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Biomedical subjects

S G Amyes

Publications and source records attributed to S G Amyes.

At least 73 records · Page 4Linked to original sources
PubMed1993

The role of thymine starvation in the expression of type IV plasmid-encoded trimethoprim-resistant dihydrofolate reductase.

Hyperproduction of the type IV plasmid-encoded dihydrofolate reductase was studied in Escherichia coli J62-2 (pUK1123). Hyperproduction of the enzyme was shown to occur not simply as a response to a given concentration of trimethoprim but also to the presence of thymidine in the medium. Before hyperproduction occurred the bacteria began to elongate and die, thus showing the symptoms of thymine starvation. Hyperproduction also required the presence of L-methionine, adenine and glycine, suggesting that the elevated production of the enzyme was a response to the ability of trimethoprim to starve the cell of thymine metabolites.

Adenine↗
PubMed1993

The induction of trimethoprim resistance encoded by the type IV dihydrofolate reductase gene.

The effect of plasmid pUK1123, which confers low level resistance to trimethoprim when tested on solid minimal medium, but also no resistance when tested on IsoSensitest agar, was investigated in liquid media. The growth of Escherichia coli J62-2, harbouring pUK1123, was unaffected in liquid minimal medium containing trimethoprim 10 mg/L. However, in IsoSensitest broth, exposure to this drug concentration resulted in bacteriostasis. After an initial delay, resistance to trimethoprim was induced in IsoSensitest broth containing trimethoprim 10 mg/L, by the imposition of thymine starvation. This response was immediately reversible when trimethoprim was removed, confirming that resistance resulted from induction rather than selection of resistant mutants.

Culture Media↗
PubMed1993

Effect of sub-inhibitory concentrations of antibiotics on the virulence of Staphylococcus aureus.

The production of virulence factors by various bacteria can be influenced by sub-inhibitory concentrations of antibiotics. The effect of six antibiotics on the production of representative extracellular enzymes and toxins produced by Staphylococcus aureus was investigated. The production of the virulence determinants coagulase, protein A, alpha and delta haemolysin was monitored in the presence of ciprofloxacin, enoxacin, chloramphenicol, gentamicin, tetracycline and methicillin. The protein synthesis inhibitors reduced the production of coagulase and protein A, and almost completely inhibited the production of the haemolysins. Haemolysin production was also reduced by ciprofloxacin and enoxacin, but these antibiotics had little effect on the production of coagulase and protein A. Methicillin stimulated the production of alpha and delta haemolysins but had no effect on the production of coagulase and protein A.

Anti-Bacterial Agents↗
PubMed1993

Comparative antibacterial spectrum of trimethoprim and brodimoprim.

Brodimoprim is a new 2,4-diaminobenzylpyrimidine that selectively inhibits bacterial and resistance plasmid dihydrofolate reductases to a similar or greater extent than trimethoprim. Brodimoprim reaches equivalent levels in the serum as trimethoprim for the same dosage regimens but, unlike trimethoprim, brodimoprim has a long half-life. Brodimoprim has a similar antibacterial spectrum to trimethoprim against bacterial species normally sensitive to this class of drugs although it is not active against aerobic bacteria that are normally inherently trimethoprim-resistant, such as Pseudomonas spp. Against a range of strains of the Enterobacteriaceae trimethoprim was slightly more active, although in an in vivo murine model brodimoprim had a significantly better cure rate. Brodimoprim was 2-4-fold more active against several strains of Neisseria, Nocardia, Vibrio cholerae, Bacteroides and other anaerobes. In particular the MIC90 values of brodimoprim for Clostridium and Fusobacterium spp were lower than those of trimethoprim.

Animals↗
PubMed1992

TRC-1: emergence of a clavulanic acid-resistant TEM beta-lactamase in a clinical strain.

A novel TEM-derived plasmid-encoded beta-lactamase, resistant to inhibition by clavulanic acid, has been identified in a clinical strain of Escherichia coli found in Scotland. The beta-lactamase gene was carried on an 81-kb plasmid that conferred no other resistances. The novel enzyme conferred resistance to the amoxycillin/clavulanic acid combination on the host bacterium. The beta-lactamase has a pI of 5.25 and lies between the PSE-4 and SAR-1 beta-lactamases on an isoelectric focusing gel. This beta-lactamase has a Mr value of 25,000, similar to the TEM-1 enzyme and a comparable substrate profile. Its most significant difference is that it is inhibited by clavulanic acid 100-fold less efficiently than the TEM-1 enzyme. The enzyme was confirmed to be derived from the TEM enzymes by probing the plasmid DNA with an intragenic gene probe for TEM-1. This is the first report of a clinical bacterium carrying a TEM-enzyme that confers resistance to clavulanic acid combinations and we have designated the beta-lactamase as TRC-1.

