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Biomedical subjects

G R Smith

Publications and source records attributed to G R Smith.

At least 235 records · Page 13Linked to original sources
PubMed1986

The adverse effect of dilution on the infectivity of Fusobacterium necrophorum culture.

Dilution had an adverse effect on the infectivity of 24 h cultures of a strain of Fusobacterium necrophorum, which became apparent at or near the minimum lethal dose. Thus in mice inoculated subcutaneously the mortality produced by 0.01 ml of undiluted culture was almost invariably greater than that produced by 0.1 ml of a 1 in 10 dilution. The explanation appeared to lie in the increased physical separation of bacterial cells that was the inevitable consequence of dilution.

Animals↗
PubMed1986

recD: the gene for an essential third subunit of exonuclease V.

Exonuclease V (EC 3.1.11.5) of Escherichia coli, an enzyme with multiple activities promoting genetic recombination, has previously been shown to contain two polypeptides, the products of the recB and recC genes. We report here that the enzyme contains in addition a third polypeptide (alpha) with a molecular mass of about 58 kDa. The alpha polypeptide is not synthesized by a class of mutants (previously designated recB) lacking the nuclease activity of exonuclease V but retaining recombination proficiency. The gene, recD, coding for the alpha polypeptide is located near recB in the order thyA-recC-ptr-recB-recD-argA on the E. coli chromosome. The recB and recD genes appear to be governed by a common promoter to the left of recB; a weaker promoter appears to govern recD alone. In the light of these results we discuss the relation between the structure and function of the three polypeptides of exonuclease V, hereby alternatively designated RecBCD enzyme.

Bacterial Proteins↗
PubMed1986

Activity of Chi recombinational hotspots in Salmonella typhimurium.

Chi sites have previously been shown to stimulate homologous recombination by the Escherichia coli RecBC pathway. To test the activity of Chi in another organism, bacteriophage lambda crosses were carried out in Salmonella typhimurium strains bearing the E. coli lambda receptor protein. Chi is active in these crosses in S. typhimurium, but is less active than in the same crosses carried out in E. coli. The lower Chi activity in S. typhimurium appears to be intrinsic to the S. typhimurium RecBC enzyme, since the Chi activity in E. coli-S. typhimurium hybrids depends on the species of origin of their RecBC enzyme. For these studies we constructed and F' factor and a pBR322-derived plasmid carrying the thyA+ recC+ recB+ argA+ region of the S. typhimurium chromosome.

Bacteriophage lambda↗
PubMed1986

Nerve root cut-off on metrizamide-enhanced computerized tomography.

The "wink" sign of nerve root cut-off seen on metrizamide-enhanced computerized tomography correlates well with compression of a lumbar nerve by a herniated disk. Seven of 46 patients had normal or equivocal myelograms, but had definite nerve root cut-off on metrizamide-enhanced CT scan. All seven patients were found to have a herniated lumbar disk at operation or a diskogram positive for herniation at the time of chymopapain injection. The wink sign is an additional objective finding that can be used in assessing the patient with sciatica.

Adult↗
PubMed1986

Individual variation in botulism.

Mice were treated per os with one oral LD100 of toxic filtrate from a culture of Clostridium botulinum type C. The period between dosing and the first appearance of clinical signs varied greatly (2-31 h) from one animal to another. The duration of the pre-clinical and clinical phases together ranged from 5.5 to greater than 55 h. The duration of the clinical phase alone ranged from 1.25 to greater than 24 h, except for a minority of mice in which death occurred suddenly from apparent heart failure with no premonitory signs 4.75-31 h after dosing. Toxaemia was demonstrable in all mice that had just begun to show a clinical response 3.75-6.5 h after dosing, and in some that had not. Outside these time limits toxaemia was demonstrable only rarely, and beyond 12 h after dosing never. Therefore the many (approximately 50%) mice that began to show clinical signs more than 12 h after dosing had no demonstrable toxaemia throughout the entire clinical phase of the disease. The concentrations of toxin demonstrated in the blood ranged from less than 5 to greater than or equal to 20 (but less than 40) intravenous mouse-lethal doses/ml.

Animals↗
PubMed1986

Serological response of mice to Fusobacterium necrophorum.

