Cell wall synthesis inhibitors: Penicillins Flashcards
What do all beta-lactams have in common?
The beta-lactam ring in their structure
What are bacterial cell walls made of?
Peptidoglycan or muerin
What are peptidoglycan made of?
Long strands of amino polysaccharides running in parallel. Also made of segments of NAG and NAM in alternating pattern to make a long chain
What protrudes from the peptidoglycan chain?
At the tips of the NAM subunits are tetrapeptide and pentapeptide chains, protruding from NAM subunits.
What is the role of the peptide chains that protrude from the NAM subunits?
They link other peptide chains from neighbouring strands through transpeptidation
What enzyme is responsible for transpeptidation?
PBP- penicillin binding proteins
How do beta-lactams distrupt the cell wall synthesis?
They have a similar structure to the tetrapeptide chains, so the PBP enzyme mistakenly binds to the beta-lactam molecule which disables the enzyme meaning the cell wall becomes weak and unstable
What happens to the bacteria if tries to multiply after a beta-lactam is introduced?
The cell wall will collapse- killing the bacteria
How has MRSA developed to resist beta-lactams?
It developed an enzyme called beta-lactamase which breaks down the beta-lactam ring in the antibiotic, disabling it
How has the development of beta-lactamase been tackled?
By adding a beta-lactamase inhibitor such as clavulanic acid. Or development of a new antibiotic called methicillin which has a large side chain that does not fit in beta-lactamase
How did MRSA further develop to be resistant?
It change the active site shape of the PBP enzyme so even if beta-lactamase did not work, the antibiotic can not fit in PBP
What have we resorted to, to treat MRSA?
Reserved antibiotics belonging to the glyco-peptide antibiotics like vancomyocin and teicoplanin
What are some examples of narrow spectrum penicillins?
Penicillin G or Benzylpenicillin sodium (IV) and Penicillin V or phenoxymethylpenicillin (PO)
What are narrow spectrum penicillins still used for?
Common gram positive bacteria: streptococcus pyogenes (pharyngitis)
Gram negative bacteria: neisseria meningitidis (bacterial meningitis)
Spirochetes: teponema pallidum (syphilis) or borrelia burgdorfei (Lyme disease)
Are narrow spectrum penicillins susceptible to beta latctamase?
Yes
What bacteria are resistant to narrow spectrum penicillins?
A lot of gram-ngeative aerobes and some bacteria they used to treat like: S.aureus, Streptococcus pneumonia and neisseria gonorrhoeae
What are examples of broad spectrum beta-lactamase susceptible medication?
Amoxicillin and ampicillin
What bacteria are broad spectrum beta-lactam antibiotics effective against?
Wider range of gram negative e.g.:
-Haemophilus influenzae, moraxella catarrhalis (cause resp infections and pneumonia)
-H.pylori
-Salmonella shigella and listeria (diarrhoea)
(and the same gram positive treated by penicillin but they are less potent)
Why is listeria particularly bad in pregnancy and babies?
It can lead to meningitis
What pregnancy category are these class of antibiotics?
Category B, meaning no risks found in pregnancy
Which antibiotic is particularly used in pregnancy?
Amoxicillin
What are some examples of extended spectrum pencillins?
Piperacilin and ticarcillin
What are extended spectrum penicillins most notably effective against?
Pseudomonas aeruginosa
What are very narrow spectrum beta-lactamase resistant medication?
They are antibiotics made to fight bacteria like S.aureus and S.epidermis. They are also known as antistaphyloccocal penicillins.
