Occupational exposure: there for your protection.
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Biomedical subjects
Publications and source records attributed to A Paull.
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The Bactec MGIT 960 (Becton-Dickinson, UK) automated mycobacterial liquid culture system was compared with the Bactec 9000 MB (Becton-Dickinson) in order to assess ease of use, diagnostic reliability and safety features. One thousand twenty-nine clinical specimens were cultured in parallel, yielding a total of 125 (12.1%) mycobacterial isolates, including 71 Mycobacterium tuberculosis and 18 Mycobacterium avium. The Bactec MGIT 960 demonstrated a mycobacterial recovery rate and speed of detection equivalent to that of the Bactec 9000 MB for clinically important isolates. The Bactec MGIT 960 integrates smoothly into laboratory workflow, does not require needle inoculation and has a much larger capacity than the Bactec 9000 MB.
From 1987 to 1994, 16 of 162 cystic fibrosis (CF) patients attending CF clinics at three different hospitals in South Wales, U.K. were found to have respiratory secretions colonized with Burkholderia cepacia (B. cepacia). Bacteriological typing by polymerase chain reaction (PCR) ribotyping demonstrated seven strains of B. cepacia among these 16 CF patients. This typing confirmed that cross-infection was the mechanism of colonization in six of the nine patients who were colonized at the paediatric CF clinic at the University Hospital of Wales in Cardiff, and in three of the six patients who were colonized at the adult CF clinic at Llandough Hospital in Cardiff (cross-infection rate nine of 16 patients or 56%). A search was made for a nosocomial source, with screening of wards and clinics. Swabs from fomites produced four positive cultures for B. cepacia. Two isolates had the same PCR ribotype as that of the previous CF room occupant. To establish prevalence of B. cepacia among CF children living throughout Wales, respiratory secretions were cultured from 151 of 186 CF children (age < 16 years). This failed to demonstrate B. cepacia colonization other than in the CF patients already identified.
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Burkholderia cepacia is a recognised cause of respiratory failure in patients with cystic fibrosis. The value of routine use of selective enrichment broth to increase the yield of B cepacia from cystic fibrosis sputa was investigated. Two hundred sputa from 86 adult and paediatric patients were cultured onto B cepacia selective agar and also in enrichment broth. The enrichment broths were subcultured after incubation onto B cepacia selective agar. Fourteen sputa from eight patients yielded B cepacia. In all cases the isolate was recovered from the primary selective agar as well as the enrichment broth subcultures. The routine use of enrichment for cystic fibrosis sputa is of unproven benefit and increases laboratory costs.
A convenient dipstrip method (Bacteruritest; Mast Diagnostics) for bacterial quantification was evaluated with 42 endotracheal aspirates. For 31 specimens, the dipstrip method yielded counts within a 10-fold range of surface plate counts. Two specimens yielded counts by the dipstrip within a 100-fold range of plate counts. Six specimens yielded confluent growth at the greatest dilution tested by the dipstrip method, and counts > 10(10) cfu/ml in the surface plate method. Three specimens yielded no detectable growth by the dipstrip and surface plate counts < 10(2) cfu/ml. Dipstrips provide a cheap, convenient method for the routine quantification of the bacterial load in endotracheal aspirates.
Polymerase chain reaction (PCR) ribotyping detects differences in the intergenic spacer between the 16S and 23SrRNA genes. This method was applied to Burkholderia cepacia isolates from 16 Welsh cystic fibrosis (CF) patients attending three different clinics. Amplification of the intergenic spacer followed by an additional digestion step with TaqI restriction endonuclease identified seven distinct electrophoretic patterns among the patient isolates. Each of the seven patterns was distinct from that of the so called "epidemic strain" commonly isolated from patients attending clinics elsewhere in the UK. Two environmental isolates from the hospital clinics and four NCTC reference strains gave different patterns. The simplicity of the method lends itself to use in a general microbiological laboratory.
