Covert fi− R Factors in fi− R+ Strains of Bacteria

摘要

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.