title: The type VII dihydrofolate reductase: a novel plasmid-encoded trimethoprim-resistant enzyme from gram-negative bacteria isolated in Britain.
abstract: Plasmid pUN835 was identified in an Escherichia coli strain isolated from an outbreak of porcine diarrhoea on a farm near Nottingham, UK. The trimethoprim resistance gene did not hybridize with any of the gene probes derived from known plasmid-encoded trimethoprim resistance genes. The trimethoprim resistance gene of pUN835 was shown to encode the production of a dihydrofolate reductase which confers high-level resistance on its host. This enzyme was smaller than most plasmid-encoded dihydrofolate reductases (molecular mass = 11,500) and was labile to heat. It had relatively low affinity for the substrate dihydrofolate (Km = 20 microM) and it was resistant to competitive inhibition by trimethoprim (Ki = 7.0 microM). We classify this novel enzyme as type VII.
authors.affiliation: Department of Bacteriology, Medical School, University of Edinburgh, UK.
authors.forename: S G
authors.initials: SG
authors.lastname: Amyes
authors.forename: K J
authors.initials: KJ
authors.lastname: Towner
authors.forename: G I
authors.initials: GI
authors.lastname: Carter
authors.forename: C J
authors.initials: CJ
authors.lastname: Thomson
authors.forename: H K
authors.initials: HK
authors.lastname: Young
mesh_terms: D000818:Animals; D015342:DNA Probes; D003967:Diarrhea / Q000201:enzymology / Q000382:microbiology / Q000662:veterinary; D004926:Escherichia coli / Q000235:genetics* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000201:enzymology / Q000382:microbiology / Q000662:veterinary; D007525:Isoelectric Focusing; D009693:Nucleic Acid Hybridization; D011815:R Factors; D013552:Swine; D013553:Swine Diseases / Q000201:enzymology / Q000382:microbiology; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000302:isolation & purification; D014296:Trimethoprim Resistance / Q000235:genetics*
chemical_list: D015342:DNA Probes; D013762:Tetrahydrofolate Dehydrogenase