Transferable trimethoprim resistance in urinary tract pathogens isolated in Finland and Sweden.

The incidence of trimethoprim resistance (MIC greater than 4 micrograms/ml) among urinary pathogens from inpatients was earlier shown to be 1.6-3.6% in Stockholm and 31-49% in Turku in 1977-1978. In strains from this study trimethoprim resistance could be transferred from 13/51 donor strains. Resistance to streptomycin was co-transferred in all matings but 2, and to tetracycline, ampicillin, carbenicillin and chloramphenicol in some cases. Sulphonamide resistance was co-transferred in 2 cases. In all matings but 1 at least 1 plasmid was transferred. A plasmid with similar molecular weight was transferred from 5 Turku and 4 Stockholm donor strains. Restriction enzyme digestion of this plasmid DNA showed many common bands after electrophoresis. In DNA-DNA duplex studies, using 3H-labelled Col E 1::Tn 7 as the probe, the presence of Tn 7 DNA sequences was confirmed in the 5 donor strains from Turku and 1 from Stockholm. Electrophoresis of plasmid DNA with and without digestion with restriction enzymes together with DNA-hybridization were thus useful methods to investigate the presence of genetic determinants for trimethoprim resistance in 2 areas. Other determinants than transposon Tn 7 were also present.