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. 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.
4. 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.
5. WHERE THEY WORK?
Rifamycins
Cell wall
Penicillins
Cephalosporins
cycloserine
polymyxins
sulfonamides
Chloramphenicol
Streptomycin
tetracyclines
Ribosomes
capsule
cytoplasm
6. MECHANISM OF ACTIONS
Inhibition of cell
wall synthesis
Inhibition of
bacterial protein
synthesis
Inhibition of
Nucleic Acid
Synthesis
Inhibition of
Folic Acid
Synthesis
Penicillins
Cephalosphorins
Imipenem
Meropenem
Aztreonam
vancomycin
Aminoglycosides
Chloramphenicol
Macrolides
Tetracycline
Streptogrmins
linezolid
Fluoroquinolones
Rifampin
Sulfonamides
Trimethoprim
Pyrimethamine
7. 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
cephalosporin
Penicillinases: break the
beta lactam ring structure (
staphylococci)
Structural changes in PBP’s
(MRSA), S. pneumococci
Change in porin structure:
concerns the gram negative
organism
8.
9. 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
12. 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
13. 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.
14. 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
15. 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