To enjoy the presentation kindly download it. For Original view, download "Poetsen One" font style from dafont website. Here I have discussed mecahnism of action of penicillin (all beta lactam antibiotics)

1. Beta Lactam
Antibiotics

2. These are antibiotics having a beta-lactam ring.
The major groups are penicillins and
cephalosporins.
Monobactams and carbapenems
are relatively later additions.

3. PENICILLINS
Penicillin was the first antibiotic to be used
clinically in 1941.
It is a miracle that the
least toxic drug of its kind was the first to be
discovered.
Penicillin was originally obtained
from the fungus Penicillium notatum, but the
present source is a high yielding mutant of
P. chrysogenum.

4. Chemistry and properties
The penicillin
nucleus consists of fused thiazolidine and
beta-lactam rings to which side chains are attached
through an amide linkage.
Penicillin G (PnG), having a benzyl side chain at R
(benzyl penicillin), is the original penicillin
used clinically.

5. The side chain of natural penicillin can be
split off by an amidase to produce
6-aminopenicillanic acid.
Other side chains can then be
attached to it resulting in different semisynthetic
penicillins with unique antibacterial activities
and different pharmacokinetic profiles.

6. At the carboxyl group attached to the thiazolidine
ring, salt formation occurs with Na+
and K+.
These salts are more stable than the
parent acid.
Sod. PnG is highly water soluble.
It is stable in the dry state, but solution deteriorates
rapidly at room temperature, though it
remains stable al 4°C for 3 days.

7. Therefore,
PnG solutions are always prepared freshly.
PnG is also thermolabile and acid labile.
Unitage I U of crystalline sod. benzyl penicillin
= 0.6 μg of the standard preparation.
Accordingly,
I g = 1.6 million units or I MU = 0.6 g.

8. Mechanism of action
Al l beta-lactam antibiotics interfere with the
synthesis of bacterial cell wall.

11. When susceptible bacteria divide in the
presence of a beta-lactam antibiotic-cell wall
deficient (CWD) forms are produced.
Because the interior of the bacterium is
hyperosmotic,
the CWD forms swell and burst • bacterial
lysis occurs.
This is how beta-lactam antibiotics
exert bactericidal action.

12. Rapid cell wall synthesis occurs when the
organisms are actively multiplying;
beta- lactam antibiotics are more lethal in this
phase.
The peptidoglycan cell wall is unique to
bacteria.
No such substance is synthesized
by higher animals.
This is why penicillin is practically

13. In gram-positive bacteria, the cell wall is
almost entirely made of peptidoglycan, which is
>50 layers thick and extensively cross linked,
so that it may be regarded as a single giant
mucopeptide molecule.
In gram-negative bacteria,
the cell wall consists of alternating layers of
lipoprotein and peptidoglycan (each layer 1- 2
molecule thick with little cross linking).

14. This may be the reason for higher susceptibility of
the gram-positive bacteria to PnG.
Blood, pus, and tissue fluids do not interfere
with the antibacterial action of P-lactam
antibiotics.