RNA from Salmonella typhimurium hybridizable with R-factor DNA

Abstract

MULTIPLE antibiotic resistance was first encountered in Shigella strains isolated in Japan in 1955. Similar multiple resistant Enterobacteria are now so widespread that the mechanism of their resistance is of considerable interest¹. In these bacteria the determinants of resistance are carried on an extrachromosomal element, or plasmid, known as a resistance (R) factor, which is composed of DNA of a characteristic base composition². Evidence suggests that bacteria harbouring R-factors produce antibiotic-inactivating enzymes, and this may be the basis of their multiple resistance. Thus β-lactamases active against penicillins³ and cephalosporins⁴, chloramphenicol acetylase^5,6 and streptomycin adenylate synthetase⁷ have been described in R-factor strains. If an R-factor carries the structural genes for these enzymes, then, according to the theory of protein biosynthesis, resistant bacteria should contain some messenger RNA of complementary base sequence to the R-factor DNA. We here describe the detection of an RNA species present in Salmonella typhimurium harbouring an R-factor, hybridizable with, and thus complementary to, DNA of the R-factor.