Drug resistance transmitting factor present in bacteria is:

Drug resistance: It refers to unresponsiveness of a microorganism to an AMA, and is akin to the phenomenon of tolerance seen in higher organisms. Resistance may be developed by mutation or gene transfer: Gene transfer (infectious resistance) from one organism to another can occur by: 1.Conjugation: Sexual contact through the formation of a bridge or sex pilus is common among gram-negative bacilli of the same or another species. This may involve chromosomal or extrachromosomal (plasmid) DNA. The gene carrying the &;resistance&; or &;R&; factor is transferred onlv if another &;resistance transfer factor&; (F) is also present. Conjugation frequently occurs in the colon where large variety of gram-negative bacilli come in close contact. Even nonpathogenic organisms may transfer R factor to pathogenic organisms, which may become widespread by contamination of food or water. 2.Transduction: It is the transfer of gene carrying resistance through the agency of a bacteriophage. The R factor is taken up by the phage and delivered to another bacterium which it infects. 3.Transformation :A resistant bacterium may release the resistance carrying DNA into the medium and this may be imbibed by another sensitive organism-becoming unresponsive to the drug. This mechanism is probably not clinically significant except isolated instances of pneumococcal resistance to penicillin G due to altered penicillin binding protein, and some other cases. Resistance once acquired by any of theabove mechanisms becomes prevalent due to the selection pressure of a widely used AMA, i.e. presence of che AMA provides oppounity for the resistant subpopulation to thrive in preference to the sensitive population ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:670,671