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D J Platt

Publications and source records attributed to D J Platt.

52 records · Page 3Linked to original sources
PubMed1984

Antimicrobial resistance and the ecology of Escherichia coli plasmids.

Four hundred and seven clinical isolates of Escherichia coli were examined for the presence of plasmids. These isolates comprised 189 which were collected irrespective of antimicrobial resistance (VP) and 218 which were collected on the basis of high-level trimethoprim resistance (TPR). The VP isolates were divided into drug sensitive (VPS) and drug-resistant (VPR) subpopulations. Plasmids were detected in 88% of VP isolates (81% of VPS and 94% of VPR) and 98% of TPR isolates. The distribution of plasmids in both groups and subpopulations was very similar. However, there were small but statistically significant differences between the plasmid distributions. These showed that more isolates in the resistant groups harboured plasmids than in the sensitive subpopulation (VPS) and that the number of plasmids carried by resistant isolates was greater. Multiple drug resistance was significantly more common among TPR isolates than the VPR subpopulation and this was paralleled by increased numbers of plasmids. Fifty-eight per cent of VPR and 57% of TPR isolates transferred antimicrobial resistance and plasmids to E. coli K12. Of the R+ isolates, 60% carried small plasmids (MW less than 20Md) and 52% of these co-transferred with R-plasmids. These results are discussed.

Ampicillin↗
PubMed1984

Sequential acquisition of R-plasmids in vivo by Salmonella typhimurium.

Salmonella typhimurium, resistant only to trimethoprim and sulphamethoxazole, was isolated from the faeces and blood of a chronic alcoholic patient in acute renal failure. The isolates harboured an 18 Md non-conjugative plasmid. He was dialysed peritoneally and treated with ampicillin; four days later there was no clinical improvement and his peritoneal dialysis fluid (PDF) had become infected. Salm. typhimurium was isolated from faeces and PDF. Both isolates were additionally resistant to ampicillin and contained two plasmids (55 Md and 18 Md). Therapy was changed to chloramphenicol and gentamicin was added to the PDF. Two weeks later Salm. typhimurium was again isolated from PDF and faeces. The PDF isolate was unchanged but 4% of the colonies isolated from this faecal specimen were resistant to chloramphenicol and had acquired an additional 62 Md plasmid. From all PDF and faecal specimens two different strains of Escherichia coli and one strain of Klebsiella pneumoniae were isolated which contained plasmids indistinguishable, on the basis of molecular weight and transferable resistance markers, from those acquired by Salm. typhimurium. The transferability of these plasmids in vitro to E. coli K12 and to the patient's initial Salm. typhimurium was studied and the results discussed.

Anti-Bacterial Agents↗
PubMed1984

Distribution and transferability of plasmids in trimethoprim-resistant urinary strains of Escherichia coli: a comparative study of hospital isolates.

Trimethoprim-resistant urinary isolates of Escherichia coli, collected in 1982, were studied and the results compared with those obtained for isolates collected during the period 1979-1980. Ninety-eight (81%; a 10% increase) were resistant to trimethoprim 1024 micrograms/ml and 93 (95%) were also resistant to sulphamethoxazole 1024 micrograms/ml. The frequency distributions of plasmids were similar in both collections although there was a significant increase in the number of small plasmids (mol. wt less than or equal to 20 X 10(6] in the 1982 collection. Transfer of resistance was associated with isolates that carried larger numbers of plasmids. A significantly smaller proportion of isolates in this, than in the earlier series, transferred trimethoprim resistance to E. coli K12 suggesting continued transposition of trimethoprim resistance on to the bacterial chromosome. Fifteen different trimethoprim resistance plasmids were identified, of which five, including that found most frequently, were common to both collections. Plasmids which transferred trimethoprim resistance without sulphonamide resistance were more common in the 1982 series. Plasmids which transferred linked trimethoprim and streptomycin resistances, in particular those not carrying other resistance markers, were less common in the 1982 series of isolates. Although the majority of E. coli isolates highly resistant to trimethoprim remained resistant to sulphonamide, our results suggested changes in the genetic location and linkage of the resistance markers.

Anti-Bacterial Agents↗
PubMed1983

The isolation of thymidine-requiring Haemophilus influenzae from the sputum of chronic bronchitic patients receiving trimethoprim.

Two different strains of thymidine-requiring Haemophilus influenzae (thy-) were isolated from the sputum of two patients with chronic obstructive airways disease, during therapy with oral trimethoprim for the treatment of an acute exacerbation of chronic bronchitis. Both patients responded clinically. Since trimethoprim levels in sputum and serum were very low the patients were probably non-compliant. Isolates of H. influenzae prototrophic for thymidine (thy+) were isolated from both patients in remission before, at the onset of exacerbation and also within two weeks of stopping therapy. Thy- and thy+ isolates from the same patient were of identical biotype but isolates from the two patients were of different biotypes. The minimum inhibitory concentration (MIC) of trimethoprim for the thy+ isolates obtained after therapy was significantly higher than the MIC for the isolates obtained at the onset of exacerbation. Thy- isolates were further investigated and a novel mechanism of low-level trimethoprim resistance is proposed.

