又称抗药性因子.与抗化学药剂（主要是抗生素类）有关的一类质粒.它携带一种或几种抗药基因.存在不同Ｒ因子的细菌可具有抗氯霉素、链霉素、四环素和磺胺类药物等多种抗性.由承担抗药性转移功能的抗性转移因子和含有抗药基因、能赋予宿主菌以抗药特性的抗性决定因子组成.以上两种因子可独立存在，也可结合在一起.只有抗性决定因子而无转移因子的Ｒ因子，不能以接合方式转移.Ｒ因子使细菌具有多种抗药性的原因，主要是：（１）Ｒ因子编码的钝化酶使化学药剂的化学结构发生变化，使之失效.（２）控制了菌细胞膜的通透性，使药物不能进入细胞内.（３）阻止药物与细胞内的作用部位结合.Ｒ因子常以接合或转导方式在同一种属或不同种属的细菌中广泛传递，使耐药菌株不断增多，常给临床治疗带来很大困难.GOOGLE英文翻译:Also known as the resistance factor. And anti-chemical agents (mainly antibiotics) of a class of plasmids. It carries one or several resistance genes. There are different R factors in bacteria resistant to chloramphenicol, streptomycin , tetracycline and sulfa drugs and other resistance. by a commitment to drug resistance transfer factor resistance transfer of functions and products containing resistant genes, will provide the host bacteria resistant to drug-resistant properties of the composition of the decision factors. These two factors may independent existence, but also together. only without the transfer factor resistance determinants of R factors can not be otherwise transfer bonding. R factor to make bacteria resistant to a variety of reasons, mainly: (1) R factor encoded passivation enzyme so that the chemical structure of chemicals to change to make it ineffective. (2) control of the bacterial cell membrane permeability, so that drugs can not enter the cells. (3) to prevent drugs and the role of intracellular binding site. R factor often means bonding or transduction in the same or different species of a genus of bacteria in the wide range of transmission of drug-resistant strains growing, and often caused great difficulties for clinical treatment.