Biomedical subjects
B I Duerden
Publications and source records attributed to B I Duerden.
Analysis of Bacteroides species by pyrolysis mass spectrometry.
Two methods for the classification of isolates of the Bacteroides fragilis group were compared in a study of 133 clinical isolates and 10 reference strains. There was broad similarity between the pattern of clusters in pyrolysis mass spectrometry (PyMS), which reflects whole-cell composition, and that in conventional tests, which reflect nutritional interactions with the environment. A single large cluster was resolved by both approaches; this cluster comprised mainly strains identified as B. fragilis and was surrounded by a multiplicity of small clusters (42 in PyMS and 24 in conventional tests). Individual clusters corresponding to strains identified as Bacteroides thetaiotaomicron and Bacteroides vulgatus, respectively, were found by both techniques. However, for the remainder of strains, little correlation was evident between clustering in PyMS and that in conventional tests. Further comparison with data obtained by sodium dodecyl sulfate- polyacrylamide gel electrophoresis for this collection of strains showed equal levels of disagreement between classification based on whole-cell protein and each of the classifications described here. In previous studies of other genera, PyMS-based and conventional test-based classifications showed good agreement. It appears that the B. fragilis group presents intractable problems in phenotypic characterization.
Role of the reference laboratory in susceptibility testing of anaerobes and a survey of isolates referred from laboratories in England and Wales during 1993-1994.
Methods for susceptibility testing of anaerobes and their patterns of susceptibility remain debatable. The responsibilities of the Public Health Laboratory Service Anaerobe Reference Unit include identification of referred isolates; development of methods; monitoring of the occurrence of anaerobic infections; performance of taxonomic studies; maintenance of a reference collection; and monitoring of the antibiotic susceptibility of clinical isolates. Selection of antibiotics for anaerobic infections is often based upon the findings of batch tests on referred isolates in specialized centers. If the information gathered is to be a reliable guide, there should be a structured rolling survey of clinical isolates from a wide range of hospital laboratories. Strains of Bacteroides, Prevotella, Clostridium, and Propionibacterium species and peptostreptococci referred to the Anaerobe Reference Unit during 1993-1994 were tested with the Etest to determine the minimum inhibitory concentrations of metronidazole, penicillin, amoxicillin/clavulanate, cefoxitin, imipenem, erythromycin, clindamycin, and tetracycline. Metronidazole susceptibility (generally) and penicillin resistance among Bacteroides species were consistent findings, and most isolates were susceptible to imipenem, but other results varied between and within species.
Typing of 143 isolates from 10 species of Bacteroides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins.
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Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of EDTA-extracted cell-surface protein antigens is a simple and reproducible method for typing Clostridium difficile.
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Correlation of pyrolysis mass spectrometry and outer membrane protein profiles of Clostridium difficile.
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Chemoprophylaxis for skin surgery.
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Artefactual resistance to metronidazole in anaerobes of the Bacteroides fragilis group.
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Classification of oral pigmented anaerobic bacilli by pyrolysis mass spectrometry and biochemical tests.
Clinical (66) and reference (5) strains of pigmented gram-negative anaerobic bacilli, identified as Prevotella intermedia (47), Pr. melaninogenica (1), Pr. corpora (8), Porphyromonas asaccharolyticus (12), P. endodontalis (1) and P. gingivalis (2), were examined by pyrolysis mass spectrometry (PMS) and in conventional tests. Numerical classification based on conventional test reaction patterns (CTRPs) resolved five clusters, four comprising strains identified as Pr. intermedia, Pr. corpora, Pr. melaninogenica, and P. gingivalis respectively, and one comprising strains identified as P. asaccharolyticus and P. endodontalis. Numerical classification based on PMS showed a similar division, with decreasing homogeneity of chemical composition in the order Pr. intermedia, Pr. corpora, P. asaccharolyticus, which agreed with the order of homogeneity in CTRPs. PMS clusters corresponding to the genus Porphyromonas were clearly distinct from those of the genus Prevotella. PMS and CTRP classification disagreed on cluster membership for six strains. PMS identification from blind challenge sets was in agreement with conventional identification for 64 of 67 strains.
Characterisation of non-pigmented species of the genus Prevotella by polyacrylamide gel electrophoresis.