Ampicillin↗
PubMed1983

Characterization of spontaneous resistant variants of Serratia marcescens selected in the presence of carbenicillin.

Spontaneous carbenicillin-resistant variants were isolated from pigmented Serratia marcescens GRI 2677 with frequencies as high as 1 in 7.4 x 10(4). One-hundred and thirteen such variants were characterized with respect to pigmentation, antimicrobial susceptibility and beta-lactamase production. Sixty-eight were less pigmented than the parent culture, 84 showed low level resistance to five aminoglycosides and 17 showed increased beta-lactamase activity. Thirty-three variants were unstable and reverted to the parental phenotype at high frequency. One designated GRI 2677-8, was additionally auxotrophic and was further characterized. On the basis of these criteria the variants were assigned to one of 21 sub-groups. These results are discussed in relation to resistant clinical isolates and a possible mechanism that explains the diversity of variants.

Aminoglycosides↗
PubMed1983

Distribution and transferability of plasmids in trimethoprim resistant urinary Escherichia coli.

Urinary isolates of Escherichia coli that were resistant to trimethoprim were collected in Glasgow Royal Infirmary during 1979 and 1980. Eighty-eight were resistant to trimethoprim 1024 micrograms/ml and 80 (92%) were also resistant to sulphamethoxazole 1024 micrograms/ml; 73% were multiresistant. Plasmids were detected in 98% of strains and 60% carried two or more. Half of the isolates transferred trimethoprim resistance to E. coli K12 and 70% of these cotransferred resistance to sulphonamide although these markers were often not linked. Trimethoprim resistance was carried on 12 different plasmids, four of which also conferred sulphonamide resistance. All except two carried streptomycin resistance which suggests that Tn7 was probably present. The results are discussed in relation to current prescribing policy.

Anti-Bacterial Agents↗
PubMed1982

A study of difficult respiratory infections in general practice.

Augmentin was used to treat 40 patients in general practice with exacerbations of bronchiectasis or chronic obstructive airways disease who had not responded clinically to treatment with antimicrobial agents. After ten days treatment 15 patients (38%) were clinically free from infection, 21 (52%) had improved but their sputum still contained pus. Four patients (10%) did not respond to treatment. Pathogens were isolated from 63 per cent of the patients; Haemophilus influenzae was the most common. The clinical response was significantly better in patients from whom recognised pathogens were not isolated.

Adult↗
PubMed1980

Rectal gonorrhoea in male homosexuals. Presentation and therapy.

In a review of rectal gonorrhoea 73 episodes were studied in 65 homosexual men. The presenting signs and symptoms were carefully noted. Treatment with a single injection of spectinomycin hydrochloride 2 g resulted in a cure rate of 94.5%. The relatively high treatment failure rate associated with rectal gonorrhoea may possibly be due to microbial mechanisms.

Adolescent↗
PubMed1976

Carbon dioxide requirement of Neisseria gonorrhoeae growing on a solid medium.

A survey of 120 isolations of Neisseria gonorrhoeae from male patients showed that 47 (39%) isolates were unable to produce visible colonies without a supply of exogenous carbon dioxide. Of 63 strains, 25 strains required CO2 for isolation but none exhibited a CO2 requirement beyond subculture 4. CO2-requiring strains deprived of CO2 appeared to lose their colony-forming ability exponentially in an environment otherwise conductive to growth. The CO2 requirement was found to be linked to the initiation of growth. An agar-to-agar replica-plating device was used to study the early stages of colonial growth. The CO2 requirement was also found to correlate with the various phases of the colony growth cycle, such that it was required during lag phase, not required during the phase of rapid growth, and returned as colonies aged. These results are discussed.

Agar↗
PubMed1976

Isolation of oxidase-positive Gram-negative cocci not belonging to the genus Neisseria from the urogenital tract.

In a 12-month period, oxidase-positive, Gram-negative cocci showing similar characteristics in biochemical tests have been isolated from the urogenital tract of 39 male and female patients. Although these organisms superficially resemble Neisseria gonorrhoeae, biochemical characterization and the results of DNA base composition analysis indicate that they do not belong to the genus Neisseria. The relationship of these organisms to the genera Neisseria, Achromobacter, and Pseudomonas is discussed.

Alcaligenes↗
PubMed1976

Prevalence of multiple antibiotic resistance in Neisseria gonorrhoeae.

The susceptibility of 100 strains of Neisseria gonorrhoeae to five antimicrobial agents (penicillin, streptomycin, oxytetracycline, sulphamethoxazole, and gentamicin) was examined. Three strains were resistant to each antimicrobial, fourteen exhibited resistance to three or four of the five compounds tested, and 49 were resistant to a single agent, or to pairs of the selected agents. 34 strains were found to be fully sensitive to all of the compounds tested. It is suggested that resistance to gentamicin and sulphamethoxazole may be determined by a multiple resistance gene. The overall frequency of penicillin resistance was found to be 26-5 per cent (MIC greater than 0-06 mug/ml.), suggesting a significant decrease in resistance since 1968.

Anti-Bacterial Agents↗