SUMMARY: R factors from Enterobacter strains isolated outside Japan were transferred to 2 and their resistance traits transduced by phage P 22. Of five factors conferring resistance to tetracycline (Tc), streptomycin (Sm), sulphonamides (Su) and chloramphenicol (Cm), three, one of which conferred also resistance to kanamycin (Km), behaved like previously reported factors in that: Tc was transduced by itself but never with any other trait; all other traits were usually co-transduced; no transductants could transmit resistance by conjugation, even after infection with F'-13 The other two factors, which conferred also resistance to benzylpenicillin (Pn), behaved similarly, except that: Pn was transduced only at a low rate, and was never co-transduced with any other trait; and a few transductants when given F'-13 became able to transmit. Four factors, two of type Tc, Sm, Su, Pn and two of type Tc, Su, Pn differed in that: nearly all Tc transductants acquired also all the other traits; Pn was usually co-transduced with the other traits; and some transductants could transmit by conjugation, even without F'-13 The various transductant classes obtained by treatment with P 22 grown on 2 carrying both an (Tc, Sm, Su, Cm, Km) and (Tc, Sm, Su, Pn) factor could be accounted for by transduction of fragments of either one or the other of these factors. The sorts of transductants produced by lysates of a strain possessing Tc, Sm, Su, Cm, Km determinants obtained by growing a strain carrying an (Tc, Sm, Su, Cm) factor with one carrying an (Km) factor suggested that the strain carried two factors, not a recombinant factor. Both and factors conferring resistance to benzylpenicillin conferred also resistance to cephalothin and cephaloridine and caused the constitutive production of a β-lactamase, active on both benzylpenicillin and on cephalothin. All four and one of the five factors resembled factors in that they protected strain 2 against the bactericidal effect of ultraviolet irradiation.


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