title: Covert fi- R factors in fi+ R+ strains of bacteria.
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.
mesh_terms: D003087:Colicins / Q000096:biosynthesis; D003090:Coliphages; D003227:Conjugation, Genetic; D004352:Drug Resistance, Microbial; D004926:Escherichia coli; D005111:Extrachromosomal Inheritance; D005827:Genetics, Microbial; D012641:Selection, Genetic; D014161:Transduction, Genetic
chemical_list: D003087:Colicins