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Biomedical subjects

J R Scott

Publications and source records attributed to J R Scott.

At least 145 records · Page 8Linked to original sources
PubMed1991

A host factor absent from Lactococcus lactis subspecies lactis MG1363 is required for conjugative transposition.

In matings between Lactococcus lactis strains, the conjugative transposons Tn916 and Tn919 are found in the chromosome of the transconjugants in the same place as in the chromosome of the donor, indicating that no transposition has occurred. In agreement with this, the frequency of L. lactis transconjugants from intraspecies matings is the same whether the donor contains the wild-type form of the transposon or the mutant Tn916-int1, which has an insertion in the transposon's integrase gene. However, in intergeneric crosses with Bacillus subtilis or Enterococcus faecalis donors, Tn916 and Tn919 transpose to different locations on the chromosome of the L. lactis transconjugants. Moreover, Tn916 and Tn919 could not be transferred by conjugation from L. lactis and B. subtilis, E. faecalis or Streptococcus pyogenes. This suggests that excision of these elements does not occur in L. lactis. When cloned into E. coli with adjacent chromosomal DNA from L. lactis, the conjugative transposons were able to excise, transpose and promote conjugation. Therefore, the inability of these elements to excise in L. lactis is not caused by a permanent structural alteration in the transposon. We conclude that L. lactis lacks a factor required for excision of conjugative transposons.

Bacillus subtilis↗
PubMed1991

Analysis of peripheral leucocyte populations in N'Dama and Boran cattle following a rechallenge infection with Trypanosoma congolense.

Monoclonal antibodies, flow cytometry and routine haematological techniques were used to analyse circulating leucocyte populations in trypanotolerant (N'Dama) and trypanosusceptible (Boran) cattle following a homologous rechallenge with Trypanosoma congolense clone IL13-E3. The N'Damas developed a low, transient parasitaemia and did not develop anaemia. The Borans became parasitaemic and developed chronic anaemia but three of the five animals eventually self-cured, whilst, a group of primary-challenged Borans experienced a severe infection characterized by high levels of parasitaemia and acute anaemia. During infection the numbers of circulating B-cells increased in all three groups from day 21 onwards. The proportion of B-cells expressing the CD5 antigen increased from pre-infection levels of 5-10% of B-cells to 49-90% by day 19 post infection in all three groups. The neutrophil count declined in both Boran groups but not in the N'Damas. The CD4+ T-cell and gamma delta T-cell populations decreased in both Boran groups but did not alter significantly in the N'Damas. Although it was not possible to infer from the data, that the CD4+, gamma delta T-cell, neutrophil and erythrocyte populations were directly responsible for the differential control of the disease by the two breeds, it was possible to correlate alterations in these cell populations with the severity of the disease.

Animals↗
PubMed1991

Susceptibility of N'Dama and Boran cattle to tsetse-transmitted primary and rechallenge infections with a homologous serodeme of Trypanosoma congolense.

Eight trypanotolerant N'Dama cattle controlled an infection of Trypanosoma congolense ILNat 3.1 transmitted by Glossina morsitans centralis, more efficiently than a group of similarly infected trypanosusceptible Boran cattle. All eight N'Damas maintained their PCV above 15% throughout the primary infection whereas the PCV of six of the eight Borans dropped below 15%; these latter animals were treated with diminazene aceturate to prevent possible death. Lymphocyte, neutrophil and platelet counts also decreased in the Boran during the primary infection. In contrast, a lymphocytosis was observed in the N'Dama; and although the neutrophil and platelet counts decreased, the drop was less severe than in the Boran. Two years after the primary infection and immediately prior to a homologous rechallenge infection, all eight N'Damas had neutralizing anti-metacyclic trypanosome variant-specific antibodies present in their sera compared to five of the eight Borans. Following the homologous rechallenge infection the eight N'Damas became parasitaemic but there were no alterations in their erythrocyte or leukocyte counts. The Borans became highly parasitaemic and developed severe, chronic anaemia and leukopaenia. Thus, the trypanotolerant N'Damas controlled a primary infection of T. congolense more efficiently than trypanosusceptible Boran cattle and eliminated a homologous rechallenge infection without the pathology associated with the disease.

Animals↗
PubMed1991

Susceptibility of N'Dama and Boran cattle to sequential challenges with tsetse-transmitted clones of Trypanosoma congolense.

