The chromosomal integration of a β-lactamase gene derived from the P-type R-factor RP1 inEscherichia coli

Abstract

The R-factor RP1, which carried the markersamp neo tet, confers resistance to penicillins by specifying the synthesis of Type IIIa β-lactamase. It was detected initially in a strain ofPseudomonas aeruginosa(Sykes & Richmond, 1970) and fragments spontaneously inPs. aeruginosastrain Ps 18 to give clones which carry only theampmarker. Such clones are said to carry the element RP 1–1 since they are still capable of specifying the transfer of ampicillin and carbenicillin resistance to appropriate recipients in mating experiments. However, unlike lines carrying RP 1, they contain no detectable extrachromosomal DNA (Ingramet al.1972), and the likely supposition is that theampgene in these clones has become integrated into the bacterial chromosome together with the regions necessary to allow such strains to act asampgene donors in mating experiments. It is probably cells ofPs. aeruginosain which theampgene has become integrated together with an RTF region that are responsible for the transfer of chromosomal markers reported by Holloway & Stanisich (1971).