STUDIES ON TRANSFERABLE DRUG RESISTANCE IN BACTERIA

IV. SUPPRESSION OF PLAQUE FORMATION OF PHAGES BY THE RESISTANCE FACTOR

Abstract

A phenomenon of suppressing plaque formations (abbreviated as spp.) of phages λ and Plkc by some R factors, which were used to infect the host cells of these phages, was described. In this respect, the R factors were divided into two groups; one has the character (spp (+)) and other has not (spp (-)). All of the spp (+) R factors tested were confirmed to be ri^-, that is, not to be endowed with the character of recombination interference. All of the ri⁺ R factors were spp (-). One case of ri- and spp (-) R factor was found. No difference could be observed between the adsorption rate of phage λto the resistantized cells carrying spp (+) R factor and those to the sensitive cells or to the resistantized cells carrying the spp (-) R factor. The phage λ (281), which was prepared by growing the original phage λ on the resistantized strain carrying the spp (+) R factor, was not suppressed by the spp (+) R factor. The insusceptibility of phage λ (281) was, however, not hereditary, and it became susceptible to the suppressive effect of the spp (+) R factor when it was again propagated on the sensitive strain. The change belongs, therefore, to the"host induced modification" or "host controlled variation" Thus, the spp (+) R factor, by which the host cells of phages are infected, changes the process of phage multiplication to decrease the number of plaques formed on one hand and for the progeny phages to be modified in their host specificity similarly to"host induced modification" or "host controlled variation" on the other. Some possible mechanism of the phenomenon of spp. and the modification, induced by the spp (+) R factor, were discussed.