The susceptibility of N'Dama cattle (Bos taurus) to four consecutive infections with different tsetse-transmitted clones of Trypanosoma congolense was compared with that of Borans (Bos indicus). All animals were aged 13 months at the start of the study and had been born and raised free from trypanosomiasis under the same management and nutritional conditions, thereby limiting environmental factors that could have influenced susceptibility. While cattle of both breeds were equally susceptible to the establishment of trypanosome infections, the N'Damas exhibited superior resistance. Despite infection with virulent parasites, the N'Damas gained weight at the same rate as uninfected control animals, they did not develop anaemia to the extent that trypanocidal drug treatment was required, and all made a spontaneous recovery to normal haematological values within two to four months. In contrast, all the Borans needed treatment during the course of the four infections because of severe anaemia and showed markedly reduced liveweight gains. These clinical differences in the N'Damas were associated with two repeatable characteristics, namely, the ability to control parasitaemia and to 'resist' anaemia, processes that did not appear to be linked. Also in contrast to the Borans, the N'Damas were able to mount accelerated haemopoietic responses, resulting in the reduced severity of anaemia following a primary infection. These findings pose the question as to whether the ability to control parasitaemia and to 'resist' anaemia could be used as criteria for identifying resistant or trypanotolerant cattle.

Anemia↗
PubMed1991

Role of M protein in adherence of group A streptococci.

The role of the M protein in adherence of group A streptococci to human epithelial cells was directly tested by using an isogenic pair of M+ and M- strains. There was no difference between these strains in the number of streptococcal units that adhered to buccal or tonsillar epithelial cells, indicating the following: (i) that adhesins that are not dependent upon M protein expression are present on the surface of group A streptococci and (ii) that the M protein is not the primary streptococcal adherence ligand. However, the M+ strain adhered to tonsillar epithelial cells as aggregates. This aggregation was dependent on the presence of the M protein, since the isogenic M- strain did not clump. The coaggregation of streptococci suggests that the M protein plays an important role in promoting the formation of microcolonies after initial attachment. Binding to fibronectin, a potential epithelial cell receptor for group A streptococci, was also the same for the isogenic M+ and M- strains as well as for an isogenic strain with a regulatory mutation that decreases the expression of M protein. In summary, the M protein is not the primary streptococcal adhesin, nor is it required to orient the streptococcal adhesin and/or fibronectin receptor.

Antigens, Bacterial↗
PubMed1991

The presence of conjugative transposon Tn916 in the recipient strain does not impede transfer of a second copy of the element.

Transfer of the conjugative transposon Tn916 from the chromosome of Bacillus subtilis to a transposon-free Streptococcus pyogenes strain occurs at the same frequency as transfer to a Tn916-containing recipient. This rules out a model for conjugal transfer of Tn916 in which a copy of the element in the recipient represses transposition of a copy introduced by conjugation. Homology-directed integration of the incoming transposon into the resident one is less frequent than insertion elsewhere in the chromosome. This shows that after conjugation, transposition occurs more frequently than homologous recombination. However, because transconjugants arising from homologous recombination can be selected, it is possible to use Tn916 as a shuttle for gram-positive organisms for which there is no easy means of introducing DNA.

Bacillus subtilis↗
PubMed1991

Mry, a trans-acting positive regulator of the M protein gene of Streptococcus pyogenes with similarity to the receptor proteins of two-component regulatory systems.

In the Streptococcus pyogenes M6 strain D471, an insertion of the conjugative transposon Tn916 into a region 2 kb upstream of the promoter of emm6 (the structural gene for the M protein) rendered the strain M negative (M. G. Caparon and J. R. Scott, Proc. Natl. Acad. Sci. USA 84:8677-8681, 1987). In the present work, we show that this insertion mutation, mry-1, is 244 bp upstream of an open reading frame encoding a protein we call Mry. This protein is visible on a gel after transcription and translation in vitro. We have developed a technique for complementation analysis in S. pyogenes and have used it to show that the wild-type mry gene is dominant to two mutant alleles. This dominance indicates that Mry acts in trans as a positive regulator of the emm6 gene. The translated DNA sequence of mry has two regions of similarity to the motif common to the receptor protein of two-component regulatory systems. In addition, the N terminus of Mry has two regions resembling a helix-turn-helix motif. Mry does not appear to be a global regulator of virulence determinants in the group A streptococcus because there is no effect of the mry-1 mutation on production of the hyaluronic acid capsule or streptokinase.

