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J Bacteriol. 1969 February; 97(2): 780-786
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Covert fi^– R Factors in fi^– R⁺ Strains of Bacteria

^a Medical Research Council Microbial Genetics Research Unit, Hammersmith Hospital, London W12
^b Department of Microbiology, Lister Institute of Preventive Medicine, London SW1, England

ABSTRACT

The presence of an fi^– sex factor can be detected by propagation of the I-specific phage If1. By use of this method of detection, a high proportion of strains with fi⁺ R factors were shown also to carry an fi^– factor which was frequently a second R factor. In some doubly R⁺ strains, the fi⁺ and the fi^– factor were observed to be transferred independently at conjugation.

¹ Present address: Istituto di Microbiologia, Università di Pavia, Pavia, Italy.