Drug Resistance of Enteric Bacteria

A nontransferable R21 (TC) factor was obtained by transduction of R10 (TC.CM.SM.SA) with phage epsilon in group E Salmonella. The R21 (TC) factor acquired transmissibility by the normal conjugal process when group E Salmonella strains harboring R21 (TC) factor were infected with wild‐type F or R16 (CM) factor. This transmissibility at high frequency was accounted for by the formation of the recombinant F TC and R10 (CM) TC factors. The F TC and R16 (CM) TC factors were genetically the same as the original F and R16 (CM) factors, except for the ability to confer TC resistance. In the transduction of F TC factor with phage P1, a dF TC (d: defective) factor was obtained that was defective in many F properties, such as the ability to introduce host chromosome and produce male substance, but was capable of transducing TC resistance (dF TC‐infection) at low frequency.