This article describes types of plasmid, plasmid classification their role in antimicrobial resistance

1. Types of Plasmid, Classification and Their Role in AMR
There are different types of plasmid and they are classified into different categories on the
basis of size, function, genetic content, host range and replication mode.
What are Plasmids?
Plasmids are genetic elements found inside bacterial cell. These are small, circular piece of
DNA, an extrachromosomal genetic element, which replicate by their selves independent of
bacterial chromosomes. Plasmids contain different combinations of genes and serve diverse
functions like enabling bacteria to adapt according to different environmental conditions such
as high antibiotic, heavy metals and ions in environment.
They also contribute in evolution and spread through genetic diversity, and dissemination of
genes. Plasmids can be modified for different purposes like molecular biology research use
and they are often used to carry genes during genetic engineering
How Many Types of Plasmid are Found in Bacteria?
Plasmids can be classified on the basis of various characteristics, including their size,
replication mode, host range, function, and genetic content. Plasmids may vary greatly in
their characteristics and overlap multiple classifications which make the classification system

2. of plasmids flexible and dynamic.
Classification and types of plasmid
Here are some common classifications of plasmids:
Types of plasmid on the basis of size
1. Small plasmids: These plasmids size range from a few kilobases (kb) to tens of kilobases.
2. Medium plasmids: Their size generally ranges from tens to hundreds of kilobases in size.
3. Large plasmids: Size of large plasmids can be several hundred kilobases to a few megabases
in size.
Types of plasmid on the basis of replication mode
1. Rolling circle plasmids: These are plasmids which adopt rolling-circle mechanism during
replication and produce single-stranded DNA intermediates.
2. Theta (θ) replicating plasmids: These are plasmids which adopt theta structure mechanism
during replication and form a replication bubble.
3. Linear plasmids: These are plasmids which possess linear DNA molecules rather than circular
and replicate using different mechanisms.
Types of plasmid on the basis of host range
1. Narrow host range plasmids: These include plasmids which can be transferred and
maintained in specific bacterial specie and strains.
2. Broad host range plasmids: These include plasmids which can be transferred and
maintained in wide range of specific bacterial specie.
Types of plasmid on the basis of genetic content
1. Cloning vectors: These are types of plasmids designed for the cloning and replication of
foreign DNA fragments in host cells.
2. Expression vectors: These plasmids carry specific genetic elements to facilitate the
expression of genes in host cells.
3. Transposons: These are mobile genetic elements which are capable to move within and
between plasmids, chromosomes, and genomes.
Types of plasmid on the basis of function
On the basis function plasmids can be broadly classified into
1. Conjugative plasmids and
2. Non-conjugative plasmids
Conjugative Types of Plasmid
They carry a set of transfer genes which promote sexual conjugation among bacterial cells
and facilitate transfer of genes among bacteria. These include
1. F- plasmid (F factor )

3. 2. R plasmids or R factor
3. Col- plasmids
4. Heavy metal ion resistant plasmids
5. Plasmids of catabolic activity
6. Metabolic Plasmids
7. Virulence plasmids
8. Ti plasmid (Tumor-inducing plasmid)
Non-conjugative Types of Plasmid
These are types of plasmid which do not possess genes which encode machinery for
conjugation and carry set of genes which do not contribute in sexual conjugation among
bacterial cells and cannot transfer genes through conjugation.
They are commonly used in research and biotechnology applications. However, they cannot
mediate conjugation, they can be used as valuable tools for genetic manipulation and studies
of gene expression.
What are Inc/Rep Plasmids?
Inc/Rep plasmids are a diverse group of plasmids which contains specific replicon (rep) and
incompatibility (inc) regions.
• Rep (The replicon) region determines replication mechanism of the plasmid
• Inc (incompatibility region) ensures compatibility of plasmid or lack of interference with
other plasmids within same bacterial cell.
What are Stringent Plasmids?
Stringent plasmid is the type of plasmid that is dependent on chromosomal DNA and
replicate only when the chromosome replicates. They provide benefit to bacteria as they carry
proteins which are lethal to the bacterial cell.
What are Relaxed Plasmids?
Relaxed plasmids are the type of plasmid which is capable of replicating on their own and
they are not dependent on chromosomal DNA for replication.
What are Cryptic Plasmids?
Cryptic plasmids are small plasmids with no known phenotypic effect on bacterial cell
besides their replication functions and the role of genes carried by cryptic plasmids is unclear
so far. However, it is thought that small cryptic plasmids might have a major evolutionary
role due acting as moldable vectors to spread new genes through lateral gene transfers.
What are ColE2 Plasmid?
It is a non-conjugative variant of the ColE1 plasmid that lacks genes for but still contains few
antibiotic resistance genes and genes for other advantageous traits in bacterial cell.
What are pUC Plasmids?

4. These plasmids are non-conjugative plasmids but carry multiple useful features which
include origins of replication, antibiotic resistance markers, and cloning sites. They are
commonly used in molecular biology research as cloning vectors. It includes pUC series of
plasmids, such as pUC18 and pUC19
What are Shuttle Vectors?
These are non-conjugative plasmids also called shuttle vectors which have ability to replicate
in multiple host organisms, typically both bacteria and eukaryotic cells. Examples include
pBluescript and pBR322.
What are Expression Vectors?
These are non-conjugative plasmids also called expression vectors designed for the
expression of specific genes in host cells. They may carry promoters, transcription
termination sites, and other elements that facilitate gene expression.
What are Suicide Plasmids?
Suicide plasmids are non-conjugative plasmids typically carrying genes which induce cell
death during replication. They are used in molecular biology to introduce specific mutations
or gene deletions into bacterial genomes.