The Evolution of R Factor

Although the therapeutic use of antibiotics favors the selection of bacteria that contain R factor, it does not necessarily follow that man-made antibiotics have induced the evolution of R factor. We have obtained evidence that R factor evolved before the advent of the antibiotic era. Cultures of fecal flora were taken from 128 people living in an "antibiotic-virgin" community in north Borneo. The total experience of this entire community with antibiotics consisted of 19 injections of penicillin given in 1959 during a yaws-eradication program. Six strains of Escherichia coli isolated from four subjects were found to possess transferable drug resistance. This multiple-antibiotic resistance was shown to be due to R factor by serial transfer through several recipients, by the absence of transfer from cell-free filtrates, and by the occurrence of transfer independently of the chromosome.