline, streplomycin & gentamycin
What anitmicrobials attach to the 50s subunit?
erythromycin & chlorampheniol
How does erythromycin work as an antimicrobial?
- Binds to 50s subunit
- interferes with translocation of protein synthesis
- as interferes with translocation = give rise to resistant mutations
How does tetracycline & fusidic work as antimicrobials?
-Binds to 30s -blocking entry to tRNA complexes to their functional location on the ribosome
How does clindamycin (lincosamide) work as an antimicrobial?
-Binds to 50s subunit = premature dissociation of peptidyl tRNA from the ribosomes.
