b) Resistance factor or R-factor.(RF)

The R- factor are extra extra chromosomal  genes which carry information of resistance against variety of antibiotics. It gets transferred to the receipient along with sex factor. These genes get transferred rapidly to the antibiotic sensitive cells by conjugation. These genes get transferred between bacteria like E.coli ,Salmonella typhi and Shigella dysentriae. It has been observed to increase resistance against four iwdesly used antibiotics like sulphanilamide, streptomycin, chloramphenicol and tetracycline.