Drug Resistance, Mechanism of Drug Resistance, Genetic Determinants of Drug Resistance, Level of Drug Resistance

2. M. Adeel Razzaq
Nayya Waseem Dar
Drug Resistance
Ph.D. Biochemist
HEC Research Scholar
University of Agriculture, Faisalabad
Pakistan
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3. • “Drug is any substance that when taken into the living organism may modify one or more of its
functions”.
• Drug discovery in the past often resulted from observations of the effects of plant extracts or individual
chemicals on animals or humans with no knowledge of the drug’s mechanism or site of action
• Today’s approach relies more on high-throughput screening of libraries containing hundreds of
thousands or even millions of compounds for their capacity to interact with a specific molecular target
• Crucial questions arise:
❑ Can one find a drug that will have the desired effect against its target?
❑ Does modulation of the target protein affect the course of disease?
❑ Does this project make sense economically?
Drug

4. • “Drug resistance is the reduction in the effectiveness of a medication such as AMAs”
• Antimicrobial agents were viewed as miracle cures when first introduced into clinical practice
• After the discovery of penicillin, resistance develops and dims the luster of the miracle
• This serious development is ever present with each new antimicrobial agent
• Today, every major class of antibiotic is associated with the emergence of significant
resistance
Drug Resistance

5. Drug Resistance
Drug Resistance
Acquired Resistance
Natural Resistance
• Some microbes are inherently resistant to certain AMAs
• They lack the metabolic process or the target site which
is affected by the drugs
• E.g., Gram negative bacilli are unaffected by penicillin G
• Does not pose significant clinical problem
• Some microbes develop resistant strains due to use of
AMAs over period of time
• Some of these strains may even become resistant to
more than one antibiotic
• E.g., Staphylococci develop resistance to penicillin
• Pose significant clinical problems

6. • Mutation
• Gene transfer
Genetic Alteration
• Modification of target site
• Decreased accumulation
• Enzymatic inactivation
Altered expression
of protein
Mechanism of Drug Resistance

7. • Resistance developed by mutation is stable and heritable genetic changes that occur spontaneously and
randomly among microorganisms
• Mutation may occur in:
1) Plasmid 2) Target protein
3) Protein involved in drug transport 4) Protein important for drug activation or inactivation
• Mutation resistance may be single step or multistep
• Single step mutation may result in high degree of resistance
• Multistep gene may modify the more number of genes and decrease the sensitivity of AMAs to pathogens
Mechanism of Drug Resistance
(Genetic Alteration)
Mutation

8. • Resistance causing gene is transferred from one organism to other,
is called horizontal transfer of resistance. Rapid spread of
resistance can occur by this mechanism.
• Multidrug resistance can be acquired through this mechanism.
a) Transformation
b) Transduction
c) Conjugation
Mechanism of Drug Resistance
(Genetic Alteration)
Gene Transfer

9. • It will occur in natural conditions
• Bacteria taking up resistance carrying naked DNA from its
environment and incorporating it into its genome through normal
cross-over mechanism
• Become unresponsive to drug
Mechanism of Drug Resistance
(Gene Transfer)
Transformation

10. • It is the transfer of resistance carrying gene to another bacterium
through bacteriophage
• The “R” factor is taken up by the phage and delivered to another
bacterium which it infects
• Penicillin, erythromycin and chloramphenicol resistance have been
found to be phage mediated
Mechanism of Drug Resistance
(Gene Transfer)
Transduction

11. • Cell to cell contact; transfer of chromosomal and extrachromosomal DNA from one bacterium to another
through sex pili.
• Gene carrying the resistance or “R” factor is transferred only if another “resistant transfer factor (RTF) is
present.
• Conjugation may frequently occur in colon, here large variety of Gram-negative bacilli come in close
contact.
• Chloramphenicol resistance to typhoid bacilli and streptomycin resistance to E. coli and many others have
been traced to this mechanism.
Mechanism of Drug Resistance
(Gene Transfer)
Conjugation

12. • Alteration of an antibiotic’s target site through mutation can confer resistance
• For example, S. pneumoniae resistance to β-lactam antibiotics
Mechanism of Drug Resistance
(Altered Expression of Protein)
Modification of Target Sites

13. • Decreased uptake or increased efflux of an antibiotic can confer resistance
• Drug is unable to attain access to the site of its action
• For example, gram-negative organisms can limit the penetration of certain agents, including β-lactam
antibiotics
Mechanism of Drug Resistance
(Altered Expression of Protein)
Decreased Accumulation

14. • The ability to destroy or inactivate the antimicrobial agent can also confer resistance on microorganisms.
• Examples of antibiotic-inactivating enzymes include:
1. β-lactamases (“penicillinases”) that hydrolytically inactivate the β-lactam ring of penicillin,
cephalosporin, and related drugs
2. Acetyltransferases that transfer an acetyl group to the antibiotic, inactivating chloramphenicol or
aminoglycosides
Mechanism of Drug Resistance
(Altered Expression of Protein)
Enzymatic Inactivation

15. Genetic Determinants of Drug Resistance

16. • Resistance mediated by genetic change in bacteria
Genetic Determinants
of Drug Resistance
1. Chromosome-mediated resistance
2. Plasmid-mediated resistance
3. Transposons-mediated resistance
3 Types

