Nature 220, 1046 - 1047 (07 December 1968); doi:10.1038/2201046b0

Incidence of R Factors among Gram Negative Bacteria in Drug-free Human and Animal Communities

I. J. MARÉ

Department of Microbiology, University of Pretoria, South Africa.

TRANSFER of drug resistance among Enterobacteriaceae is mediated by cytoplasmic particles called R factors which seem to consist of a transfer factor (RTF) coupled to genes which determine the drug resisting capacity of the bacterial host². Although the origin of the intact R factor is obscure³, there is some evidence⁴ that the transfer factors are widely distributed in the Enterobacteriaceae, and that they may on some occasions have picked up bacterial chromosome genes which determined drug resistance. Another possibility¹ is that R factors arose in otherwise unrecognized plasmids during the course of mutations to a resistant form, but whatever mechanism is responsible, there is no doubt that R factors are selected and maintained by drugs in the environment⁴. The finding⁵ of transmissible drug resistance in a strain of Escherichia coli lyophilized in 1946 may indicate that R factors were already present in pre-antibiotic cultures. The purpose of this investigation was to determine the incidence of R factors in intestinal Gram-negative bacteria of wild animals and humans living in surroundings free of drugs.

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