EPISOME-MEDIATED TRANSFER OF DRUG RESISTANCE IN ENTEROBACTERIACEAE. VII. TWO TYPES OF NATURALLY OCCURRING R FACTORS.

Watanabe, Tsutomu (Keio University, Tokyo, Japan), Hiroshi Nishida, Chizuko Ogata, Toshihiko Arai, and Sachiko Sato. Episome-mediated transfer of drug resistance in Enterobacteriaceae. VII. Two types of naturally occurring R factors. J. Bacteriol. 88:716-726. 1964.-Naturally occurring R factors are classified into two types, fi(+) and fi(-), depending on their fi characters. The term fi is an abbreviation of fertility inhibition and fi(-) and fi(-) mean, respectively, the presence and absence of suppression of the functions of the sex factor F of Escherichia coli K-12. It was found that fi(-) R factors reduce the efficiency of plating of phages lambda and T(1) in K-12; fi(+) R factors did not have this inhibitory action. One of the fi(-) R factors reduced the efficiency of plating of phage T(7) as well. Phages lambda and T(1) underwent host-induced modifications in the host carrying some fi(-) R factors. At least two types of fi(-) R factors were recognized by the types of their restriction and host-induced modification of these phages. CaCl(2) exhibited antagonistic actions against the restrictions of phages lambda and T(1) by fi(-) R factors. Transduction of the ability to ferment galactose with HFT lysates of lambda was reduced by fi(-) R factors. Ultraviolet induction of lambda was not affected by any R factors. Furthermore, adsorption of phages lambda and T(1) was not altered by the presence of any R factors. From these results, we concluded that the suppression of progeny formation of these phages by fi(-) R factors is due to some step(s) after adsorption of the phages to the bacteria. Superinfection immunity and mutual exclusion were found between two different fi(+) R factors but not between fi(+) and fi(-) R factors. The two different fi(-) R factors were frequently genetically recombined. but fi(+) and fi(-) R factors were not genetically recombined, as indicated by findings of independent transfer of these R factors by conjugation and by transduction from the donors having these two R factors. It was assumed from these findings that fi(+) and fi(-) R factors are considerably different episomes having different resistance-transfer factors.