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Biomedical subjects

I S Roberts

Publications and source records attributed to I S Roberts.

At least 55 records · Page 3Linked to original sources
PubMed1997

Physiological and biochemical studies on psychrotolerance in Listeria monocytogenes.

Studies were undertaken to explain the ability of Listeria monocytogenes to grow at low temperatures in a chemostat. It was found that when grown in continuous culture at a dilution rate of 0.02 h-1 L. monocytogenes had a lower proportion of anteiso-17:0, and a higher proportion of anteiso-15:0, and smaller chain fatty acids when grown at 10 degrees C compared to 30 degrees C. A previously unreported glycolipid was only seen after growth at low temperature. Growth temperature had no effect on the rate of glucose uptake.

Antimetabolites↗
PubMed1997

Regulation of the Escherichia coli K5 capsule gene cluster by transcription antitermination.

The expression of the Escherichia coli K5 (group II) capsular polysaccharide requires the rfaH gene. By reverse transcriptase-polymerase chain reaction (RT-PCR) it was possible to demonstrate that RfaH increases the transcription of region 2 genes by readthrough transcription from the region 3 promoter. A mutation in the rfaH gene reduced this readthrough transcription from the region 3 promoter by 10-fold as measured by quantitative RT-PCR. The region 3 promoter was mapped to 741 bp 5' of the initiation codon of the kpsM gene. Deletion and insertion mutagenesis of the JUMPstart sequence, which is 28 bp 5' of kpsM and is conserved upstream of RfaH-regulated operons and other polysaccharide biosynthesis genes, confirmed that this sequence was required for expression of the K5 antigen and for the antitermination activity of RfaH. The JUMPstart sequence could cause RfaH-dependent antitermination at other Rho-dependent terminators, suggesting that the JUMPstart sequence may function in a manner analogous to a lambda nut site. On the basis of these results we propose a model by which RfaH regulates expression of E. coli group II capsule gene clusters by allowing readthrough transcription to proceed from region 3 into region 2 and that sequences within the JUMPstart sequence are essential for this process.

Antigens, Bacterial↗
PubMed1997

Interstitial myofibroblasts: predictors of progression in membranous nephropathy.

AIMS: To determine the role of interstitial myofibroblasts in the progression of membranous nephropathy; and to assess the predictive value of quantifying myofibroblasts in determining long term renal outcome. METHODS: All cases of membranous nephropathy, diagnosed by renal biopsy at University Hospital of South Manchester between 1984 and 1987, were studied retrospectively. The biopsy specimens (n = 26) were reviewed and analysed morphometrically to measure interstitial volume as a proportion of the total volume of renal cortex, and numbers of interstitial myofibroblasts (cells positive for alpha-smooth muscle actin within the interstitium). Clinical data, with a follow up of seven to eight years, was available for 24 patients, and renal outcome was correlated with pathological changes in the initial diagnostic biopsy specimen. RESULTS: The number of myofibroblasts and interstitial volume were inversely correlated with creatinine clearance at the initial biopsy, and at the end of follow up. Percentage sclerosed glomeruli or stage of glomerular disease, assessed by electron microscopy, did not correlate with renal function at initial biopsy or during follow up. The number of myofibroblasts, but not interstitial volume, correlated with severity of proteinuria at initial biopsy. Of 15 biopsy specimens showing no or mild interstitial fibrosis, four showed a notable increase in the number of interstitial myofibroblasts. All of these patients developed chronic renal failure, compared with three of 11 patients whose specimens showed no or a mild increase in myofibroblast numbers. CONCLUSIONS: Interstitial myofibroblasts play a role in the development of interstitial fibrosis and progressive renal failure in membranous nephropathy. Increased numbers of myofibroblasts in biopsy specimens showing only mild fibrosis may predict subsequent chronic renal failure.

Actins↗
PubMed1996

Prevention of chronic rejection by donor-specific blood transfusion in a new model of chronic cardiac allograft rejection.

Chronic graft rejection is now a major barrier to the long-term survival of cardiac transplants. A major hallmark of chronic rejection is intimal thickening of arteries in the graft leading to vascular occlusion. Current animal models of chronic rejection generally utilize immunosuppression to prevent acute rejection of grafts disparate at major histocompatibility antigens or graft disparities involving minor histocompatibility antigens alone. In the present communication we describe a new model of chronic rejection involving grafting of PVG-R23 hearts into PVG-RT1(u) recipients. The R23 hearts, which differ from the RT1(u) recipients at class II MHC, are rejected with a chronic time course and demonstrate extensive severe vascular myointimal proliferation within the coronary arteries. Furthermore we demonstrate for the first time that donor-specific blood transfusion can prevent chronic rejection and the intimal thickening of the coronary arteries.

