ABSTRACT
The tetracycline resistance determinant tet(S) was first detected in antibiotic multiresistant Listeria monocytogenes BM4210 and subsequently in strains of Enterococcus faecalis. Transfer of tet(S) from clinical isolate E. faecalis BM4242 to E. faecalis strains JH2-2 and OG1RF was found to require the presence in the donor strain of the 55 kb conjugative plasmid pIP825. Comparison of restriction endonuclease generated maps of the donor, the two recipients, and of four transconjugants indicated that transfer of tet(S) (i) was from chromosome to chromosome, (ii) resulted in the acquisition of an approximately 40 kb element in the same chromosomal region and (iii) was associated with the exchange of large chromosomal fragments. Similar observations were made following conjugal transfer of tet(S) from four other E. faecalis clinical isolates.
Subject(s)
Chromosomes, Bacterial , Conjugation, Genetic , DNA, Bacterial/genetics , Enterococcus/genetics , Tetracycline Resistance/genetics , Chromosome Mapping , Plasmids/geneticsABSTRACT
Twenty-four clinical isolates of Staphylococcus aureus collected from various geographic areas and four reference strains were studied by (i) agar diffusion with disks impregnated with 5 microg oxacillin and reading after incubation at 30C for 24 hours, (ii) Southern hybridization with a probe specific for the mecA gene, and (iii) the BBLreg CrystalTM MRSA ID system. There was perfect correlation between the three methods: the BBLreg CrystalTM MRSA ID system detected methicillin resistance in the fifteen strains hybridizing with the mecA probe and classified as resistant by the oxacillin disk diffusion test; the thirteen remaining strains were susceptible by agar diffusion and by the BBLreg test and did not hybridize with the mecA probe. The BBLreg CrystalTM MRSA ID System, therefore, appears to be an accurate method for rapid detection of Staphylococcus aureus exhibiting homogeneous resistance to methicillin.