Gram-negative anaerobic bacilli previously known as the melaninogenicus-oralis group of Bacteroides have been assigned to a new genus, Prevotella. The non-pigmented members of this genus share several general characteristics and cannot be readily distinguished by routine tests. A polyacrylamide slab gel electrophoresis procedure, with visual analysis of protein patterns, was used to compare cellular protein patterns from clinical isolates with those from collection (reference) strains. Reference strains of P. oralis, P. veroralis, P. buccalis, P. oris, P. buccae, P. zoogleoformans, P. bivia, P. disiens, P. oulora, B. (P.) capillus and B. (P.) pentosaceus, and 91 non-pigmented isolates from patients with adult periodontal disease were examined by conventional biochemical tests, gas-liquid chromatography (GLC) and enzyme tests, and whole-cell protein profiles were obtained by SDS-PAGE. There was close correlation between patterns of results in biochemical and GLC tests and the SDS-PAGE profiles, and the species were readily distinguished in SDS-PAGE. The periodontal isolates were assigned to 10 groups by conventional test reaction patterns and nine groups by SDS-PAGE; the profiles of 79 isolates corresponded to those of seven species reference strains. By SDS-PAGE, clinical isolates of P. buccae (42 isolates) and P. oralis (eight isolates) showed good similarity with reference strains. However, for P. veroralis (15), P. oris (7), P. bivia (4), P. zoogleoformans (2) and P. buccalis (1), clinical isolates showed some minor variations from reference strains. Twelve isolates remained undesignated in SDS-PAGE analysis. Variant SDS-PAGE profiles divided clinical isolates of P. buccae into two subgroups and those of P. veroralis into five subgroups.
A pyrolysis mass spectrometry study of the non-pigmented Prevotella species.
Collection strains (21) and non-pigmented clinical isolates (96) provisionally identified as Prevotella spp. were classified numerically on the basis of pyrolysis mass spectrometry (PMS) data and reaction patterns in conventional tests (CTRPs) for volatile and non-volatile fatty acids, pre-formed enzymes and biochemical activity. PMS and CTRP classifications were compared with a previous classification based on visual analysis of SDS-PAGE patterns. Although the order of clusters differed, cross-tabulation of cluster membership revealed strong correlations between classifications. Cluster membership in the PMS classification correlated particularly well with SDS-PAGE results. CTRP clusters corresponded largely to the recognised species of Prevotella, but PMS and SDS-PAGE divided two species into sub-groups: two in P. buccae and five in P. veroralis. The latter subgroups could be discriminated by small but consistent differences in CTRPs. An undesignated, well differentiated cluster of strains appeared closest to the main group of P. buccae strains in PMS and CTRPs. B. (P.) capillus could not be distinguished from P. buccae; these species are regarded as synonymous. Strains of P. zoogleoformans and B. (P.) pentosaceus were well separated from other strains in PMS. A complex comprising clusters of P. disiens, P. oralis, P. veroralis, P. loescheii and a further undesignated group similar to P. melaninogenica was well differentiated from P. buccae and P. oris in PMS; clusters corresponding to P. bivia, P. corporis, P. intermedia and P. denticola formed another complex.
Virulence properties of Escherichia coli strains isolated from patients with inflammatory bowel disease.
Escherichia coli strains cultured from 74 patients with inflammatory bowel disease at different stages of disease activity (Crohn's disease (40), ulcerative colitis (34)) and 18 healthy controls were studied in relation to haemolysin and verotoxin production and enteroadherence. Disease activity was assessed by standard clinical and laboratory tests. Haemolytic E coli were isolated from 18% of patients with Crohn's disease, 24% with ulcerative colitis, and 11% of healthy controls. None of these differences was significant. No verotoxin producing strains were detected among the 216 E coli isolates examined but the extract from five strains (Crohn's (4), ulcerative colitis (1) produced a distinctive cytopathic effort on Vero cell monolayers which was later shown not to be due to verotoxin. The adhesion indices of E coli isolates cultured were: mean (SEM) 42.2 (6.4) for Crohn's disease, 43.3 (6.2) for ulcerative colitis, and 11.3 (2.0) for normal controls (p less than or equal to 0.0001). Adhesive E coli were isolated from 62% of patients with Crohn's disease and 68% with ulcerative colitis but from only 6% of normal controls (p less than or equal to 0.0002). Neither haemolysin production nor enteroadherence was dependent upon disease activity, disease location, sulphasalazine treatment, or previous intestinal resection. These results indicate that only enteroadherent E coli were frequently associated with inflammatory bowel disease; their relation to the pathogenesis of these conditions, however, remains uncertain.