Animals↗
PubMed1996

Response of Mycobacterium smegmatis to acid stress.

Evidence was sought for the existence of an inducible acid tolerance response in Mycobacterium smegmatis. Exposure of M. smegmatis to a sub-lethal, adaptive acidic pH was found to confer a significant level of protection against subsequent exposure to a lethal pH, compared to unadapted cells. Adaptation was dependent on de novo protein synthesis.

Acids↗
PubMed1996

Transcriptional organization and regulation of expression of region 1 of the Escherichia coli K5 capsule gene cluster.

The transcriptional organization and regulation of region 1 expression of the Escherichia coli K5 capsule gene cluster were studied. Region 1 was transcribed as an 8.0-kb polycistronic mRNA which was processed to form a separate 1.3-kb transcript encoding the 3'-most gene kpsS. Transcription of region 1 of the E. coli K5 capsule gene cluster was directed from a single promoter 225 bp upstream of a previously unidentified gene, kpsF. The promoter had -35 and -10 consensus sequences typical of an E. coli sigma 70 promoter, with no similarities to binding sites for other sigma factors. Two integration host factor (IHF) binding site consensus sequences were identified 110 bp upstream and 130 bp downstream of the transcription start site. In addition, two AT-rich regions separated by 16 bp identified upstream of the region 1 promoter were conserved upstream of the region 3 promoter. The kpsF gene was 98.8% identical with the kpsF gene identified in the E. coli K1 antigen gene cluster and confirms that the kpsF gene is conserved among group II capsule gene clusters. An intragenic Rho-dependent transcriptional terminator was discovered within the kpsF gene. No essential role for KpsF in the expression of the K5 antigen could be established. The temperature regulation of region 1 expression was at the level of transcription, with no transcription detectable in cells grown at 18 degrees C. Mutations in regulatory genes known to control temperature-dependent expression of a number of virulence genes had no effect on the temperature regulation of region 1 expression. Likewise, RfaH, which is known to regulate expression of E. coli group II capsules had no effect on the expression of region 1. Mutations in the himA and himD genes which encode the subunits of the IHF led to a fivefold reduction in the expression of KpsE at 37 degrees C, confirming a regulatory role for IHF in the expression of region 1 genes.

Bacterial Capsules↗
PubMed1996

The biochemistry and genetics of capsular polysaccharide production in bacteria.

Bacterial polysaccharides are usually associated with the outer surface of the bacterium. They can form an amorphous layer of extracellular polysaccharide (EPS) surrounding the cell that may be further organized into a distinct structure termed a capsule. Additional polysaccharide molecules such as lipopolysaccharide (LPS) or lipooligosaccharide (LOS) may also decorate the cell surface. Polysaccharide capsules may mediate a number of biological processes, including invasive infections of human beings. Discussed here are the genetics and biochemistry of selected bacterial capsular polysaccharides and the basis of capsule diversity but not the genetics and biochemistry of LPS biosynthesis (for reviews see 100, 140).

Antigens, Bacterial↗
PubMed1996

Complete clinical remission and subsequent relapse of bronchiectasis-related (AA) amyloid induced nephrotic syndrome.

Systemic amyloidosis normally has a dismal prognosis. However, there are several case reports of protracted survival, usually as a response to measures designed to retard the further deposition of amyloid fibrils. In AA amyloid, most commonly associated with inflammatory rheumatological, bowel, and chest diseases, such interventions have had some success, but the dramatic response of complete resolution of nephrotic syndrome as a result of the regular institution of postural chest drainage and antibiotic therapy, in the clinical context of bronchiectasis, has been previously reported only once. In both of our cases, after protracted remission, such therapy was abandoned by the patients, leading both to recurrence of nephrotic syndrome and also eventually to end-stage renal failure requiring dialysis.

Adult↗
PubMed1995

Isolation from recombinant Escherichia coli and characterization of CMP-Kdo synthetase, involved in the expression of the capsular K5 polysaccharide (K-CKS).

