Bacteria can become resistant to antibiotics through several mechanisms, including modification of antibiotic molecules, modification of antibiotic targets, and alterations in bacterial genomes. Resistance genes can spread between bacteria through conjugative plasmids and transposons. Conjugative plasmids contain the machinery for transfer between bacterial cells through conjugation. Transposons are DNA segments that can move within genomes. Composite transposons contain resistance genes flanked by insertion sequences that allow the resistance genes to spread. Conjugative transposons not only transpose but also direct their own transfer between cells. Lateral gene transfer through these mobile genetic elements is a major cause of the rise and spread of antibiotic resistance in bacterial populations.

1. Conjugation,
Transposition and
Antibiotic Resistance
Presented To: Dr. Ambreen Ahmad
Presented By: Atika Noor
Roll No: M.Phil-01
Mphil Botany 1st Semester

2. CONTENTS:
Introduction
Infections due to Antibiotic Resistance
History of Antibiotic Era
Mechanisms Of Antibiotic Action
Types and origin of antibiotic resistance
Spread of resistance
Mechanisms for DNA Transfer
• Plasmids
• Replication of plasmids
 Conjugative plasmids
 The conjugation pathway
 Insertion elements
 Transposase proteins
 Composite Transposable
Elements
 Conjugative Transposons
 Microbial Ecology And
Antibiotic Resistance
 Conclusion
2

3. 3Antibiotic Resistance:
Why do bacteria become resistant to
antibiotics?
When antibiotics are used to kill the bacterial
microorganisms, a few microorganisms are able to
still survive, because microbes are always mutating,
eventually leading to a mutation protecting itself
against the antibiotic.
 Antibiotic resistance occurs when an
antibiotic has lost its ability to effectively
control or kill bacterial growth; in other
words, the bacteria are "resistant" and
continue to multiply in the presence of
therapeutic levels of an antibiotic.

4.  By the discovery of first antibiotic, penicillin, in the early 20th
century, it was considered as it helped to protect humans and
their domesticated animals from bacterial agents.
 Many alleged that this finding would lead to elimination of all
illnesses and form a society of perfect health.
 Though, none of these expectations were true and slowly the
miracle medicine penicillin became less effective.
Introduction:
4

5. ANTIBIOTIC RESISTANCE INFECTIONS:
• Staphylococcus aureus was initially treated with penicillin,
• later on only 10% strains remain sensitive.
• Has been treated with a 2nd generation penicillin as methicillin.
• However, 30 -40% strains are now resistant to methicillin as well.
• Such strains are known as MRSAs, for methicillin-resistant
Staphylococcus aureus.
• Only antibiotic left for the treatment of these MRSA strain is Vancomycin,
• but due to excessive use of Vancomycin, resistance also spread for this
antibiotic.
• In 1999, first case for Vancomycin MRSA resistance was reported.
• Mycobesterium tuberculosis, is also one of those pathogenic strains-
approaching a state with No effect of antibiotics
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6. HISTORY OF ANTIBIOTIC ERA
• In 19th century more than half of surgical patients had developed
infections
• A consequence of critical studies antiseptic treatments used during
surgeries reduce the rate of infection.
• The beginning of the modern “antibiotic era” is associated with the
names of Paul Ehrlich and Alexander Fleming.
• Ehrlich - “magic bullet”
• Alexander Fleming- penicillin
Along these following also helped in era of antibiotics
Sulfa drugs by Gerhard Domagk
Streptomycin by Selman Waksman
First antibiotic resistant mutants of Pneumococcus in 1951 by Ronald
Hotchkiss
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7. 7
Types and Origin of Antibiotic Resistance:

8. TYPES AND ORIGIN OF
ANTIBIOTIC RESISTANCE:
There are three most important mechanisms
which are responsible for antibiotic resistance
Modificaion in the antibiotic molecule.
Modification of target of antibiotics.
Alterations in the bacterial genome.
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9. 9
Modification in the antibiotic molecule:
Examples:
 Methyl group is added by the victim bacteria to the
erythromycin to make it inactive and thus the bacteria become
resistant for the erthromycine.
 β-lactamase genes is activated which converse resistance against
β-lactam antibiotics and penicillin, by activating an enzyme that
would cleave β-lactam ring.

10. 10
 Modification of the target agent
of the antibiotics:
 In Vencomycine resistant, D-alanine-D-
alanine cross linkages in the cell walls with
the D-alanine-D-lactate linkages thus there
would be no connection site for
vancomycine.
 Controlled by van cluster of genes
specifying the D-alanine-D-lactate
synthesis.

