Abstract
Two hundred and eighty-seven coliform bacteria were isolated from 116 rectal swabs or faecal specimens obtained from 113 patients. By means of plasmid analysis and resistance transfer (R-transfer) Escherichia coli was found to differ from other enteric genera in plasmid distribution. Criteria were proposed that enabled in-vivo "R-transfer potential" and in-vivo "R-transfer rate" to be calculated. From each of 22 of the 113 patients numerous coliforms were isolated, of which at least one per patient contained one or more self-transmissible R-plasmids potentially transferable to 43 other coliforms. Evidence indicated that R-plasmid transfer had occurred in vivo on two of the 43 potential occasions. These results are discussed in the context of plasmid ecology in the human host.