This document discusses antibiotics that target peptidoglycan in bacterial cell walls. It begins by defining antibiotics and explaining where they come from, primarily fungi and bacteria. It then describes different classes of antibiotics that inhibit cell wall synthesis, including penicillins, cephalosporins, and vancomycin. These antibiotics contain beta-lactam rings or other structures that inhibit the enzymes responsible for cross-linking peptidoglycan during cell wall formation. As bacteria require their cell walls for structural integrity, these antibiotics selectively kill bacteria by preventing cell wall synthesis during growth and division.

1. PEPTIDOGYLCAN SPECIFIC
ANTIBIOTICS
SUBMITTED TO Dr. SASHI NAYYAR
SUBMITTED BY RAHUL DAGAR

2. WHAT IS AN ANTIBIOTIC?
 An antibiotic is a selective poison.
 It has been chosen so that it will kill the desired
bacteria, but not the cells in your body. Each
different type of antibiotic affects different bacteria
in different ways
 Substances produced by various species
of microorganisms: bacteria, fungi, actinomycetes-
to suppress the growth of other microorganisms
and to destroy them

3. WHERE DO ANTIBIOTICS COME FROM?
 Several species of fungi including Penicillium and
Cephalosporium
 E.g. penicillin, cephalosporin
 Species of actinomycetes, Gram positive filamentous
bacteria
 Many from species of Streptomyces
 Also from Bacillus, Gram positive spore formers
 A few from myxobacteria, Gram negative bacteria
 New sources explored: plants, herps, fish

4. ANTIBACTERIAL AGENTS
 A. Inhibitors of cell wall synthesis
 1. Penicillins
 2. Cephalosporins
 3. Other antibacterial agents that act on cell walls
 B. Disrupters of cell membranes
 1. Polymyxins
 2. Tyrocidins
 C. Inhibitors of protein synthesis
 1. Aminoglycosides
 2. Tetracyclines
 3. Chloramphenicol
 4. Other antibacterial agents that affect protein synthesis
 a. Macrolides
 b. Lincosamides
 D. Inhibitors of nucleic acid synthesis
 1. Rifampin
 2. Quinolones
 E. Antimetabolites and other antibacterial agents
 1. Sulfonamides
 2. Isoniazid
 3. Ethambutol
 4. Nitrofurans

5. ANTIBIOTIC MECHANISMS OF ACTION

6. BACTERIAL CELL WALLS
 Except for Mycoplasma and relatives, all bacteria of the
Domain Eubacteria possess peptidoglycan
 Peptidoglycan provides shape and structural support to
bacterial cells
 Bacterial cytoplasm is generally hypertonic compared to their
environment
 Net flow of water: into cell
 Wall under high osmotic pressure
 Chemical structure of peptidoglycan contributes to its function
 Polysaccharide chains composed of 2 alternating sugars, N-
acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
 Cross-linked in 3 dimensions with amino acid chains
 A breach in peptidoglycan endangers the bacterium

7. PEPTIDOGLYCAN MOLECULE
Cross links are both horizontal and vertical between glycan chains
stacked atop one another.

8. There is no molecule similar to
peptidoglycan in humans,
making drugs that target cell
wall synthesis very selective in
their toxicity against bacteria

9. GRAM POSITIVE & GRAM NEGATIVE
 Gram positive bacteria have a thick cell wall
 Peptidoglycan directly accessible from environment
 Gram negative bacteria have a different wall
 Thin layer of peptidoglycan
 Surrounded by an outer membrane composed of
lipopolysaccharide, phospholipids, and proteins
 Outer membrane is a barrier to diffusion of molecules
including many antibiotics
 Some hydrophobic antibiotics may diffuse in.
 Porins allow passage of only some antibiotics

10. INHIBITION OF CELL WALL SYNTHESIS
 beta-lactam containing antibiotics inhibit
transpeptidase; bacteria cannot synthesize
reinforced cell wall and they lyse when they try to
grow
 Vancomycin and cyclo-Ser inhibit specific binding of
Ala’s in crossbridges to transpeptidase in many
gram+ bacteria
 Bacitracin inhibits secretion of NAG and NAM
subunits
 All of these only kill growing bacteria

11. PENICILLINS
 Penicillins contain a b-lactam ring which
inhibits the formation of peptidoglycan
crosslinks in bacterial cell walls (especially in
Gram-possitive organisms)
 Penicillins are bactericidal but can act only on
dividing cells
 They are not toxic to animal cells which have no
cell wall

12. CEPHALOSPORINS
 They also owe their activity to b-lactam ring and are
bactericidal.
 Produced from a fungus Cephalosporium
acremonium.
 Good alternatives to penicillins when a broad -
spectrum drug is required
 should not be used as first choice unless the
organism is known to be sensitive

13. VANCOMYCIN
 This interferes with bacterial cell wall formation and
is not absorbed after oral administration and must
be given parenterally.
 It is excreted by the kidney.
 It is used i.v. to treat serious or resistant Staph.
aureus infections and for prophylaxis of
endocarditis in penicillin-allergic people.

14. THANKS