Mice immunised with killed or living Fusobacterium necrophorum, by five different regimens, almost invariably failed to produce antibodies demonstrable by a passive haemagglutination test. An enzyme-linked immunosorbent assay (ELISA), however, usually demonstrated a serum antibody response. This suggested that F necrophorum was not in fact immunosuppressive in mice--a possibility that had been entertained to explain the great difficulty in protecting mice immunologically against challenge with F necrophorum.

Animals↗
PubMed1986

Patients with multiple unexplained symptoms. Their characteristics, functional health, and health care utilization.

To define groups of patients with inappropriately high health care utilization better, we have studied a group of 41 chronically ill patients to determine their characteristics, symptoms, functional health status, and amount of health care utilization. This group had somatization disorder diagnosed by specific criteria. They can be easily recognized by primary care physicians by their multiple complaints, negative physical examination results, and a history of multiple medical examinations. We found them to be functionally disabled, spending an average of seven days ill in bed each month. They perceived themselves as severely ill and were willing to undergo multiple hospitalizations, diagnostic studies, and operations. Their health care charges were extraordinary, averaging $4,700 annually. The physician can most effectively treat these patients by scheduling regular visits, relying on physical examinations rather than diagnostic studies, and avoiding costly hospitalizations.

Adult↗
PubMed1985

Substrate specificity of the DNA unwinding activity of the RecBC enzyme of Escherichia coli.

The RecBC enzyme of Escherichia coli promotes genetic recombination of phage or bacterial chromosomes. The purified enzyme travels through duplex DNA, unwinding and rewinding the DNA with the transient production of potentially recombinogenic single-stranded DNA. The studies reported here are aimed at understanding which chromosomal forms allow the entry of RecBC enzyme and hence may undergo RecBC enzyme-mediated recombination. Circular duplex molecules, whether covalently closed, nicked or containing single-stranded gaps of 10 to 774 nucleotides, are not detectably unwound by RecBC enzyme. Linear duplex molecules are readily unwound if they have a nearly flush-ended terminus whose 5' and 3' ends are offset by no more than about 25 nucleotides; molecules with longer single-stranded tails are poorly bound by RecBC enzyme and are infrequently unwound. The single-strand endonuclease activity of RecBC enzyme can slowly cleave gapped circles to produce molecules presumably capable of being unwound. These results provide an enzymatic basis for the recombinogenicity of double-stranded DNA ends established from genetic studies of RecBC enzyme and Chi sites, recognition sites for RecBC enzyme-mediated DNA strand cleavage.

Autoradiography↗
PubMed1985

Role of Escherichia coli RecBC enzyme in SOS induction.

Induction of the SOS genes is required for efficient repair of damaged DNA in Escherichia coli. SOS induction by nalidixic acid or oxolinic acid, two inhibitors of DNA gyrase, requires the RecBC enzyme of E. coli. We report here that the nuclease activity of RecBC enzyme is not needed for SOS induction by these agents. We suggest that the unwinding activity of RecBC enzyme produces single-stranded DNA which activates the RecA protein to stimulate LexA repressor cleavage and SOS induction.

DNA Repair↗
PubMed1985

Chi-dependent DNA strand cleavage by RecBC enzyme.

Chi sites enhance in their vicinity homologous recombination by the E. coli RecBC pathway. We report here that RecBC enzyme catalyzes Chi-dependent cleavage of one DNA strand, that containing the Chi sequence 5'G-C-T-G-G-T-G-G3'. Chi-specific cleavage is greatly reduced by single base pair changes within the Chi sequence and by mutations within the E. coli recC gene, coding for a RecBC enzyme subunit. Although cleavage occurs preferentially with double-stranded DNA, the product of the reaction is single-stranded DNA. These results demonstrate the direct interaction of RecBC enzyme with Chi sites that was inferred from the genetic properties of Chi and recBC, and they support models of recombination in which Chi acts before the initiation of strand exchange.

Base Sequence↗
PubMed1985

RecBC enzyme nicking at Chi sites during DNA unwinding: location and orientation-dependence of the cutting.

