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Biomedical subjects

S Tabaqchali

Publications and source records attributed to S Tabaqchali.

At least 55 records · Page 3Linked to original sources
PubMed1991

Epidemiology of CAPD-associated peritonitis caused by coagulase-negative staphylococci: comparison of strains isolated from hands, abdominal Tenckhoff catheter exit site and peritoneal fluid.

We identified twenty patients maintained on continuous ambulatory peritoneal dialysis who suffered repeated episodes of peritonitis caused by coagulase-negative staphylococci. We documented hand and exist-site coagulase-negative staphylococcus-associated peritonitis over a total period of 32 months, and compared hand and exit-site strains with strains isolated from dialysate fluid using three typing methods: biotyping using the API Staph kit plus antibiograms, immunoblotting using sera raised in rabbits to three standard strains of coagulase-negative staphylococci, and 35S-methionine-labelled coagulase-negative staphylococcal profiles separated on sodium dodecylsulphate polyacrylamide gel electrophoresis and visualised by autoradiography (radioPAGE). In 5 of 84 episodes, strains isolated from skin were indistinguishable by all three typing methods from the dialysate strain. In a further two episodes, hand or exit-site isolates were indistinguishable by all three typing methods from the dialysate strain isolated in the subsequent, but not the same, episode. Thus in the majority of episodes, no inference of hand or exit-site origin of dialysate infection could be drawn.

Adult↗
PubMed1991

Histidine decarboxylases from bacteria that colonise the human respiratory tract.

We investigated whether production of histamine by bacteria isolated from sputum of patients with infective lung diseases could be attributed to the presence of histidine decarboxylase (HD). Twenty gram-positive and 20 gram-negative organisms were studied for their ability to decarboxylate 14C-histidine in vitro over the pH range 4.5-7.5. Of the bacteria investigated, lysates from the gram-negative species Haemophilus influenzae, H. parainfluenzae, Moraxella (Branhamella) catarrhalis and Pseudomonas aeruginosa liberated 14CO2 and histamine from 14C-histidine in the presence of the cofactor pyridoxal phosphate. In contrast, results obtained in the absence of cofactor were similar to those of negative (lysate-free) controls suggesting that the HD enzymes of these species resembled those previously described in other gram-negative bacteria. No HD activity was detected over this pH range in lysates from gram-positive species. This finding correlated with earlier observations that these gram-positive organisms did not produce histamine in vitro.

Carbon Dioxide↗
PubMed1991

Characterization of a plasmid from Helicobacter pylori encoding a replication protein common to plasmids in gram-positive bacteria.

A 1.5 kb cryptic plasmid was isolated from Helicobacter pylori. Low-stringency hybridization analysis using this plasmid as a DNA probe revealed base sequence homology with other plasmids in this species. Nucleotide sequence analysis identified an open reading frame encoding a putative polypeptide of 25 kDa. This protein showed marked amino acid sequence similarity to replication-initiation proteins commonly found in small plasmids endogenous to Gram-positive bacteria which replicate by the 'rolling-circle' mechanism. Sequence motifs corresponding to the origins-of-replication consensus sequences were found on this cryptic plasmid. DNA and oligonucleotide probes to these plasmid replication sequences were used in hybridization analysis to identify similar sequences in other H. pylori plasmids. We believe this is the first plasmid isolated from a Gram-negative bacterium to show replication determinants characteristic of the 'rolling-circle' group of plasmids from Gram-positive bacteria. The cloned plasmid will be used to develop a shuttle-vector for H. pylori.

Amino Acid Sequence↗
PubMed1991

Antigenic cross-reactivity and functional inhibition by antibodies to Clostridium difficile toxin A, Streptococcus mutans glucan-binding protein, and a synthetic peptide.

A 10-amino-acid repeating sequence of the hemagglutinating portion of Clostridium difficile toxin A has been synthesized and used to produce antisera in rabbits. Antipeptide antibody inhibited toxin A-mediated hemagglutination and neutralized cytotoxic activity. Immunoblot analysis with the antipeptide antibody revealed cross-reactivity with native toxin, a recombinant protein containing the toxin A repeats, and a glucan-binding protein from Streptococcus mutans whose primary structure has repeating amino acid motifs similar to those of the synthetic peptide. A polyclonal antibody against the glucan-binding protein, which cross-reacted with purified toxin A, also inhibited toxin A-mediated hemagglutination and neutralized cytotoxic activity. We recently identified toxin A and the glucan-binding protein as members of a novel family of clostridial and streptococcal binding proteins based on conserved repeating amino acid motifs at the C-terminal region of the molecules. This study provides immunological and functional evidence of the predicted relationship between toxin A and the glucan-binding protein and further implicates the repeating subunits as ligand-binding domains in this family of proteins.

