Presence and dissemination of the multiresistance gene cfr in Gram-positive and Gram-negative bacteria

The emergence of the multiresistance gene cfr in staphylococci is of global concern. In addition to conferring resistance to phenicols, lincosamides, pleuromutilins, streptogramin A antibiotics and selected 16-membered macrolides, the cfr gene also confers resistance to the oxazolidinone linezolid. Linezolid is a last-resort antimicrobial agent for the treatment of serious infections in humans caused by resistant Gram-positive bacteria. The cfr gene is often located on plasmids and several cfr-carrying plasmids have been described, which differ in their structure, their size and the presence of additional resistance genes. These plasmids are important vehicles that promote the spread of the cfr gene not only among bacteria of the same species, but also among those of different species and genera. Moreover, the cfr gene has been identified in close proximity to different insertion sequences, which most probably also play an important role in its dissemination. This review summarizes current knowledge on the genetic environment of the multiresistance gene cfr with particular reference to mobile genetic elements and co-located resistance genes that may support its emergence.