R-factor Mediated Dihydrofolate Reductases which Confer Trimethoprim Resistance

R-factor mediated trimethoprim resistance: result of two three-month clinical surveys.

All urinary tract isolates were monitored in the Whittington Hospital, London for trimethoprim resistance over a three-month period in 1975; this survey was repeated 18 months later in 1977. In the later survey the incidence of trimethoprim resistance had increased significantly, and the proportion of strains carrying R-factors conferring trimethoprim resistance had nearly doubled. The pattern ...

Identification of the type I trimethoprim-resistant dihydrofolate reductase specified by the Escherichia coli R-plasmid R483: comparison with procaryotic and eucaryotic dihydrofolate reductases.

We have isolated and determined the nucleotide sequence of a 1,626-base-pair fragment from R-plasmid R483 which encodes a trimethoprim-resistant dihydrofolate reductase. Analysis of the nucleotide sequence of this fragment revealed the presence of two open reading frames, each sufficient to encode polypeptides of approximately 17,000 daltons. Both open regions are preceded by sequences conformi...

Low trimethoprim susceptibility of anaerobic bacteria due to insensitive dihydrofolate reductases.

All the 28 Bacteroides fragilis strains investigated were susceptible to sulfamethoxazole (minimal inhibitory concentration < 16 mug/ml) and resistant to trimethoprim (TMP; minimal inhibitory concentration > 4 mug/ml). Synergism between sulfamethoxazole and TMP was present in all strains at a ratio of 1:1. The few clostridia investigated proved more resistant to both compounds. Dihydrofolate re...

Protein expression in Escherichia coli minicells containing recombinant plasmids specifying trimethoprim-resistant dihydrofolate reductases.

Deoxyribonucleic acid fragments containing the structural genes for several trimethoprim-resistant dihydrofolate reductases from naturally occurring plasmids were inserted into small cloning vehicles. The genetic expression of these hybrid plasmids was studied in purified Escherichia coli minicells. The type I dihydrofolate reductase, encoded by plasmid R483 and residing within transposon 7 (Tn...

Mechanism of R factor-mediated chloramphenicol resistance.