R-factor Gene Expression in Gram-negative Bacteria

SUMMARY: Methods by which the R-factor 1818 was transferred from Escherichia coli K12 to different species of Gram-negative bacteria are described. Possession of 1818 resulted in the production of similar amounts of R-factor specific penicillinase per organism in E. coli, Serratia marcescens, Alkalescens sp. and Aerobacter aerogenes. The Aerobacter strain produced additionally a ‘chromosomal’ penicillinase which had no influence on the level of R-factor enzyme.

Two different strains of Proteus mirabilis containing R-factor 1818 produced only about 1/20th of this penicillinase activity per bacterium Two further R-factors 7268 and TEM also specifying penicillinase were introduced into the P. mirabilis strains and enzyme activities per bacterium of about 1/20th and 1/100th, respectively, were obtained compared with those in E. coli. All organisms in cultures of P. mirabilis exhibited properties of R-factor possession and thus R-factor instability cannot explain these results. It would seem that the phenotypic expression of R-factor penicillinase genes is impaired in this species.