Amino Acid Sequence↗
PubMed1991

Intramembranous particle distribution and filipin binding in dysplastic canine retina.

We examined dysplastic canine retina for changes in intramembranous particle (IMP) density and filipin binding to sterols. Differences in IMP density were identified in incipiently dysplastic fetal retina and also in the degree of filipin binding near the onset of the dysplastic process. The data suggest that there are temporal differences in IMPs and filipin-sterol complexes that may be related to the formation of retinal folds and disorganized dysplastic retina proliferation.

Animals↗
PubMed1991

The outcome of pregnancies complicated by bleeding during the second trimester.

Vaginal bleeding during the second trimester has historically been associated with high perinatal mortality rates (33 to 82 per cent). Because this topic has not been specifically studied since the advent of obstetric ultrasound and electronic fetal heart rate monitoring, we reviewed the experience at the University of Utah with second trimester vaginal bleeding from 1 January 1983 through 15 June 1989. The cause of the bleeding was found to fit into four general categories. These are placenta previa, abruption, both previa and abruption, and other or unknown. Midtrimester bleeding is still associated with a high perinatal mortality rate (22.3 per cent), being highest when associated with placental abruption (36.6 per cent) and lowest with placenta previa (7.4 per cent). For the entire series, pregnancies maintained into the third trimester were associated with a much lower perinatal mortality rate than those in which delivery occurred during the second trimester (7.1 versus 54.5 per cent). These relatively improved outcomes suggest that aggressive obstetric management is warranted in most instances.

Abruptio Placentae↗
PubMed1991

Mandatory trial of labor after cesarean delivery: an alternative viewpoint.

Twelve women experienced major rupture of the uterus during a trial of labor after previous cesarean (low transverse cervical incision in 11, low vertical in one). Two women required hysterectomy and a third had serious postoperative complications. There were three perinatal deaths, and two infants suffered significant long-term neurologic impairment. Although vaginal birth after cesarean delivery is considered safe in most instances, these cases serve as a reminder that catastrophic events can occur. Potential complications have important implications for clinicians when counseling patients about the route of delivery and for the management of any trial of labor after cesarean delivery.

Adult↗
PubMed1990

Lectin binding patterns in developing canine retina.

Developing canine retina, fixed in Bouin's or Tellyesnizky's acetic alcoholic formalin, was examined with a battery of biotinylated lectins. ConA and WGA consistently bound to all retinal layers including the tapetum cellulosum, retinal pigment epithelium, inner and outer segments, plexiform layers and ganglion cells. Binding became more intense with increased age. S-WGA bound to apical portions of the retinal pigment epithelium and to outer segments. Outer segments also bound ConA, WGA and RCA. DBA preferentially labelled all inner segments, while PNA bound to a subpopulation of inner segments. RCA bound intensely to retinal vessels as did PNA after neuraminidase treatment. UEA did not consistently bind to any layers. There was transient binding by some lectins at different developmental stages. This study indicates that canine retina demonstrates differential expression of glycoproteins, as indicated by lectin binding, during development and that this expression is temporally and topographically regulated.

Animals↗
PubMed1990

Interpretation of blocking activity in maternal serum depends on the equation used for calculation of mixed lymphocyte culture results.

Immunosuppressive blocking factors in maternal serum are usually determined by inhibition of mixed lymphocyte cultures (MLC), but reports on the importance of these factors for successful pregnancy are conflicting. Here we measured serum blocking activity in men, non-pregnant nulliparous women, non-pregnant multiparous women, women with normal pregnancies, and in women who had had recurrent spontaneous abortions and were treated with leucocyte immunizations. Three different equations were used for calculation of blocking activity: blocking effect index (BEI); stimulation index (SI); and blocking index (BI). By all three methods of calculation, significantly lower levels of blocking activity were noted for men and women compared with pregnant women and multiparae. In the patients with a history of recurrent spontaneous abortions blocking activity as determined by BEI and BI increased into the positive range after treatment with infusions of third-party donor leucocytes in a statistically significant number of women (P less than 0.05). However, blocking activity as determined by BEI had a higher predictive value for successful pregnancy than did that determined by BI or SI. Our data suggest that the equation used for calculating BEI is superior to other methods for the determination of blocking activity when monitoring the response to leucocyte immunization in women with recurrent spontaneous abortion. However, these results also cast doubt on the importance of blocking antibodies in histories of recurrent abortion, since pregnancies occurred in the absence and spontaneous abortions occurred in the presence of blocking activity.

