All about Antibiotics and how their action!!

1. ANTIBACTERIAL AGENTS
I AM
ANTIBACTERIA..
I AM BACTERIA
…PLZ SPARE
ME….
BY: MINHAZ AHMED
Intgrated M.Sc 4th sem
BBI11014

2. What are antibacterial agents?
An antibacterial is an agent that inhibits bacterial growth or kills bacteria.
often used synonymously with the term antibiotic(s).
The term antibiotic was first used in 1942 by Selman Waksman.

3. WHY ANTIBACTERIALS?
Bacterial conjuctivities: pink eye
Bacterial Leaf Blight of soybean is
caused by the
bacterium Psuedomonas syringae
Skin spots by bacterial activities
Bacterial Canker

4. HOW ARE THEY CLASSIFIED?
on the basis of chemical/biosynthetic origin into
Natural (ex- penicillin)
 semisynthetic
 synthetic(ex-Sulfanilamide)
On biological activity; according to their biological effect on
microorganisms:
 bactericidal agents kill bacteria,
and bacteriostatic agents slow down or stall bacterial growth.

5. The bacterial cell
The success of antibacterial agents owes much to the fact that they can act
selectively
against bacterial cells rather than animal cells.
 This is largely due to the fact that
bacterial cells and animal cells differ both in their structure and in the biosynthetic
pathways which proceed inside them.

6. WHERE THEY WORK?
Rifamycins
Penicillins
Cephalosporins
cycloserine
capsule
Cell wall
cytoplasm
polymyxins
sulfonamides
Chloramphenicol
Streptomycin
tetracyclines
Ribosomes

7. MECHANISM OF ACTIONS
Inhibition of cell
wall synthesis
Penicillins
Cephalosphorins
Imipenem
Meropenem
Aztreonam
vancomycin
Inhibition of
bacterial protein
synthesis
Aminoglycosides
Chloramphenicol
Macrolides
Tetracycline
Streptogrmins
linezolid
Inhibition of
Nucleic Acid
Synthesis
Fluoroquinolones
Rifampin
Inhibition of
Folic Acid
Synthesis
Sulfonamides
Trimethoprim
Pyrimethamine

8. Inhibition of cell wall synthesis:
Penicillins, cephalosphorins, imipenem, meropenem, aztreonam,
vancomycin
bacteriocidal
Must have beta-lactum ring in them which binds and blocks
transpeptidases known as penicillin-binding proteins(PBP) which causes the
final cross links between the pentapeptides of peptidoglycan layer.
Mechanism of resistance:
Penicillin
Penicillinases: break the
beta lactam ring structure (
staphylococci)
Structural changes in PBP’s
(MRSA), S. pneumococci
cephalosporin
Change in porin structure:
concerns the gram negative
organism

10. Inhibition of bacterial protein synthesis
Aminoglycosides,Chloramphenicol,Macrolides,Tetracycline,Streptogrmins, Linezolid.
Bactericidal and bacteriostatic.
 The primary steps in the process that are attacked are
 the formation of the 30S initiation complex (made up of mRNA, the 30S ribosomal
subunit and formyl-methionyl-transfer RNA),ex Streptomycin (A-glycosides)
 the formation of the 70S ribosome by the 30S initiation complex and the 50S ribosome,ex
Kanamycin and tobramycin and
 the elongation process of assembling amino acids into a polypeptide.ex Lincomycin,
chloramphenicol.
RIBOSOME

11. Erythromycin:
Binds to 50S-rRNA &
prevents movement
along mrna

12. Mechanisms of resistance:
a mutation of ribosomal
binding site
enzymatic modification of
antibiotic
an active efflux of antibiotic
out of cell
Streptomycin

13. Inhibition of Nucleic Acid Synthesis
Fluoroquinolones(levofloxacin, norfloxacin),Rifampin
Bacteriocidal
Can inhibit DNA gyrase or RNA polymerase
Mechanism of resistance:
an alteration of alpha subunit of DNA gyrase
(chromosomal)
beta subunit of RNA polymerase (chromosomal) is
altered

14. Quinolones are a key group of antibiotics that interfere with DNA synthesis by
inhibiting topoisomerase, most frequently topoisomerase Iv and topoisomer ii (DNA
gyrase) , an enzyme involved in DNA replication. DNA gyrase relaxes supercoiled
DNA molecules and initiates transient breakages and rejoins phosphodiester bonds
in superhelical turns of closed-circular DNA. This allows the DNA strand to be
replicated by DNA or RNA polymerases.

15. Rifampicin blocks initiation of RNA synthesis by specifically inhibiting bacterial
RNA polymerase. It does not interact with mammalian RNA polymerases,
making it specific for Gram-positive bacteria and some Gram-negative
bacteria.
Mechanism of resistance:
an alteration of alpha subunit of DNA gyrase
(chromosomal)
beta subunit of RNA polymerase (chromosomal) is altered

16. Inhibition of Folic Acid Synthesis
Sulfonamides, Trimethoprim, Pyrimethamine
Bacteriostatic
Binds and blocks enzymes mainly pteridine synthesase, dihydrofolate
reductase responsible for folic acid synthesis.
What are Folic Acid?
Folic acid enzymes are nessary for the synthesis of amino acids, hence necessary for bacterial protein
synthesis.
Folic acid

17. Sulfonamide functional group
trimethoprim
Pyrimethamine
Pyrimethamine
Mechanism of resistance:
Mutations in the gene for
dihydrofolate reductase
decreasing binding affinity .

18. Some Side affects of antibacterial agents
ANTIBACTERIAL AGENTS
SIDE EFFECTS
Aminoglycosides
renal (kidney) toxicity, ototoxicity (hearing
loss), dizziness, nausea/vomiting,
nystagmus
Sulfonamides
nausea/vomiting, diarrhea, anorexia,
abdominal pain, rash, photosensitivity,
headache, dizziness
Tetracyclines
nausea/vomiting, diarrhea, anorexia,
abdominal pain, tooth discoloration in
children < 8 years, liver toxicity
Quinolones
nausea/vomiting, diarrhea, abdominal
pain, headache, lethargy, insomnia,
photosensitivity (can be severe)