Appearance of a new trimethoprim resistance gene, dhfrIX, in Escherichia coli from swine.
A new gene, dhfrIX, coding for a trimethoprim-resistant dihydrofolate reductase (DHFR), was found in porcine isolates of Escherichia coli. The new enzyme, DHFR IX, containing 178 amino acids, showed an amino acid similarity of about 26% with DHFR I and the chromosomal DHFR of E. coli K-12. The dhfrIX gene was observed to occur on two distinctly different transferable plasmids, although a fragment of about 2.9 kb, including dhfrIX, had an identical restriction enzyme digestion map in each case. The new plasmid-borne dhfrIX gene mediates resistance to a drug level of only about 250 micrograms/ml, as compared with more than 1,000 micrograms/ml for the more frequently encountered dhfrI gene. The new plasmid-borne trimethoprim resistance gene could have been selected and spread as a consequence of the extensive use of trimethoprim in veterinary practice in Sweden. It will be important to try to follow its possible occurrence in human pathogens as well.
Jansson
C
C
Department of Pharmaceutical Microbiology, Uppsala University, Sweden.
Sköld
O
O
D000595:Amino Acid Sequence; D000818:Animals; D004262:DNA Restriction Enzymes / Q000187:drug effects / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D005493:Folic Acid Antagonists; D005798:Genes, Bacterial; D006824:Hybridization, Genetic; D008969:Molecular Sequence Data; D010957:Plasmids / Q000187:drug effects / Q000235:genetics; D013552:Swine; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics; D014295:Trimethoprim / Q000494:pharmacology; D014296:Trimethoprim Resistance / Q000235:genetics*
D005493:Folic Acid Antagonists; D014295:Trimethoprim; D013762:Tetrahydrofolate Dehydrogenase; D004262:DNA Restriction Enzymes