17. • Occurs as a result of spontaneous mutation
• Mutation in the gene that codes for either:
1) the target of drug or 2) the transport system in the membrane of the cell wall
• Frequency of chromosomal mutation is much less (1 in 10 million cells)
Genetic Determinants
of Drug Resistance
Chromosome-mediated resistance

18. • “Plasmid is a small, circular, extrachromosomal DNA molecule which
can replicate independently”
• Plasmid-mediated drug resistance in bacteria occurs by transfer of plasmid
and genetic materials
• Plasmid carrying resistance gene (r gene) are referred to as R plasmid
• May carry one or even two or more resistant genes
Genetic Determinants
of Drug Resistance
Plasmid-mediated resistance

19. • “Transposons are repetitive DNA sequences that have the capability to move (transpose) from one
location to another in genome”.
• Transposons can transfer from a plasmid to other plasmids or from a DNA chromosome to plasmid and
vice versa that cause the transmission of antibiotic resistance genes in bacteria.
• Transposons are unable to replicate independently, some may replicate during the process of integration
resulting in a copy in both the donor and acceptor DNA molecules.
Genetic Determinants
of Drug Resistance
Transposons-mediated resistance

20. A. Two plasmids, A and B (transposons
brown)
B. Enzyme encoded by transposons form a
cointegrate, transposons replicates
C. Enzyme encoded by transposons resolve
the cointegrate
D. Both plasmids contain the transposons
Genetic Determinants
of Drug Resistance
Transposons-mediated resistance

21. • Loss of affinity of target biomolecule of the microorganism with particular AMAs
• E.g., penicillin resistance to pneumococcal strain (alteration of penicillin binding proteins)
Drug Tolerant

22. Multidrug Resistance

23. • “MDR is antimicrobial resistance shown by a species of microorganism to at least
one antimicrobial drug in three or more antimicrobial categories”
• Antimicrobial categories are classifications of antimicrobial agents based on their mode of action and
specific to targe organisms
• MDRO may include:
❑ Bacteria
❑ Viruses
❑ Parasites and others
Multidrug Resistance

24. • Mechanism involved in MDR are:
❑ Enzymatic degradation
❑ Mutation at binding site
❑ Decreased accumulation
❑ Efflux pump
Mechanism of MDR

25. • Common multidrug-resistant organisms are usually bacteria:
❑ Extended-spectrum β-lactamase (ESBLs) producing Gram-negative bacteria
❑ Klebsiella pneumoniae carbapenemase (KPC) producing Gram-negatives
❑ Methicillin-resistant Staphylococcus aureus (MRSA)
❑ Vancomycin-Resistant Enterococci (VRE)
❑ MDR-TB
Common MDROs

26. • MRSA stands for methicillin-resistant Staphylococcus aureus
• A type of bacteria that show resistant to several antibiotics:
❑ Methicillin
❑ Oxacillin
❑ Nafcillin
• Transmitted by direct and indirect contact
MRSA

27. • Most S. aureus skin infections, including MRSA, appear as a bump or infected area on the skin that
might be:
❑ Red
❑ Swollen
❑ Painful
❑ Warm to the touch
❑ Full of pus or other drainage
❑ Accompanied by a fever
MRSA

28. • Extended-spectrum beta-lactamases (ESBLs) are enzymes
that are produced by Gram-negative bacteria Enterobacteriaceae
• Inactivate β-lactam (penicillin) type antibiotics
• Resistance to β-lactams emerged several years ago and has
continued to rise ESBLs
ESBLs

29. • MDR-TB is caused by Mycobacterium
tuberculosis
• Resistant to both isoniazid and rifampin with or
without other anti-tb drugs
• Primary drug resistance
Infected with TB which is already drug resistance
• Secondary (acquired) drug resistance
Drug resistance develop during treatment
MDR-TB

30. Extensive Drug Resistance

31. • “XDR was defined as non-susceptibility to at least one agent in all but two or fewer antimicrobial
categories”
• Initially, the term XDR was created to describe extensively drug-resistant Mycobacterium tuberculosis
(XDR MTB) and was defined as ‘resistance to the first-line agents isoniazid and rifampicin, to a
fluoroquinolone and to at least one of the three-second-line parenteral drugs (i.e. amikacin, kanamycin
or capreomycin)’
XDR

32. • XDR-TB is caused by Mycobacterium tuberculosis
• MDR + resistance to fluoroquinolones + 2nd line
injectable anti-TB drugs (amikacin, kanamycin,
capreomycin)
XDR-TB

33. • “Pandrug resistance was defined as non-susceptibility to all agents in all antimicrobial categories”
PDR

34. • To limit the development of MDR & XDR, it has been suggested to:
❑ Use the appropriate antimicrobial for an infection; e.g. no antibiotics for viral infections
❑ Identify the causative organism whenever possible
❑ Select an antimicrobial which targets the specific organism, rather than relying on a broad-spectrum antimicrobial
❑ Complete an appropriate duration of antimicrobial treatment (not too short and not too long)
❑ Use the correct dose for eradication
❑ More thorough education of and by prescribers on their actions' implications globally
Preventive Measures

35. _________________________
Rapid Diagnostic Testing of Antimicrobial Resistance
Assignment

36. _________________________
THANK YOU!