2. Contents
• History
• Definition
• Difference between prokaryotic and
eukaryotic cell
• Mechanism of action of antibiotics
• Mechanism of bacterial resistance
• Principles of antibiotic dosing
4. • Chemotherapy
it means the treatment of systemic/ topical infection with
the drugs that have selective toxicity for an invading
pathogen or selectively destroy cancerous tissue without
harming the host cell
• it require proper dose
• Advantage of biochemical and physiological difference in
prokaryotes and eukaryotes
5. Antimicrobial agents
Antibacterial agents Antibiotics Semisynthetic antibiotics
Synthesized in
laboratory
Obtained from
fermentation of
microorganisms
Chemical structure derived
from microorganism then
modified by attaching
different chemical moieties
9. Mechanism of action of antibiotics
Inhibition of cell wall synthesis
Alteration of cell membrane integrity
Inhibition of ribosomal protein synthesis
Supression of DNA synthesis
17. Supression of DNA synthesis
inhibiting synthesis of folate, purine and pyrimidines
inhibiting DNA/ RNA polymerase
inhibiting DNA gyrase
directly damaging DNA and its functioning
21. By inhibiting DNA gyrase
DNA gyrase
introducing negative supercoils in DNA
cut both strands of DNA
reseal to avoid supercoiling
Fluoroquinolone
Eukaryotic cell do not contain DNA gyrase
23. Bacterial resistance to antibiotics
• Antibiotic
resistance: Defines as
microorganism that are not
inhibited by usually acheivable
systemic concentration of an
antimicrobial agent with normal
dosge schedule and / or fall in
the minimum inhibitory
concentration range
Why resistance occurs ?
• resistant organism lead to
treatment failure
• resistant bacteria may spread
in community
25. Genetic method of antibiotic resistance
Genetic method of antibiotic
resistance
Chromosomal
methods: mutation
Extrachromosomal
mechanism:
Plasmid
26. Mutation
• It refers to change
in DNA structure of
a gene
• occcurs at
frequency one per
million cells
• Sensitive bacteria
die but resistant
continue to grow
27. Plasmid
• extrachromosomal
genetic elements can
replicate indepedently
and freely in cytoplasm
• plasmid carry genes
resistant to antibiotic (r-
gene) are called R-
plasmids
• The r-gene transferred
from one R-plasmid to
another plasmid / to
chromosome
28. 1. Transfer of r-genes from one bacterium to another
a. Conjugation
b. Transduction
c. Transformation
2. Transfer of r-genes between plasmids within the
bacterium
a) By Transposons
b) By integrons
30. Transfer of r-genes between plasmids within the bacterium
Trasposons
transposons are sequence of
DNA that can move around
different positions within the
genome of single cell
The donor plasmid conatining
tansposons, co-integrate with
acceptor plasmid. They can
replicate during co-integration.
Both plasmids then seperate
and carrying r-genes
31. Integrons
Large mobile DNA
Packed with multiple gene casette, eachconsisting of
resistant gene attached to samll recognition site.
this genes encode several bacterial function like
resistance and virulence
32. Biochemical Mechanism
1. By producing an enzyme that inactivates the antibiotic
2. Prevention of drug accumulation in the bacterium
3. By modification/protection of the target site
4. Use of alternative pathways for metabolic/growth
requirements
5. By Quorum sensing(QS)
33. By producing an enzyme that inactivates the antibiotic
• beta-lactamase enzyme
Inactivation of
beta-Lactam
antibiotics
• chloramphenicol acetyl transferase
Inactivation of
chloramphenicol
• acetyl transferases
• phosphotransferases
• adenyltransferases
Inactivation of
aminoglycoside
34. Prevention of drug accumulation in the bacterium
Prevention of
drug
accumulation
alteration in
the bacterial
outer
membrane
active
transport of
drug ceases
active efflux
of drug
36. Use of alternative pathways for metabolic/growth
requirements
• resistance can occur by altering pathways
that bypasses the reaction inhibited by the
antibiotic
• Sulfonamide resistance can occur by
overproduction of PABA