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D M MacLaren

Publications and source records attributed to D M MacLaren.

At least 19 recordsLinked to original sources
PubMed2000

Role of bacterial virulence factors and host factors in the outcome of Escherichia coli bacteraemia.

In a study of the role of virulence factors in the outcome of Escherichia coli bacteraemia, blood isolates from 30 hospitalised patients were characterised with regard to O and K antigens, P and type 1 fimbriae, haemolysin production, cytonecrotising factor 1 production, serum resistance, ability to activate neutrophils and resistance to killing. Patients were analysed to identify host factors contributing to morbidity and mortality. In univariate analyses the presence of a K antigen, type 1 fimbriae, absence of haemolysin production, serum resistance and resistance to killing were associated with morbidity and mortality. In multivariate analyses only the absence of haemolysin production was associated with morbidity and mortality, after taking host factors into account. These preliminary findings suggest that host factors override bacterial virulence factors in determining the course of Escherichia coli bacteraemia. The negative association between haemolysin production and clinical deterioration during Escherichia coli bacteraemia might indicate predominance of less virulent strains in patients with other risk factors for morbidity and mortality or inactivation of neutrophil products needed for host defence.

Aged↗
PubMed1998

Serotyping and genotyping of genital Chlamydia trachomatis isolates reveal variants of serovars Ba, G, and J as confirmed by omp1 nucleotide sequence analysis.

Urogenital isolates (n = 93) of Chlamydia trachomatis were differentiated into serovars and variants by serotyping with monoclonal antibodies and genotyping by restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified omp1 gene, respectively. The types of 87 of the 93 isolates (94%) were identical, as determined by both methods. Among these 87 isolates, 3 isolates were identified as the recently described new serovariant Ga/IOL-238 by omp1 nucleotide sequence analysis of the variable domains. Of the remaining six isolates, three isolates serotyped as both L2 and Ba but were identified as Ba/A-7 by genotyping by RFLP analysis of omp1. The omp1 nucleotide sequences of variable domains VD1, VD2, and VD4 of these urogenital Ba strains were identical to the sequences of the variable domains of Ba/J160, an ocular Ba type. The three remaining isolates were serotyped as J, but the patterns obtained by RFLP analysis of omp1, which were identical for the three isolates, differed from that of prototype serovar J/UW36. omp1 nucleotide sequence analysis revealed that these strains are genovariants of serovar J/UW36. Nucleotide sequence differences between serovar J/UW36 and this J genovariant, designated Jv, were found in both variable and constant domains. In conclusion, this study shows that the PCR-based genotyping of clinical C. trachomatis isolates by RFLP analysis of omp1 has a higher discriminatory power and is more convenient than serotyping. Variants of C. trachomatis serovars Ba, G, and J were identified and characterized.

Antibodies, Bacterial↗
PubMed1997

Improvement of growth of Chlamydia pneumoniae on HEp-2 cells by pretreatment with polyethylene glycol in combination with additional centrifugation and extension of culture time.

The following adaptations led to improved growth of Chlamydia pneumoniae on HEp-2 cells compared to that by the standard method: monolayer preincubation with 7% polyethylene glycol (PEG), extension of incubation time to 7 days, and extension of incubation to 7 days in combination with centrifugation on days 3, 4, and 5. These adaptations resulted in approximate increases in numbers of inclusion-forming units (IFU) of 2-, 5-, and 69-fold, respectively. A combination of preincubation with PEG, prolonged incubation, and centrifugation on days 3, 4, and 5 increased the numbers of IFU >300-fold. This is therefore recommended as the optimal method for culturing C. pneumoniae.

Bacteriological Techniques↗
PubMed1995

Effect of an acidic environment on the susceptibility of Helicobacter pylori to trospectomycin and other antimicrobial agents.

The susceptibility of 30 clinical isolates of Helicobacter pylori to trospectomycin, ampicillin, metronidazole, clarithromycin, azithromycin and clindamycin under varying pH conditions was evaluated. An acidic environment was shown to affect unfavourably the activity of all the antimicrobial agents tested. This pH effect was most marked for the two macrolides and for clindamycin.

Ampicillin↗
PubMed1995

Diversity in lipid A binding ligands: comparison of lipid A monoclonal antibodies with rBPI23.

1. Mabs with a high affinity for free lipid A do not bind when it is covalently linked, i.e. in the form of LPS. 2. Lipid A-binding Mabs may be divided into three categories: I. Monoreactive Mabs that bind to the hydrophillic backbone of lipid A II. Polyreactive Kdo Mabs III. Polyreactive Mabs that bind by hydrophobic interactions 3. rBPI23 binds either free or covalently linked lipid A.

Animals↗
PubMed1994

[Successful culture of Chlamydia pneumoniae in 2 asymptomatic patients].

In two women, partners of 41 and 36 years old, positive cultures of Chlamydia pneumoniae were repeatedly obtained from the throat. Both individuals were asymptomatic during the period described. Eradication was not achieved despite treatment with doxycycline. C. pneumoniae on the basis of serological data is considered a common cause of respiratory tract infections. However, this micro-organism has only been isolated in the Netherlands once. Carrier status has been described in the literature, although its frequency is unknown.