Homologous recombination by the E. coli RecBC pathway occurs at elevated frequency near Chi sites. We reported previously that Chi induces RecBC enzyme to cleave one DNA strand--that containing the Chi sequence 5'G-C-T-G-G-T-G-G3'. We report here that the Chi-dependent cleavage occurs four, five, or six nucleotides to the 3' side of the Chi octamer and produces nicks with 3'-OH and 5'-PO4 groups. Chi-dependent cleavage occurs if RecBC enzyme approaches the Chi sequence from the right, but not if it approaches only from the left, during unwinding of the duplex DNA substrate. A single RecBC enzyme molecule appears to cleave the DNA and to release part of it as a single-stranded fragment. These and previous results indicate that Chi-dependent cleavage is concomitant with DNA unwinding by RecBC enzyme and provide an enzymatic basis for the orientation-dependence of Chi recombinational hotspot activity. These observations demonstrate a key step of a proposed model of recombination in which RecBC enzyme produces a potentially invasive single-stranded DNA tail extending from Chi to its left. We discuss the relation between the action of Chi sites and that of special sites enhancing eukaryotic recombination.

Base Sequence↗
PubMed1985

Somatization disorder in men.

Somatization disorder is thought to be rare in men. This paper reviews five previously reported cases of somatization disorder in men and reports nine new cases referred from primary care physicians. These men have most of the associated features of the disorder, are of lower socioeconomic status, and have other significant psychiatric diagnoses. Eight of the nine men had a dramatic precipitating event at the onset of their illness. This diagnosis appears to be applicable to men and needs to be considered in men with multiple, recurrent unexplained medical symptoms.

Adult↗
PubMed1985

The weak immunogenicity of Fusobacterium necrophorum.

Three of four extreme methods of immunization completely failed to protect mice against challenge with the homologous strain of Fusobacterium necrophorum. Unsuccessful vaccines included (1) broth culture killed by mild heat and emulsified with Freund's complete adjuvant, and (2) a homogenate of heavily infected mouse brains, inactivated by mild heat and given in two doses. Also unsuccessful as a method of immunization was the production of a severe subcutaneous infection with F. necrophorum, followed by curative treatment with metronidazole. Slight but significant protection against subcutaneous challenge resulted, however, from two such infections given in rapid succession. It would appear that the main virulence factors of F. necrophorum are only weakly immunogenic, and the experiments give little encouragement to the prospect of an effective necrobacillosis vaccine.

Animals↗
PubMed1985

Demonstration of cross-reactive antigens in F38 and related mycoplasmas by enzyme-linked immunosorbent assay (ELISA) and immunoblotting.

The ELISA and an immunoblotting technique were used to study F38-type mycoplasmas - an important cause of contagious caprine pleuropneumonia - and a number of related mycoplasma species, subspecies, types or serogroups. Two-way ELISA cross-reactivity was demonstrated between five mycoplasmas, namely strain F38, Mycoplasma mycoides subsp. mycoides (LC strain), M. equigenitalium, M. primatum and bovine serogroup 7. In addition one-way cross-reactivity was demonstrated between F38 and each of the following mycoplasmas: M. mycoides subsp. mycoides (two SC strains), M. mycoides subsp. capri, and bovine serogroup L. F38 and M. capricolum did not cross-react. Immunoblot analysis, unlike ELISA, revealed that F38 and M. capricolum were closely related. At least four major protein antigens were shared between F38, M. mycoides subsp. mycoides (SC and LC strains), M. mycoides subsp. capri and bovine serogroup 7. The ELISA cross-reactions (above) shown by M. equigenitalium and M. primatum with each other, with F38 and with other mycoplasmas were not apparent by immunoblotting.

Antigens, Bacterial↗
PubMed1985

Family histories of depressed and severely anxious children.

Of 127 relatives of 12 anxious and 11 depressed children, 72% received Family History RDC diagnoses, most commonly depression and alcoholism. The family histories of the two groups were similar, suggesting that childhood depressive and anxiety disorders may be familially related.

Age Factors↗
PubMed1985

Psychologic modulation of the human immune response to varicella zoster.

Psychoimmunology, the interrelationship between the brain/mind/psyche and the immune system, is now an established area of scientific research. Based on prior investigations we hypothesized that an experienced meditator could affect her delayed hypersensitivity reaction by a psychological process. A single-case study design was employed in which the subject was skin tested weekly with varicella zoster skin test reagent. After baseline immunologic studies, she was able, as hypothesized, to significantly reduce both the induration of her delayed hypersensitivity skin test reaction and in vitro lymphocyte stimulation to varicella zoster. Then, as predicted, she was able to allow her reaction to return to baseline. As a confirmation of what is to our knowledge this previously undescribed phenomenon, she was able to reproduce the entire sequence nine months later. It appears that this subject can intentionally modulate her immune response by a psychologic mechanism.

Antigens, Viral↗