[Epidemiology of resistance factors to antibiotics]

Resistance factors are small independent extrachromosomal DNA molecules (plasmids) conferring resistance on one or more antibiotics to the bacteria which harbour them; in Enterobacteriaceae and other gramnegative bacteria they are transferable by conjugation. The work is reviewed which has been undertaken to underline the importance of the R factors in nature, and more precisely in the current environment of the intestinal bacteria (animal and human gut, sewage) under the selective pressure of antibiotics or otherwise.