Amino Acid Sequence↗
PubMed1991

Mycobacterium paratuberculosis and Crohn's disease.

The possible aetiological role of Mycobacterium paratuberculosis in Crohn's disease was investigated. The immunological response was studied using an enzyme-linked immunosorbent assay (ELISA), Western blotting, and immunocytochemistry. The antibody response to two protoplasmic antigen preparations of M paratuberculosis in the sera of patients with inflammatory bowel disease was measured by ELISA. IgG and IgM antibodies to these antigens were measured in serum samples from 52 patients with Crohn's disease, 15 patients with ulcerative colitis, and 41 control patients without inflammatory bowel disease. Although there was wide variation in the concentrations of antibody detected, patients with Crohn's disease had concentrations that were not significantly different from those of the other two groups. In addition, mycobacterial antigens were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and the immune response to each antigen was then examined separately and assayed for IgG and IgM in 10 patients from each of the three groups. An indirect peroxidase test was also used to detect M paratuberculosis in sections of tissue from 18 patients with Crohn's disease and 10 with ulcerative colitis. The results were negative in all cases. This study does not support a role for M paratuberculosis in Crohn's disease.

Adolescent↗
PubMed1991

Diagnostic efficiency of an ultrarapid endoscopy room test for Helicobacter pylori.

There are several reliable methods for detecting Helicobacter pylori but all have as a major disadvantage the time required to yield a definitive result. We have modified the standard urease test so that a positive result is available in one minute. We describe the use of this test in biopsy specimens from the gastric antrum from 220 consecutive patients referred for upper gastrointestinal endoscopy. The performance of the 'one minute test' was compared with a standard urease test, Gram stain, and microbiological culture. Using culture as the 'gold standard' 80 (36%) of the patients were H pylori positive. The one minute test produced no false positives and showed a sensitivity of 89% and specificity of 100%, while the predictive values of a positive and negative test were 100% and 94% respectively. The diagnostic efficiency of the test was 96% compared to 85% for both the Gram stain and direct urease test. All positive results using the one minute test were available within one minute. The test is easy to prepare and costs approximately pounds 0.04. This new modification of the urease test should be superior to the currently available urease tests because a reliable result will be available in almost 90% of infected individuals even before endoscopy is completed.

Adult↗
PubMed1991

Detection and identification of Helicobacter pylori by the polymerase chain reaction.

A polymerase chain reaction for the specific detection of Helicobacter pylori was developed using a primer pair derived from the nucleotide sequence of the urease A gene of H pylori. Specific amplification of a 411 base pair DNA fragment from all strains of H pylori tested was achieved. Ten organisms were detected using the PCR and the technique permitted direct detection of H pylori in clinical biopsy samples. PCR will be useful for both prospective and retrospective investigation of the aetiology and epidemiology of H pylori associated disease.

Base Sequence↗
PubMed1990

Nucleotide sequence of Clostridium difficile toxin A gene fragment and detection of toxigenic strains by polymerase chain reaction.

A 1947 base pair (bp) fragment of the toxin A gene of Clostridium difficile was sequenced. A continuous open reading frame was found, which contained 4 distinct groups of repeat nucleotide sequence with 88 to 100% identity within each group. The arrangement of the groups (A, 81 bp, B, C and D, 63 bp) was ABCCCDABCDDABCCCDABCCDABCDABC. Based on nucleotide sequence data from the C repeat group, a pair of oligonucleotide primers were synthesised and used in the polymerase chain reaction (PCR) to amplify fragments from the toxin A gene. Several products of multiples of 63 bp length were amplified for all 33 toxigenic C. difficile strains tested in contrast to the 12 non-toxigenic strains tested which failed to amplify any product. This rapid technique is of potential use in the specific identification of toxigenic C. difficile strains in mixed culture and from clinical specimens.

Amino Acid Sequence↗
PubMed1990

Effect of ceftazidime and gentamicin on the oropharyngeal and faecal flora of patients with haematological malignancies.

