Antibiotics 2 Flashcards
what are the components of pencillin structre?
- Amide bond
- Bicyclic structure
- Stereochemistry
- Lactam
- free acid
- Thiazolidine ring
How many types of PBPs (penicillin binding protein) do bacteria have?
- 5 types
B-lactams acylate the cative site serine residue of PBPs to inhibit transpeptidation. TRUE OR FALSE?
TRUE
PBPs have differing affinities for B-lactams. true or flase?
true
How is optimum antibacterial effects achieved?
- Through binding to multiple types of PBPs
how can resistance be mediated with PBPs?
- Through mutated PBPs
what are the two modes of action of penicillin?
- Transpeptidase cross linking - PBP catalyses release of D-Ala from pentapeptide
- Penicillin inhibition - penicillin binds irreversibly to PBP enzyme
penicillin G is non-toxic. TRUE OR FALSE?
TRUE
what type of bacteria is pencillin G active against?
- Gram negtaive
- Gram positive - but not broad spectrum
what are the drawbacks of penicillin G?
- Allergies are observed
- Not orally active
- Acid sensitive
- Destroyed by b-lactamases
B-lactam is extremely reactive, unlike tertiary amide. true or false?
true
why is penicillin G acid sensitive?
- the acid catalysed ring is opened and relieves the ring strain imposed by fusing a 4-memebered ring to a 5-memebered ring
- Participation from the side chain opens the lactam
why is the side chain of pencillin V (5) unlikely to react with the b-lactam ring?
- Due ot electronic effects
what are soem properties of pencillin V?
- Acid stable
- Can be taken orally, but now is sensitive to b-lactamases
- Less potent than penicillin G
Resistance of b-lactamases is transferable between strains. treu ro false?
true
Gram negative bacteria do not have b-lactamases within the periplasmic space surrounding the cell. true or false?
true
how is lactamase resistance obtained?
- They attach bulky groups that prevent access to the enzyme active site
Such b-lactamases resistant penicillin have little or no effect against gram negative bacteria. true or false?
true
what are B-lactamases?
- they are enzymes produced by bacteria that provide multi-resistance to B-lactam antiiotics such as penicillin
Methicilin is resistant to b-lactamases, but is active sensitive so not orally active. true or flase?
true
what type of bacteria is methiciliin effective for?
- weakly effective in gram positive
- But not effective in gram negative and MRSA
Between oxacillin, cloxacillin, Dicloxacillin and flucloxacillin, which has the highest bioavailability?
- Flucloxacillin
oxacillin, cloxacillin, Dicloxacillin and flucloxacillin are stable to acid and b-lactamases. true ro false?
true
Give examples of broad/extended spectrum penicillins?
- Ampicillin
- Amoxycillin