Abortion, Habitual↗
PubMed1990

The use of monosodium glutamate in identifying neuronal populations in mice infected with scrapie.

The excitatory amino-acid, monosodium glutamate, which causes degeneration in the retinal ganglion cells in neonatal mice, was used to investigate the transport of scrapie within optic nerve axons. In treated mice, there was prolongation of the incubation period following intraocular infection with the ME7 strain of scrapie, and a decrease in the severity of retinopathy after intracerebral infection with the 79A strain. These data confirm that scrapie infection spreads along neural pathways, and demonstrate the potential use of selective neurotoxins to study pathogenesis.

Animals↗
PubMed1990

Association of rns homologs with colonization factor antigens in clinical Escherichia coli isolates.

rns is a trans-acting positive regulatory factor required for expression of the colonization factor antigen II (CFA/II) antigens CS1 and CS2 (J. Caron, L. M. Coffield, and J. R. Scott, Proc. Natl. Acad. Sci. USA 86:963-967, 1989). All 35 CFA/II-positive strains hybridized with a rns gene probe, as did all 10 CFA/I strains and all 4 CS4 strains. Hybridization with rns was detected in 25% of non-enterotoxigenic Escherichia coli strains and was not detected in enteric pathogens with low G + C content.

Antigens, Bacterial↗
PubMed1990

Gene encoding the major subunit of CS1 pili of human enterotoxigenic Escherichia coli.

Some enterotoxigenic strains of Escherichia coli (ETEC) utilize the CS1 pilus for colonization of human intestinal epithelium. We have cloned the gene which encodes the major CS1 subunit and called it cooA (for coli surface antigen one). Hybridization showed that the ETEC strain from which it was cloned carried cooA on a plasmid different from the one encoding its positive regulator, rns. Based on the cooA DNA sequence, cleavage with signal peptidase would be expected to produce a mature protein of 15.2 kDa; a 16-kDa polypeptide that reacted with CS1-specific antiserum was observed on electrophoresis. At the protein level, there was 92% similarity and 55% identity between cooA and cfaB, the major colonization factor antigen I (CFA/I) antigen. However, CS1-specific antisera did not react with CfaB. No hybridization was seen between either of two different cooA probes and total DNA from ETEC strains expressing AFA-1, CFA/I, CS2, CS3, CS4, CS5, or CS6.

Amino Acid Sequence↗
PubMed1990

A rns-like regulatory gene for colonization factor antigen I (CFA/I) that controls expression of CFA/I pilin.

Colonization factor antigens (CFA) are needed for adherence of human enterotoxigenic Escherichia coli (ETEC) strains to their hosts. The CFA/II antigens, CS1 and CS2, which are found in some ETEC strains, require the plasmid-encoded gene rns for expression (J. Caron, L. M. Coffield, and J. R. Scott, Proc. Natl. Acad. Sci. USA 86:963-967, 1989). Other ETEC strains express CFA/I, whose synthesis and assembly require genes on two unlinked regions (regions 1 and 2) of a plasmid (G. A. Willshaw, H. R. Smith, and B. Rowe, FEMS Microbiol. Lett. 16:101-106, 1983). We report that CFA/I region 2 DNA can substitute for rns to cause expression of CS1 and CS2. The cfaR gene in region 2 is defined by a mutation abolishing both expression of CFA/I and complementation of a rns mutant for expression of CS1 or CS2. In a strain containing only region 1, complementation for expression of CFA/I by a plasmid containing rns+ is inefficient but is adequate to cause hemagglutination by the CFA/I adhesin.

Antigens, Bacterial↗
PubMed1990

Second-site revertants of the P1 copN22 copy mutant.

Miniplasmids with the P1 copN22 mutation have a copy number about seven times that of the wild type. Selection for reduced copy number from this plasmid led to the isolation of second-site pseudorevertants, called poc mutants. DNA sequence analysis showed that all six independent poc mutants have a single base change in the same codon of the repA gene. This implicates the amino acid at this location, either directly or indirectly, in interactions important for copy number control.

Base Sequence↗