Thirty-four patients with haematological malignancies were studied to investigate the effect of empirical broad-spectrum antibiotic therapy (ceftazidime and gentamicin) on the gastro-intestinal flora. Twenty-five patients with acute myeloid leukaemia or post-autologous bone-marrow transplantation were given framycetin, nystatin and colistin (Fracon), and two patients with non-Hodgkin's Lymphoma were on co-trimoxazole, as long-term gut prophylaxis. Semi-quantitative microbiology was carried out on oropharyngeal swabs and quantitative microbiology on faecal specimens. The oropharyngeal flora consisted mainly of streptococci, coagulase-negative staphylococci and coryneforms, and was little affected by ceftazidime/gentamicin. A strain of Enterobacter cloacae resistant to ceftazidime and gentamicin colonized one patient, who later developed septicaemia. The faecal flora of patients on Fracon was dominated by enterococci; the few enterobacteria present were eliminated by ceftazidime/gentamicin. The anaerobic flora was absent in 15% of patients; in the remainder, it consisted mainly of Bacteroides spp., and was little affected by ceftazidime/gentamicin. The faecal flora of patients not on Fracon always contained anaerobes, and some strains of enterobacteria persisted throughout antibiotic treatment. None of the patients was colonized by Clostridium difficile or Pseudomonas aeruginosa. Broad-spectrum therapy with ceftazidime and gentamicin appeared to have little effect on the gastro-intestinal flora, except to encourage the overgrowth of enterococci and reduce the numbers of enterobacteria.

Ceftazidime↗
PubMed1990

Genetic analysis of a tetracycline resistance element from Clostridium difficile and its conjugal transfer to and from Bacillus subtilis.

A tetracycline resistance (Tcr) determinant from Clostridium difficile strain 630 was cloned into the Escherichia coli plasmid vector pUC13. The resulting plasmid pPPM20, containing an insert of 3.4 kbp, was mapped and a 1.1 kbp SacI-HindIII fragment wholly within the Tcr gene was identified. Dot-blot hybridization studies with the 1.1 kbp fragment showed that the Tcr gene belonged to hybridization class M. Tcr could be transferred between C. difficile strains and to Bacillus subtilis at a frequency of 10(-7) per donor cell. The element could be returned from B. subtilis to C. difficile at a frequency of 10(-8) per donor cell. This is the first demonstration of C. difficile acting as a recipient in intergeneric crosses. DNA from C. difficile transconjugants digested with EcoRV always has two hybridizing fragments of 9.5 and 11.0 kbp when probed with pPPM20. DNA from B. subtilis transconjugants digested with EcoRV produced one hybridizing band of variable size when probed with pPPM20. The behaviour of the element was reminiscent of the conjugative transposons. Therefore we compared the element to the conjugative transposon Tn916. The HincII restriction maps of the two elements differed and no hybridization was detected to oligonucleotides directed to the ends of Tn916. However, the elements do have some sequence homology, detected by hybridization analysis.

Bacillus subtilis↗
PubMed1990

Identification of toxigenic Clostridium difficile strains by using a toxin A gene-specific probe.

A 4.5-kilobase PstI fragment encoding part of the toxin A gene was isolated and used as a DNA probe in colony hybridization studies with 58 toxigenic and 17 nontoxigenic Clostridium difficile strains. All 58 toxigenic strains showed positive hybridization, in contrast to the 17 nontoxigenic strains. Southern blot analysis with the toxin A gene probe showed hybridization to a single fragment of equal intensities for HindIII-digested genomic DNAs isolated from C. difficile strains of wide-ranging toxin production. The positive hybridization signals were due to fragments of heterogeneous lengths (9 to 13 kilobases) for toxigenic strains of different types but were absent for the nontoxigenic strains. These results suggest the presence of a single copy of the toxin A gene on the genome of C. difficile strains, and the wide variation of toxin expression is not a reflection of gene copy number. The lack of toxin activity for nontoxigenic strains can be explained by the absence of at least part of the toxin A gene. The toxin A gene probe was tested against clostridial strains from 18 other species, of which only toxigenic C. sordellii strains showed positive hybridization. The specificity of the toxin A gene probe for toxigenic strains may lead to improved methods for the specific identification of toxigenic C. difficile strains from clinical specimens.

Bacterial Toxins↗