Recombination Between a Thermosensitive Kanamycin Resistance Factor and a Nonthermosensitive Multiple-Drug Resistance Factor

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Abstract
The thermosensitive kanamycin (KM) resistance factor, R(KM) t , and a nonthermosensitive multiple-drug resistance factor, R 100 , were simultaneously introduced into Escherichia coli and Salmonella typhimurium . The temperature sensitivity of both R factors remained unchanged as long as they replicated independently. Under certain conditions, however, a new thermosensitive R factor harboring resistance markers for kanamycin, streptomycin (SM), and sulfanilamide (SA) was obtained by recombination between the R(KM) t and R 100 factors. R factors carrying resistance markers for KM and SA, or for SM and SA, were obtained from the recombinant R(KM SA SM) t by spontaneous segregation. Though the R 100 factor has been known as an fi + (positive for F-mediated fertility inhibition of its host) type and it does not restrict any coexisting phages, the thermosensitive recombinants of R 100 with R(KM) t and their segregants were found to be fi − and to restrict the replication of all T-even phages, as does the R(KM) t factor. Double infection immunity was not observed between the R(KM) t and R 100 factors.