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Other examples:

12. Alterations in the bacterial genome:
 Modification into the Transporting Membrane or
Entering Channels by modifying porin proteins.
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13. Spread of Resistance Genes:
 Changes in base pair substitution by mutations in gene
encoding the antibiotic target are sufficient to confer
resistance.
 Sensitive bacterium acquires new DNA sequence by
lateral transfer from another organism
 Two mechanisms operate together. E.g. In Penicillin-
binding proteins
___De novo mutation in PBPs or
___Changes by lateral DNA transfer.
13

14. 14
Spread of Antibiotic
Resistance:
By Conjugative Plasmids
By Tranpositions:

15. CONJUGATIVE PLASMIDS:
Along with sequences for replication, some plasmids also contain machinery
for transfer between cells via conjugation. These plasmids are also called self-
transmissable plasmids. For example F plasmid of E. coli
The conjugation pathway
Two bacteria come close together by formation of pilus
F DNA then transferred from F+ to F- strain through the mating pore.
F+ do not lose their copies of F plasmid.
DNA transfer can begins from a specific sequence on the donor F plasmid,
named ori T
Nicking reaction is carried out by an enzyme called “Relaxase”,
which together with other proteins forms the relaxosome complex
relaxase-bound DNA end is then unpaired from complementary DNA strand
and transferred to the recipient cell.
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16. 16
Conjugative Plasmids

17. 17
 General Mechanism of Spread of Resistance
By Conjugative Plasmids:

18. 18

Transposons & Integrons
Resistance genes are often associated with transposons, genes that
easily move from one place to another within the genome.
Many bacteria also possess integrons, pieces of DNA that accumulate
new genes.
Gradually a strain of a bacterium can build up a whole range of
resistance genes.
This is multiple resistance.
These may then be passed on in a group to other strains or other
species.

19. INSERTION ELEMENTS:
The DNA segments that move are called transposons or transposable
elements.
Genetic transposition is one of the most active mechanism of
rearrangement of DNA
Transposition involves DNA replication (replicative transposition)
All autonomously active IS elements encodes at least one protein,
called a transposase, that carries out the initial DNA breaking and
joining reactions that mediate transposition.
Each transposon DNA encodes sites that specifically recognized and
bound by transposase near the DNA ends, thereby positioning the
transposase for the chemical steps of the transposition reaction.
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20. 20

21. Two closely related IS elements located in the DNA may form a composite
transposon, or Tn elements.
 Tn elements contain four transposon ends that can potentially serve as
binding sites for transposases
In those cases where two outside ends are recruited by transposase
protein, the entire DNA unit between two can then transpose carrying along
the DNA In between.
 Tn5 is an example of two IS50 elements flanking genes resistance to
kanamycin, bleomycin, and streptomycin.
Composite Transposable Elements
21

22. Fig: Composite Transposable Elements
22

23. CONJUGATIVE TRANSPOSONS
• Some transposons are not only transposons but they actually direct their
own conjugative transfer.
• Clinically, “the conjugative transposons are a major contributor to failed
antibiotic treatments of gram positive bacterial infection”.
• It is also possible for conjugative transposons to transpose to another
location with in the a single cell.
• One well studied example is Tn916. The transposition/ conjugation cycle
which is as following:
• Once the single stranded DNA copy is transferred to recipient cell , it is
copied by host cell enzymes to generate fully duplex transposon circle
staggered
cleavage at
each end of
element
DNA
Circul
arized
protruding
ends
generated
by
staggered
cleavage
close
region of
non-base-
paired
DNA
(heterodup
lex) form
Nicking at internal
element oriT site for
conjugation to be
carried out
Transfer of
sequence from
heteroduplex
overlap region
23

24. Fig: Transposon Element Transfer.
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25. 25
By Tranpositions:
 Replicative Transposons are used to
spread antibiotic Resistance.
• Step 1: Integration of transposon into Plasmid.

26. 26
Spread 2: Replication Of Transposons And
Transferring To The Other Place In The
Genome.

27. CONCLUSION:
Lateral DNA transfer is the major cause of antibiotic resistance in bacteria.
Mobile DNA is a major cause of resistance.
Lateral DNA transfer systems are most active and it seems inevitable that
these resistance genes will appear quickly in medically important
pathogens in response to treatment.
The major threat of losing effective antibiotic treatments permits much
more thoughtful arrangement of antibiotic use, incorporating a realistic
review of high frequency of lateral transfer.
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28. References:
 B. Karsten, S. Robin, E.B. Julie, C. D. Hotopp (2017), Lateral gene transfer
between prokaryotes and eukaryotes, Experimental Cell Research, Volume 358,
Issue 2, Pages 421-426.
 Burrus V, Pavlovic G, Decaris B, Guedon G. 2002. Conjugative transposons: the
of the iceberg. Mol Microbiol. 46: 601-610.
 F. A. Kondrasho, (2002), Misunderstanding the consequences of lateral DNA
transfer, cell press, Volume 18, Issue 8, Pages 431-432.
 H.P. Schweizer (2008) Bacterial genetics: Past achievements, present state of the
field, and future challenges Biotechniques, 44, pp. 633-641
 M. Qiao, G. Ying, A. C. Singer, Y. Zhu, January 2018, Review of antibiotic
resistance in China and its environment, Environment International, Volume 110,
Pages 160-172.
 M. S. Morehead, Scarbrough C. September 2018, Emergence of Global Antibiotic
Resistance Primary Care: Clinics in Office Practice, Volume 45, Issue 3, Pages
484.
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 Salyers AA, Shoemaker NB, Stevens AM, Li LY. 1995. Conjugative transposons: an
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