[Trimethoprim resistance plasmids: transferability and incompatibility groups (author's transl)].

Over a three year period, 119 strains of enterobacteria isolated from patients have been found resistant to trimethoprim (TMP) and sulfonamides (Su); 11 strains were resistant to TMP only. MIC of TMP were between 32 and 2048 microng/ml. Three groups of strains are described: (1) thymineless variants (2 strains); (2) TMP resistance non-transferable into Escherichia coli K12 (95 strains); (3) TMP resistance transferable into E. coli K12 (33 strains). TMP marker and Su marker have been transferred independantly from 13 strains; they were cotransferred from 20 strains. The incompatibility group of 31 plasmids has been determined: 10 belong to the fi+ type, group FII; 21 belong to the fi--type, group 6, group 7, group 10, group N and group I1. Epidemiological implications of such a wide range of incompatibility groups among a small number of plasmids specifying TMP resistance are discussed.