The in-vitro susceptibilities of aerobic bacteria isolated from 1804 blood and 4529 urine specimens collected at nine hospitals in the UK were examined. An agar dilution method was used to determine the MICs of each isolate to three cephalosporins, cefotaxime, cefuroxime and ceftazidime, and to two fluoroquinolones, ofloxacin and ciprofloxacin. Sensitivities were then calculated using British Society for Antimicrobial Chemotherapy recommended breakpoints. Of the cephalosporins tested cefotaxime was the most active against the Enterobacteriaceae. All the systemic staphylococcus isolates collected were sensitive to both cefotaxime and cefuroxime. As expected, ceftazidime was the only cephalosporin active against the Pseudomonas isolates. Both quinolones were highly active against the Enterobacteriaceae and Pseudomonas spp. They also demonstrated good Gram-positive activity, particularly against Staphylococcus aureus and Enterococcus spp.
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The activity of penicillin alone and combined with aminoglycoside on endocarditis strains of streptococci was examined. Good assay reproducibility was obtained by the use of logarithmic phase cultures standardised by opacity, careful inoculation of well-plates, removal of antibiotic by membrane transfer and incubating survival counts in hydrogen plus carbon dioxide. The use of 10-fold intervals for penicillin concentration simplified assay design without loss of efficiency.
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When the incubation period of primary isolation plates was extended to 48 h, mucoid strains of Pseudomonas aeruginosa were found in specimens from various infected sites in patients who did not have cystic fibrosis. The 17 mucoid isolates were characterised in terms of mucoid type, pyocin type, and their sensitivity or resistance to seven beta-lactam and two aminoglycoside antibiotics. The carbohydrate, uronic acid (alginate) and protein content of the water-soluble extracellular material of 15 strains was determined. This material was fractionated by ion-exchange chromatography, and the presence of alginate confirmed by the chemical assay of uronic acids and their quantitation by gas-liquid chromatography. Uronic acids were absent from a non-mucoid revertant of one strain. The strains produced alginate with a high content of mannuronic acid and substituted with O-acetyl groups. By proton nuclear magnetic resonance (1H-nmr) analysis the alginate from three strains was shown to lack polyguluronate blocks in its structure. These properties are also found in the alginate of mucoid P. aeruginosa strains from patients with cystic fibrosis.
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Current methods of measuring bactericidal antibiotic synergy are particularly susceptible to error because of their use of arbitrary endpoints and criteria; their results are not easily tested for statistical significance and the procedures require considerable time and effort. A single-stage method is described in which bacteria are exposed to antibiotics for a short period and then transferred twice to drug-free medium by means of a filter membrane. The results are available the next day in the form of survival counts which can be compared statistically. In an examination of 21 strains of faecal streptococcus exposed to penicillin and gentamicin the bactericidal synergy observed was smoothly variable, a finding with a bearing on the management of infections with this organism, in that the recognition of strains showing an intermediate degree of synergy is possible.
Cystic fibrosis patients with Pseudomonas aeruginosa chest infections were treated with ceftriaxone alone or ceftriaxone plus tobramycin. P. aeruginosa strains isolated before and after treatment were studied for changes in sensitivity to ceftriaxone. After therapy with either the single agent or the combination six strains from five patients were found to be resistant to ceftriaxone. No resistant strains were isolated before therapy. Resistance was mediated by excess production of Id beta-lactamase which in five of six strains was permanently derepressed. Bacterial resistance appearing during therapy reduces the value of this antibiotic in cystic fibrosis chest infections.
Fifteen patients with acute exacerbation of rheumatoid arthritis each received a 1 g bolus intravenous injection of ceftriaxone. Serum and synovial fluid was sampled at intervals between 1 h and 24 h later and assayed for ceftriaxone. Synovial fluid leucocyte counts and albumin content were measured concomitantly. Detectable levels of ceftriaxone were found in synovial fluid and serum 24 h after injection. Synovial fluid ceftriaxone concentration ranged between 66% and 100% of the concomitant serum levels. No correlation was observed between synovial fluid ceftriaxone concentration and synovial fluid leucocyte count and albumin concentration.