Thermosensitive replication of a kanamycin resistance factor.

A strain of Proteus vulgaris isolated from the urinary tract of a patient with postoperative pyelonephritis and resistant to sulfonamide, streptomycin, tetracycline, and kanamycin (KM) was found to transfer only KM resistance by cell-to-cell conjugation. The genetic determinant controlling the transferable KM resistance was considered to be an R factor and was designated R (KM). Successive transfer of KM resistance was demonstrated also from Escherichia coli 20S0, which received the R (KM) factor, to other substrains of E.