In Escherichia coli with group II capsules, the synthesis of capsular polysaccharide and its cellular expression are encoded by the kps gene cluster, which is composed of three regions. The central region 2 encodes proteins involved in polysaccharide synthesis, and the flanking regions 1 and 3 direct the translocation of the finished polysaccharide across the cytoplasmic membrane and its surface expression. The kps genes of E. coli with the group II capsular K5 polysaccharide, have been cloned and sequenced. Region 1 contains the kpsE, D, U, C and S genes. In this communication we describe the overexpression of the kpsD and kpsU genes as well as the isolation of the KpsU protein from the recombinant bacteria by chloroform treatment. The purified KpsU protein exhibited CMP-Kdo-synthetase activity. The N-terminal sequence and two internal peptide sequences of the isolated protein are in agreement with that previously predicted from the DNA sequence of the kpsU gene. The kinetic data of the CMP-Kdo-synthetase participating in K5 capsule expression (K-CMP-Kdo-synthetase) differ from those described for the CMP-Kdo-synthetase, participating in lipopolysaccharide synthesis (L-CMP-Kdo-synthetase).

Amino Acid Sequence↗
PubMed1995

Comparative study of the growth of Listeria monocytogenes in defined media and demonstration of growth in continuous culture.

A basic requirement for physiological studies with Listeria monocytogenes is a chemically defined medium that supports growth of the bacterium in batch and continuous culture. A number of such media have been devised but comparative studies of their efficiency are few and none has been used in continuous culture. Six of the media were compared for their ability to sustain sequential growth of L. monocytogenes in static and aerated batch culture with glucose as sole carbon source. The most suitable, judged on the basis of ease of preparation, growth rate and yield, was that of Trivett and Meyer (1971). This medium was shown to support growth of L. monocytogenes NCTC 7973 in continuous culture in a chemostat. A lytic phenomenon, noted with the same strain under anaerobic conditions and in batch culture in the chemostat, is discussed.

Aerobiosis↗
PubMed1995

Region 2 of the Escherichia coli K5 capsule gene cluster encoding proteins for the biosynthesis of the K5 polysaccharide.

The nucleotide sequence of region 2 of the Escherichia coli K5 capsule gene cluster has been determined. This region, essential for the biosynthesis of the K5 polysaccharide, contained four genes, termed kfiA-D. The G + C ratio was 33.4%, which was lower than the typical G + C ratio for E. coli and that of the flanking regions 1 and 3 in the K5 capsule gene cluster. Three major RNA transcripts were detected within region 2 by Northern blotting and three promoters located by transcript mapping. Promoter activity was confirmed by promoter-probe analysis. The predicted amino acid sequence of KfiC had homology to a number of glycosyl transferase enzymes and overexpression of the KfiC gene resulted in increased K5 transferase activity. The predicted amino acid sequence of KfiD had homology to a number of NAD-dependent dehydrogenase enzymes and was demonstrated to be a UDP-glucose dehydrogenase that catalyses the information of UDP-glucuronic acid from UDP-glucose.

Amino Acid Sequence↗
PubMed1995

Cloning and analysis of gene clusters for production of the Escherichia coli K10 and K54 antigens: identification of a new group of serA-linked capsule gene clusters.

The polysaccharide capsules of Escherichia coli have been classified into three groups: I, II, and I/II. The third group, I/II, has been poorly studied and possesses characteristics of both group I and group II capsules. In this report, we describe the cloning of the K10 and K54 capsule gene clusters, two representatives of group I/II capsules. Probes taken from DNA flanking regions 1 and 3 of the group II capsule clusters hybridized to these group I/II clones, confirming that the group I/II capsule genes are flanked by the same DNA and are therefore located in the same serA-linked region of the chromosome as group II capsule gene clusters. Southern blotting showed that homologous sequences were present in both the K10 and K54 capsule gene clusters and in other group I/II strains. No homology was detected between these sequences and the chromosomal DNA of either a group I or a group II strain. Likewise, no homology was detected to the chromosomal DNA of either a K11 or K19 strain, both of which had previously been classified as group I/II strains. In the K10 and K54 capsule gene clusters, these conserved sequences flanked a serotype-specific region in a manner analogous to group II capsule gene organization. Complementation of mutations in the kpsE, kpsD, and kpsC genes in region 1 of the K5 capsule gene cluster by subclones of the K10 and K54 capsule gene clusters indicated that certain stages in the export of group II and I/II capsules may be conserved. In the light of the findings presented here, we suggest that the group I/II capsule gene clusters are sufficiently different from group II capsule gene clusters to justify their renaming as group III.

Antigens, Bacterial↗