Adult↗
PubMed1994

Utilization of haem from the haptoglobin-haemoglobin complex by Bacteroides fragilis.

Possession of specialized iron acquisition systems is a prerequisite for the survival of pathogenic bacteria in their host. The purpose of this study was to determine whether Bacteroides fragilis, a clinically important Gram-negative anaerobic bacterium, possesses a specific haem-uptake system. Growth studies indicated that this microorganism can utilize haem from either haemoglobin or haptoglobin-haemoglobin as its sole source of iron. Iron-repressible haem-binding protein complexes (HBP complexes), involved in the uptake of haem from haptoglobin-haemoglobin were detected by means of lithium dodecyl sulfate polyacrylamide gel electrophoresis (LDS-PAGE). Four polypeptides of approximately 60, 58, 49 and 35 kDa, which are part of these HBP complexes, were identified as haem-binding proteins. A 44 kDa iron-repressible outer-membrane protein is needed for a functional HBP complex, but the exact role of this protein in the uptake of haem is still unknown.

Bacteroides fragilis↗
PubMed1994

A multicenter survey of resistance in The Netherlands using the Etest.

To obtain data about the prevalence of resistance in bacterial isolates causing serious infections in the Netherlands, a multicenter survey was carried out using the Etest for quantitative susceptibility testing. More than 6000 isolates belonging to ten species were tested against eight antibiotics. Moreover, the Etest was validated against the agar dilution method and the reproducibility of the Etest was studied. In spite of pH differences between the agar plates used for Etesting and agar dilution testing, a good correlation (that is 86%-97% within log2 dilution steps) was found between both methods. Comparison of Etest values of the participating laboratories and the reference laboratory showed > 80% conformity within 1 log2 dilution step and 90% within 2 log2 dilution steps, indicating a sufficient reproducibility of the Etest. Resistance percentages were low for most species and antibiotics, relatively high percentages (10%-20%) indicating natural insusceptibility rather than development or increase of resistance.

Anti-Bacterial Agents↗
PubMed1994

The role of neuraminidase in haemagglutination and adherence to colon WiDr cells by Bacteroides fragilis.

The role of neuraminidase in haemagglutination and adherence to colon WiDr cells by eight strains of Bacteroides fragilis and four strains of oral black-pigmented gram-negative anaerobes was studied. Neuraminidase treatment resulted in a very small increase of haemagglutination by some of the strains but had no effect on adherence to WiDr cells by all bacterial strains tested except one strain of Prevotella intermedia (HG 110). Inhibition of neuraminidase had no effect on haemagglutination or adherence, nor was any correlation found between haemagglutinating ability and neuraminidase activity in the B. fragilis strain. The results indicated that haemagglutination and adherence of B. fragilis to WiDr cells were not mediated by neuraminidase.

Bacterial Adhesion↗
PubMed1994

Frequencies of lipopolysaccharide core types in Escherichia coli strains from bacteraemic patients.

We have investigated the distribution of the various core types (R1, R2, R3, R4 and K-12) in 138 Escherichia coli isolates obtained from positive blood cultures. Rabbit antisera, raised against five rough strains expressing the respective core types, were made monospecific by extensive absorption. The reactivity of the antisera was tested in ELISA with bacterial cells that had been autoclaved for full exposure of core epitopes. One hundred and thirty strains could be typed directly, while eight strains required prior digestion with proteinase K for removal of cross-reactions. Ninety-four of the strains (68%) expressed the R1 type, and 9 (6.5%), 12 (8.7%), 7 (5.1%) and 3 (2.2%) strains expressed the R2, R3, R4 and K-12 core types, respectively. An R1R4 mixed core type, hitherto not yet described, was found in 13 (9.4%) strains. Results obtained with polyclonal antisera were in agreement with those obtained with monoclonal antibodies to the R1, R2 and R3 core types. Core typing may serve as an additional serological marker next to conventional typing of O-, H- and K-antigens.

Antibodies, Bacterial↗
PubMed1994

Binding studies of a monoclonal antibody specific for 3-deoxy-D-manno-octulosonic acid with a panel of Klebsiella pneumoniae lipopolysaccharides representing all of the O serotypes.

A monoclonal antibody (MAb) raised against Salmonella minnesota R595 and specific for alpha-3-deoxy-D-manno-octulosonic acid (alpha-Kdo) of the inner core was tested for binding to lipopolysaccharides (LPS) of Klebsiella pneumoniae. The MAb was tested in several assay systems (enzyme-linked immunosorbent assay, passive hemolysis, and inhibition of passive hemolysis) with a large panel (n = 23) of K. pneumoniae LPS representing all nine currently known O serotypes. MAb 20 showed reactivity with almost all O serotypes of K. pneumoniae LPS, and this reactivity could be inhibited by synthetic Kdo. This suggests an epitope in the cores of these Klebsiella LPS much like that in the inner core of LPS of S. minnesota. Large differences in reactivity between LPS of different strains belonging to the same O serotype were observed. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis of LPS followed by immunoblotting, reactivity of MAb 20 was observed only with the fast-moving fraction possibly representing the nonsubstituted core. No binding was seen with the high-molecular-weight fraction that contained core material substituted with several units of O-antigen building blocks. The chemical basis for these differences in reactivity remains to be established. As far as we know, this is the first report containing comprehensive immunochemical data on the LPS core of K. pneumoniae.