Prophylactic antibiotics for skin surgery?
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The assessment of faecal flora in patients with inflammatory bowel disease by a simplified bacteriological technique.
A semi-quantitative bacteriological method was used to study faecal flora in 42 patients with Crohn's disease, 37 with ulcerative colitis and 21 healthy controls. Faecal homogenates were plated on primary isolation plates by a technique that allowed the growth of various microbial isolates to be assessed on a visual 1(+)-5+ score. This method was first calibrated against a standard quantitative bacteriological technique, which confirmed the reliability and reproducibility of the results obtained by the simpler method. Patients with clinically active Crohn's disease (22) had significantly higher total aerobe scores than patients with quiescent disease (20) (p less than or equal to 0.006) or ulcerative colitis (p less than or equal to 0.04) or normal controls (p less than or equal to 0.02). The scores of Escherichia coli were parallel to those of total aerobes. Lactobacillus and bifidobacteria scores were significantly reduced in patients with Crohn's disease compared to those with ulcerative colitis and controls. The anaerobic flora in both Crohn's disease and ulcerative colitis was indistinguishable from that of controls. Bacteroides vulgatus and B. fragilis were the predominant bacteroides in all groups. Patients with ulcerative colitis, regardless of disease activity, harboured faecal flora that did not differ from that of normal controls. The abnormal faecal flora in Crohn's disease did not correlate with established clinical and laboratory indicators of disease activity.
Susceptibility of Haemophilus ducreyi to spermicidal compounds, in vitro.
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Isolation of Bacteroides ureolyticus from the genital tract of men with and without non-gonococcal urethritis.
Urethral specimens from 247 heterosexual men--118 patients with non-gonococcal urethritis and 129 controls with no evidence of urethritis--were examined for the presence of Bacteroides ureolyticus. Bacteroides ureolyticus was isolated from 45 (34.9%) of the controls and from 31 (26.3%) of the urethritis patients; there was no significant difference between these rates (p = 0.1). There was no association between the density of Bacteroides ureolyticus on primary isolation plates in either group.
A pyrolysis-mass spectrometry study of Corynebacterium spp.
Clinical (66) and collection (38) strains of Corynebacterium spp., including C. jeikeium and CDC group D2, and of Listeria monocytogenes were examined. Conventional characters used in species identification were assessed by a microbiochemical method, and pyrolysis-mass spectrometry (Py-MS) was performed with a Horizon Instruments PYMS 200X. Classification based on Py-MS data yielded clusters that corresponded with species identification and classification groups from conventional data. One small group of clinical strains, homogeneous in conventional tests and Py-MS, comprised isolates from sputum samples from patients undergoing ventilation; they were similar to collection strains of C. renale and C. striatum; the latter species has been implicated in chest infection. Another group, similar to C. minutissimum in both systems, comprised clinical strains isolated from urogenital specimens. L. monocytogenes strains were clearly distinct from Corynebacterium spp. Groups comprising CDC D2 strains and C. jeikeium were resolved, and were similar to other Corynebacterium spp. Two collection strains of C. xerosis were distinct in conventional tests and Py-MS.
Bacterial reservoirs in cystic fibrosis.
To establish whether colonisation of the upper respiratory tract or bacterial contamination of inhaler devices or solutions predisposes to colonisation of the lower respiratory tract in patients with cystic fibrosis, bacterial isolates from groups of children who were positive (n = 13) or negative (n = 18) for Pseudomonas aeruginosa were studied. Cultures of swabs from inhaler devices, toothbrushes, and upper airways were compared with cough swabs or sputum cultures. No pathogens were obtained from inhaler equipment administering unit dose medications. Upper airway carriage of Staphylococcus aureus and Haemophilus influenzae was identified in both groups but correlated poorly with sputum isolates. P. aeruginosa was found only in the upper respiratory tract of children with established colonisation of the lower airways. No P aeruginosa isolates were obtained from the upper airways of the group with negative sputum, including one patient who became colonised by P aeruginosa during the study. Our results did not support the suggestion that colonisation of the upper respiratory tract by P aeruginosa predisposes to colonisation of the lower airways. Failure to isolate pathogenic organisms consistently from the upper airways in patients with positive sputum argues against a local epithelial factor predisposing to bacterial colonisation.