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Biomedical subjects

S G Amyes

Publications and source records attributed to S G Amyes.

At least 145 records · Page 8Linked to original sources
PubMed1985

The effect of a range of antimicrobial drugs on the haemagglutination of two clinical isolates from urinary tract infections.

A range of nine common antimicrobial drugs were tested for their effect on adhesion of the mannose-resistant haemagglutination-positive Proteus vulgaris strain BH77 and Escherichia coli strain BH121, isolated from patients with urinary tract infections. Minimum inhibitory concentrations of the antimicrobials for these strains were determined in Mueller-Hinton broth and the effect of each antimicrobial, at the quarter MIC values, on the haemagglutination of the strains was then determined. Haemagglutination could only be prevented by inhibitors of protein synthesis. After the introduction of an R-plasmid into strain BH121 this effect was annihilated. When the new MICs were determined, the inhibition was still observed at the new quarter MIC values.

Anti-Infective Agents, Urinary↗
PubMed1982

Bactericidal activity of trimethoprim alone and in combination with sulfamethoxazole on susceptible and resistant Escherichia coli K-12.

The combined effects of trimethoprim and sulfamethoxazole on the viability of Escherichia coli K-12 and resistant strains possessing resistance plasmids were examined in minimal medium. When methionine, glycine, and adenine were present, sulfamethoxazole could enhance trimethoprim activity against E. coli K-12 so that the combination was bactericidal. However, this enhancement occurred over a narrow range of trimethoprim concentrations (0.04 to 0.2 mg liter-1) and only when the sulfamethoxazole concentration was more than 10 times that of trimethoprim. Under certain conditions, sulfamethoxazole enhanced trimethoprim bactericidal activity against E. coli K-12 carrying plasmid R1 at concentrations of sulfamethoxazole far below those required to inhibit the organism, but there was no such enhancement with the same host containing the SSu plasmid. Similar differences were found with strains possessing trimethoprim resistance plasmids R483 and R751. Sulfamethoxazole can promote a bactericidal response with trimethoprim in E. coli K-12 and some of its resistant derivatives, but only under a narrow range of concentrations.

Culture Media↗
PubMed1981

Co-trimoxazole susceptibility tests improved with separate trimethoprim and sulfamethoxazole disks.

It is impossible to test accurately bacterial susceptibility to the trimethoprim-sulfamethoxazole combination co-trimoxazole with a single combined susceptibility disk. However, a variety of factors still affect the result even when separate trimethoprim and sulfamethoxazole disks are used. Experiments with separate disks showed that the optimum conditions for testing the susceptibilities of enterobacteria to these drugs were to flood-seed an agar plate with an inoculum of 10(4) to 10(5) organisms per ml, take off the excess liquid, and place a disk of 1 microgram of trimethoprim and another of 50 micrograms of sulfamethoxazole on the surface of the agar with their centers exactly 25 mm apart. This method not only allowed the determination of resistance but also distinguished synergy.

Drug Combinations↗
PubMed1981

Co-trimoxazole sensitivity testing: comparison of separate and combined disk agar diffusion techniques.

Five hundred and seven strains of bacteria isolated from the urine of patients with significant bacteriuria (more than 10(8) colony-forming units per litre) were tested for sensitivity to co-trimoxazole by the agar diffusion technique. Each organism was tested with a combined disk containing trimethoprim and sulphamethoxazole in a primary sensitivity test and, at a standardised inoculum, with both a combined disk and separate disks of trimethoprim and sulphamethoxazole. The results show that combined disk testing does not always indicate the sensitivity patterns of the organisms being tested.

Agar↗
PubMed1978

R-factor mediated dihydrofolate reductases which confer trimethoprim resistance.

Six different R-factors conferring trimethoprim resistance had been isolated from a variety of sources. The trimethoprim-resistant dihydrofolate reductases (EC 1.5.1.3) from strains containing these R-factors were purified by ammonium sulphate precipitation and DEAE-cellulose ion-exchange chromatography. The enzymes showed no significant differences in molecular weight, pH profile, substrate profile, heat sensitivity, inhibition profile and Michaelis-Menten kinetics. There was, however, considerable variation in the specific activity of these enzymes in the same bacterial host. When two Escherichia coli trimethoprimsensitive dihydrofolate reductases were examined as controls, considerable differences between their properties and those of the enzymes mediated by R-factors were detected. The data suggest that one trimethoprim resistance gene could be spreading through the bacterial population, possibly situated on a transposon.

Escherichia coli↗
PubMed1978

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 of resistances associated with R-factor trimethoprim resistance also changed betweeen these two surveys.

Bacteria↗
PubMed1976

The purification and properties of the trimethoprim-resistant dihydrofolate reductase mediated by the R-factor, R388.

The R-factor R388 mediates the production of a trimethoprim-resistant dihydrofolate reductase. This enzyme has a different molecular weight and pH profile to the trimethoprim-sensitive enzyme of the Escherichia coli host. The R-factor mediated enzyme was separated completely from the host E. coli enzyme by DEAE-cellulose ion-exchange chromatography. The purified R-factor enzyme was about 20 000 times less susceptible to trimethoprim than the E. coli enzyme and although it was inhibited competitively by trimethoprim, its inhibitor constant (Ki) was 20 000 times greater than that of the host enzyme. The R388 and E. coli enzymes also differed in their substrate specificity requirements. In addition, the R388 enzyme suprisingly conferred high level resistance to the broad spectrum dihydrofolate reductase inhibitor, amethopterin. The possible origins of the R388 enzyme are discussed.

Drug Resistance, Microbial↗