Penicillin and other beta-lactam antibiotics work by inhibiting the final step of bacterial cell wall synthesis (transpeptidation or cross-linkage). This exposes the cell membrane which is structurally less stable. They inactivate bacterial enzymes called penicillin-binding proteins that are involved in cell wall synthesis and maintenance of cell morphology. Cephalosporins have a similar mechanism of action, inhibiting cell wall synthesis and activating autolysin enzymes. Carbapenems have broad-spectrum activity and are resistant to beta-lactamases. Vancomycin inhibits cell wall synthesis by binding to the D-alanyl-D-alanine portion of peptidoglycan precursors.

2. echanism of acti
of Antibiotics
presentation
ology 2
mtaz Ali
Microbiology: federal Urdu university

3. Mechanism of actio
of antibioticsg to mechanism of action antibiotics are classified
ll synthesis Inhibitor
n synthesis inhibitor
acid synthesis inhibitor
mbrane synthesis inhibitors
te drugs

4. Cell wall inhibitor
inhibitor are that antibiotics that inhibit synthese
kill bacteria these antibiotics are bactericidal in n
further classified into four groups
β) lactam antibiotics
cin
mycin
rine

6. ta lactam antibiot
ntibiotics (beta-lactam antibiotics) are a class
ic consisting of all antibiotic agents that contain a beta-lacta
ular structures.
m antibiotics are further classified into four groups
sporin
nam
am

7. Beta lactam antibiotic

8. Mechanism of action of
Penicillin
nicillin interfere with the last step of bacterial cell wall sy
eptidation or cross-linkage), resulting in exposure of the
cally less stable membrane.
icillin-binding proteins: Penicillin inactivate numerou
bacterial cell membrane. These penicillin-binding protein
terial enzymes involved in the synthesis of the cell wall a
nance of the morphologic features of the bacterium. Exp
ntibiotics can therefore not only prevent cell wall synthe
ad to morphologic changes or lysises of susceptible bacte

10. Spectrum of Penicillin
n-binding proteins: Penicillin also inactivate numerous prote
ell membrane. These penicillin-binding proteins (PBPs) are bacter
the synthesis of the cell wall and in the maintenance of the mor
the bacterium. Exposure to these antibiotics can therefore not o
nthesis but also lead to morphologic changes or lyses of suscepti
r of PBPs varies with the type of organism. Alterations in some o
de the organism with resistance to the penicillins.
n of transpeptidase: Some PBPs catalyze formation of the
tween peptidoglycan chains . Penicillins inhibit this transpeptida
hus hindering the formation of cross-links essential for cell wall in

11. Spectrum of Penicillin
ral penicillins: Natural penicillins (penicillin G and penicillin V
ed from fermentations of the fungus Penicillium chrysogenum. Pe
-penicillin) is the cornerstone of therapy for infections caused by
m-positive and gramnegative cocci, gram-positive bacilli, and spiro
ins are susceptible to inactivation by β-lactamases (penicillinases
ed by the resistant bacteria. Despite widespread use and increas
nce to many types of bacteria, penicillin remains the drug of choi
ent of • gas gangrene (Clostridium perfringens) and • syphilis (Tr
m). • Penicillin V has a similar spectrum to that of penicillin G • P
cid stable than penicillin G and is often employed orally in the tre
ons.

12. Spectrum of Penicillin
aphylococcal penicillins: Methicillin •Nafcillin • oxaci
llin • are β-lactamase (penicillinase)-resistant penicillins. • Their
o the treatment of infections caused by penicillinase-producing
cci, including methicillin sensitive Staphylococcus aureus (MSSA)
urrently a source of serious community and nosocomial (hospita
nd is resistant to most commercially available β-lactam antibioti
e- resistant penicillins have minimal to no activity against gram-n

13. Spectrum of Penicillin
ed-spectrum penicillins: • Ampicillin and • amoxicillin • have an
al spectrum similar to that of penicillin G but are more effective aga
cilli • These extended-spectrum agents are also widely used in the
ry infections, • amoxicillin is employed prophylactically by dentists
the prevention of bacterial endocarditis.
seudomonal penicillins: • Piperacillin and • ticarcillin]• are
monal penicillins because of their activity against Pseudomonas
ents are available in parenteral formulations only. • Piperacillin is
hese antibiotics. • They are effective against many gram-negative
Klebsiella because of its constitutive penicillinase. • Formulation
r piperacillin with clavulanic acid or tazobactam, respectively, ext
al spectrum of these antibiotics to include penicillinase-producin
for example, most Enterobacteriaceae and Bacteroides species).

14. Cephalosporin
alosporins are bactericidal. • Cephalosporins same as pe
cell wall synthesis in a manner similar to penicillins • Inhi
ptidation • Activation of autolysin enzymes • Lysis of bac
different proteins than those which bind penicillin. PBP-

15. Carbapenem
nems are a class of beta-lactam antibiotics with a broad s
cterial activity. They have a structure that renders them
to betalactamases. Carbapenem antibiotics were origina
ed from thienamycin, a naturally-derived product of Strep
m Broad spectrum, covers Gram-positive, Gram-negativ
g ESBL-producing strains), Pseudomonas and anaerobes
nem Less seizure-inducing potential, can be used to tre
s Ertapenem Lacks activity vs. Acinetobacter and
monas Has limited activity against penicillin-resistant
cocci

16. Aztreonam

17. Mechanism of actio
Bacitracincin inhibits the synthesis of the bacterial cell wall by prev
nsport of peptidoglycan precursors through the cytoplasm
ane. Bactericidal It is bactericidal to Gram-positive bacte
s little activity against Gram-negative organisms.
cin interferes with the dephosphorylation of C55-isopren
osphate, and a related molecule known as bactoprenol
osphate; both of these lipids function as membrane carr
les that transport the building-blocks of the peptidoglyc
al cell wall outside of the inner membrane

19. echanism of action
Vancomycinmycin is an antibiotic produced by Streptococcus orientali
atopsis orientalis. With the exception of Flavobacterium
nly aginst gram-positive bacteria. Vancomycin is a glyc
cular weight 1500 dalton . It is water soluble and quite s
mycin inhibits cell wall synthesis by binding firmly to the D
us of nascent peptidoglycan pentapeptide . This inhibits
cosylase, preventing further elongation of peptidoglycan
king. The peptidoglycan is thus weakened, and the cell
ible to lysis. The cell membrane is also damaged, which
utes to the antibacterial effect.

21. Mechanism of action
Cycloserinerine • Originally discovered by Streptomyces • Now man
chemical synthesis • Interefere with synthesis of peptid
eptidoglycan • Specifically it inhibits both alanine racem
l-D-alanine synthetase
rine works as an antibiotic by inhibiting cell-wall biosynt
a. As a cyclic analogue of D-alanine, cycloserine acts agai
enzymes important in the cytosolic stages of peptidoglyc
is: alanine racemase (Alr) and D-alanine:D-alanine ligase