What are the common types of plasmids?

There are a couple of different ways that plasmids can be classified. Based on function, there are five types of plasmids: 

• Resistance or R plasmid: Resistance plasmids carry the genes coded for antibiotic resistance in bacteria. These genes strengthen the bacterial cell’s defense against antibiotics, poisons, and other environmental factors. Resistance plasmids may also increase a bacterial strain’s resistance to antibiotics by transferring themselves through conjugation.  
• Fertility or F plasmid: Fertility plasmids carry transfer genes coded for fertility. They are also involved in the transfer of genetic material among bacteria through conjugation. 
• Virulence Plasmid: Virulence plasmids carry genes that code for bacteria to be pathogenic. When inside a bacterium, the virulence plasmid turns that bacterium into a pathogen, which is responsible for causing various diseases. 
• Col plasmid or Bacteriocins: Col plasmids produce colicins or bacteriocins, which are proteins that defend the host bacterium by killing the other harmful bacterial strains.  
• Degradative Plasmids: Degradative plasmids have genes that code for special enzymes that degrade specific compounds. This type of plasmid enables the host bacterium to digest compounds such as toluene, camphor, salicylic acid, and xylene, which are not commonly found in nature.  

Plasmids may also be classified as conjugative or non-conjugative. Reproduction in bacteria takes place by sexual conjugation, which involves the genetic material getting transferred from one bacterial cell to another. Plasmids that carry transfer genes that initiate the process of conjugation are called conjugative plasmids. Plasmids that do not contain the transfer gene and are unable to initiate the conjugation process are called non-conjugative plasmids. These plasmids need the help of conjugative plasmids in order to be transferred through sexual conjugation.