Antibodies, Monoclonal↗
PubMed1994

Lactoferrin is a lipid A-binding protein.

Lactoferrin (LF), a cationic 80-kDa protein present in polymorphonuclear leukocytes and in mucosal secretions, is known to have antibacterial effects on gram-negative bacteria, with a concomitant release of lipopolysaccharides (LPS, endotoxin). In addition, LF is known to decrease LPS-induced cytokine release by monocytes and LPS priming of polymorphonuclear leukocytes. Its mechanism of action is incompletely understood. We have now demonstrated by in vitro-binding studies that LF binds directly to isolated lipid A and intact LPS of clinically relevant serotypes of the species which most frequently cause bacteremia (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa), as well as to lipid A and LPS of mucosal pathogens (among others, Neisseria meningitides and Haemophilus influenzae). Binding to LPS was inhibitable by lipid A and polymyxin B but not by KDO (3-deoxy-D-manno-octulosonate), a glycoside residue present in the inner core of LPS. Binding of LF to lipid A was saturable, and an affinity constant of 2 x 10(9) M-1 was calculated for the LF-lipid A interaction. Our data may explain, in part, the mechanism whereby LF exerts its antibacterial and anti-endotoxic effects. Further studies on the ability of LF to block the detrimental effects of LPS, both in vitro and in vivo, are warranted.

Carrier Proteins↗
PubMed1994

Recombinant human bactericidal/permeability-increasing protein (rBPI23) is a universal lipopolysaccharide-binding ligand.

A recombinant 23-kDa protein (rBPI23) derived from human bactericidal/permeability-increasing protein (BPI) possesses potent endotoxin-neutralizing abilities in vitro and in vivo. Binding of rBPI23 to those endotoxins (lipopolysaccharides [LPSs]) encountered clinically would be a prerequisite for efficacy in decreasing mortality among patients suffering from gram-negative sepsis and shock, a disease state in which an etiological role for LPS has been implicated. rBPI23 binds well to lipid A (n = 7), to rough-mutant O-chain-deficient LPS (n = 18, Re to Ra chemotypes), to lipid A-core covalently linked to the O chain, to LPSs from clinically relevant serotypes (n = 100), and to bacterial cells (n = 88) of Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae, the species most often implicated in clinical gram-negative sepsis and shock. Significant binding of rBPI23 to these antigens took place at rBPI23 concentrations of 1 to 500 ng/ml (median, 16 to 32 ng/ml). Binding did not involve 3-deoxy-D-manno-octulosonate of the inner core. Determining the exact epitope recognized by rBPI23 would require further studies with synthetic lipid A substructures. The demonstrated ability of rBPI23 to universally bind LPS provides a sound basis for further testing of its endotoxin-neutralizing abilities, including clinical trials.

Antibodies, Monoclonal↗
PubMed1994

Direct PCR enables detection of Mycoplasma pneumoniae in patients with respiratory tract infections.

The sensitivities of three methods of detection of Mycoplasma pneumoniae by a 16S rDNA PCR were compared by using a serial dilution of M. pneumoniae. These methods consisted of a PCR performed directly on cells after a proteinase K pretreatment (direct PCR), a PCR after purification of nucleic acids (DNA-PCR), and a PCR with rRNA sequences as the target after reverse transcription. The direct PCR and the reverse transcription PCR had a sensitivity of 1.5 CFU (approximately 250 genomes). By purification, a 10-fold loss of target DNA occurred, as shown by a 10-fold decrease in sensitivity (15 CFU) of the DNA-PCR. The presence of an excess of human background DNA did not influence the sensitivity of either PCR. The direct PCR was evaluated on samples from patients with respiratory complaints. Direct PCR amplification was possible in 94.9% of the samples, which were tested by amplification of a 326-bp fragment of the beta-globin gene, which was performed to test for the suitability of amplification. Nucleic acid purification was performed on the beta-globin-negative samples, after which only 2% remained negative. A positive correlation between the direct M. pneumoniae PCR and serology, as tested by the microparticle agglutination assay (MAG assay), was found in 88.1% of the cases. A positive MAG assay result was found for samples from 10 (17%) of the patients; samples from 6 (10.2%) of these patients were also positive by PCR. Samples from three patients were found to be positive by the M. pneumoniae PCR and negative by the MAG assay. Persistence of M. pneumoniae, as detected by PCR was observed in three patients. These results indicate that the direct PCR with 16S rDNA could prove to be useful in the detection of M. pneumoniae in respiratory tract samples, although more studies are needed to evaluate the correlation between clinical symptoms and positive test results.

Adolescent↗