1986 Volume 17 Issue 4 Pages 531-537
Bacteroides fragilis KHM027, which is resistant to penicillins, cephalosporins and oxyiminocephalosporins was examined for the presence of β-lactam antibiotics resistance plasmid. Plasmid DNA isolated by Kado's DNA extraction method was analyzed by agarose gel electrophoresis. This strain was found to harbor four different sizes of plasmid DNA. Two different sizes of the β-lactam antibiotics resistance plasmid were isolated by genetic transformation of Escherichia coli K-12 strain HB101. These plasmids were designated as pBFSK1 and pBFSK2. The molecular sizes of these were 2.6kb for pBFSK1 and 5.8kb for pBFSK2. Genetic and physical analyses were used to characterize the pBFSK1. The major objectives of this study on molecular genetics were to : (1) construct a physical map of the plasmid by restriction endonuclease cleavage studies, (2) map the bla gene region by insertion mutation method, and (3) observe the stability of plasmid in four different E. coli K-12 strains (HB101, JC1569, λ984, C600). Results from restriction endonuclease digestion by a combination of standard approaches, each one site of PstI, EcoRI recognition sequence and two sites of DraI, PvuII recognition sequence were mapped on the pBFSK1 molecule. The putative bla gene region was mapped over the PstI site by insertion mutation of β-lactam antibiotics resistance phenotype. 50 single colonies from each E. coli strain transformed by pBFSK1, were analysed to observe the stability of plasmid. This plasmid pBFSK1 was harbored extremely stable in each E. coli cells. Resistance pattern of each transformants suggests that the bla gene of pBFSK1 is an oxyiminocephalosporinase (CXase) form. Usually, the CXase gene is encoded on chromosome DNAs. It is very interesting that the CXase gene is encoded on the plasmid pBFSK1.