Clavulanic Acid↗
PubMed1992

Outbreak of infection in two UK hospitals caused by a strain of Klebsiella pneumoniae resistant to cefotaxime and ceftazidime.

During an 8-month period, Klebsiella pneumoniae resistant to cefotaxime and ceftazidime were isolated from 18 elderly patients in two closely-situated UK hospitals. Amongst these 18 patients, the organisms were isolated from urine samples of 17, from blood cultures of two and from a wound swab of one. The infected patients were located in nine different wards and several of the patients had been transferred between wards, within and between the two hospitals. All the bacterial isolates belonged to serotype K62, were non-typable or reacted only weakly with bacteriophage, showed similar plasmid profiles and were resistant to tetracycline and trimethoprim, thus indicating they were the same strain. Resistance to cefotaxime and ceftazidime was inhibited by clavulanic acid suggesting the involvement of extended-spectrum beta-lactamase (ESBL) enzyme activity. This was confirmed by analytical isoelectric focusing, which showed that isolates each produced two beta-lactamases with isoelectric points of 7.0(SHV-3) and 7.6 (SHV-1/2) respectively.

Cefotaxime↗
PubMed1992

The incidence of antibiotic resistance in aerobic faecal flora in south India.

During a field study in South India in 1989, faecal specimens were collected from residents in villages and the town of Vellore in South India. Examination of the faecal specimens revealed that virtually the whole population carried commensal bacteria resistant to trimethoprim, ampicillin and chloramphenicol. Most specimens contained more than one type of bacterium resistant to each antibiotic. There was less resistance to nalidixic acid, with a higher proportion in the town (33%) than in the villages (13%). Although there was little cross-resistance of the ampicillin-resistant strains to later generation cephalosporins, 50% were resistant to the combination of amoxycillin and clavulanic acid. There was no significant cross-resistance of the nalidixic acid-resistant strains to fluorinated 4-quinolones, despite the free availability of ciprofloxacin and norfloxacin in the area. The probable reason for the high incidence of resistance to first generation antimicrobials is the extensive use of these agents, coupled with continuous exposure to large numbers of faecal micro-organisms.

Bacteria, Aerobic↗
PubMed1992

Characterization of the plasmid mediated beta-lactamase BIL-1.

A multi-resistant strain of Escherichia coli isolated from a patient from Pakistan was shown to possess a new plasmid-mediated beta-lactamase. This enzyme, designated BIL-1, conferred resistance to extended-spectrum cephalosporins such as cefotaxime and ceftazidime. However, unlike other plasmid-mediated beta-lactamases capable of conferring resistance to these drugs, the BIL-1 was not a member of the TEM or SHV group of plasmid-mediated beta-lactamases and it also conferred resistance to beta-lactam drugs in combination with beta-lactamase inhibitors (i.e. clavulanic acid). The biochemical properties of the enzyme suggest that BIL-1 is related to the Richmond & Sykes Class I chromosomal beta-lactamases. Its inhibition properties by various beta-lactam drugs are similar to the inhibition properties of the chromosomally-encoded P99 enzyme of Enterobacter cloacae.

Anti-Bacterial Agents↗
PubMed1992

The sensitivity of clinical bacteria isolated in Scotland to the oral cephalosporin, cefdinir.

The minimum inhibitory concentration (MIC) of cefdinir (CI-983, FK-482), cephalexin cefuroxime, cefixime and ceftazidime were determined against clinical isolates. Cefdinir was as effective as cefixime against Haemophilus and Moraxella (Branhamella) strains and both were more effective than cefuroxime. Against streptococci, cefdinir was much more effective than cefixime and had similar efficacy to cefuroxime. Against staphylococci, cefdinir had the lowest MIC50 of all of the drugs tested. The efficacy of these antibiotics was tested against Escherichia coli K12 strains harbouring 16 of the new extended-spectrum plasmid-mediated beta-lactamases, and cefdinir was more effective than ampicillin, cephalexin, cefuroxime, ceftazidime and aztreonam.

Administration, Oral↗
PubMed1991

Detection of novel trimethoprim resistance determinants in the United Kingdom using biotin-labelled DNA probes.

Two collections of trimethoprim R plasmids, isolated from strains of Escherichia coli during 1978-83 and 1987-8 respectively, were retrospectively screened with specific biotinylated DNA probes for the presence of genes encoding particular DHFR enzymes. The results confirmed that the type I DHFR gene was the predominant plasmid-encoded gene conferring trimethoprim resistance in strains of E. coli from the Nottingham area of the UK, but indicated that genes encoding the more recently recognized types of DHFR enzymes had appeared in the bacterial gene pool and could be recognized with increased frequency in the latter plasmid collection. This was particularly true of the type IIIa and type VII enzymes which together accounted for 27% of the trimethoprim R plasmids examined in 1987-8.

Animals↗