Search PubMed⌕ Search

Biomedical subjects

D A Powell

Publications and source records attributed to D A Powell.

At least 163 records · Page 9Linked to original sources
PubMed1979

Acute pulmonary blastomycosis in children: clinical course and follow-up.

The clinical courses of 14 children with acute pulmonary blastomycosis were studied. All the patients had a remarkably similar illness limited to the lungs with fever, malaise, and respiratory symptoms (cough, sputum production, chest pain, and vomiting). Despite eventual recovery with treatment in all instances, 13 of the 14 children persisted in having abnormal roentgenograms. Three children have demonstrated persistent mild obstructive airway disease for two to 12 months after completion of therapy. These data suggest that the initial illness following childhood infections with Blastomyces dematitidis is usually an acute pulmonary disease without systemic dissemination. Evidence of residual lung abnormalities conflicts with the recent concept of this being a benign, self-limited illness. Our findings suggest the importance of long-term follow-up as well as a need for more complete understanding of the full clinical spectrum and prognosis of acute pulmonary blastomycosis.

Adolescent↗
PubMed1978

Mycobacterial lymphadenitis in childhood.

A total of 42 cases of childhood mycobacterial adenitis have been studied to define the optimal steps that lead to the correct diagnosis of this disease. Antigens from the atypical mycobacteria are not currently available, so the usefulness of tuberculin skin testing as a diagnostic tool was examined. Skin testing differentiates mycobacterial adenitis from infection caused by pyogenic bacteria. In addition, repetitive skin testing with tuberculin over a three- to six-month period is also useful in differentiating adenitis caused by atypical mycobacteria from that due to Mycobacterium tuberculosis. Children with atypical mycobacterial adenitis have a decreasing tuberculin response to repeated testing, while children with tuberculous adenitis have a stable response. Other factors that assist in the differentiation of adenitides include a history of recent exposure to tuberculosis and evidence of extralymphatic tuberculosis. Needle aspiration or partial excision in mycobacterial adenitis may lead to drainage and sinus tract information. A PPD skin test should be done prior to surgical manipulation of enlarged nodes. Children with reactive skin tests should undergo complete excision.

Adolescent↗
PubMed1977

Structural studies on the specific type-14 pneumococcal polysaccharide.

The structure of the Pneumococcus type-14 capsular polysaccharide has been reinvestigated by using methylation analysis, different specific degradations, and n.m.r. spectroscopy. It is concluded that the polysaccharide is composed of tetrasaccharide repeating-units having the structure: (formula: see text).

Oligosaccharides↗
PubMed1977

Scanning electron microscopy of guinea pig alveolar macrophages: in vitro phagocytosis of Mycoplasma pneumoniae.

The scanning electron microscopic appearance of guinea pig alveolar macrophages during in vitro antibody-mediated phagocytosis of Mycoplasma pneumoniae is described. This study utilizes the ability of M. pneumoniae to attach to and replicate on a glass cover slip surrounding a monolayer of macrophages without inducing phagocytosis despite multiple points of interaction between organisms and macrophage filopodia. The addition of specific anti-M. pneumoniae serum to this system evokes a sequence of macrophage surface morphologic changes accompanied by engulfment of the surrounding mycoplasmas. The sequence of changes occurring over the 90 minutes subsequent to the addition of antiserum were visualized well with the scanning electron microscope and included the early appearance of elongated, rigid filopodia, the internalization of M. pneumoniae by ruffled membrane extensions, and finally the appearance of highly spread cells surrounded by large areas of cover slip cleared of M. pneumoniae.

Animals↗
PubMed1976

Orienting and classical conditioning in the rabbit (Oryctolagus cuniculus): effects of septal area lesions.

Rabbits with either sham or septal lesions recieved differential classical conditioning training in which tones of different frequencies served as CSs and paraorbital shock served as the UCS. Eyeblink (EB), EMG, and heart rate (HR) CRs were concommitantly assessed. Free field activity was also studied in selected animals. Animals with septal lesions revealed an impaired EB discrimination which resulted from increased responding to the CS-. These animals showed HR CRs of greater magnitude than sham animals. The HR discrimination was, however, unimpaired by septal lesions. Differential EMG activity also occurred, but was unaffected by septal destruction. Septal lesions resulted in greater free-field activity associated with visual stimulation, but no differences were obtained between septal and sham animals in the dark. It is suggested that these results were due to an enhanced reactivity to environmental stimulation, possibly related to dysfunctions of the orienting reflex.

Animals↗
PubMed1976

Mycoplasma pneumoniae in hamster tracheal organ culture studied by scanning electron microscopy.

Hamster tracheal rings in organ culture were inoculated with a virulent strain of Mycoplasma pneumoniae and examined by scanning electron microscopy. A progressive increase in epithelial cell injury was detected from 48 to 96 h post-inoculation and was characterized by apparent loss of the apical portion of ciliated cells. M. pneumoniae attaching to the epithelial cell surfaces could be identified by comparison with the surface morphology of mycoplasmas grown on glass cover slips.

Animals↗
PubMed1976

Attachment of Mycoplasma pneumoniae to respiratory epithelium.

The attachment of radioisotope-labeled Mycoplasma pneumoniae to hamster tracheal rings in organ culture was examined by radioautography and liquid scintillation counting. Radioautographs of individual rings exposed for 8 h to (3H) thymidine-labeled virulent M. pneumoniae revealed a dense extracellular collection of emulsion grains along the luminal surface of epithelial cells. Similar exposure of rings to isotope-labeled avirulent M. pneumoniae resulted in no accumulation of emulsion grains. The numbers of attached virulent mycoplasmas, as measured by liquid scintillation counting of infected rings, were found to increase in a nearly linear fashion over an 8-h incubation period. Viability of the mycoplasmas and metabolic integrity of the tracheal rings were important for optimal attachment. Pretreatment of rings with neuraminidase or sodium periodate significantly impaired orgainism adherence. These data suggest a specificity of interation between virulent M. pneumoniae and tracheal epithelial cells that can be further examined through the use of isotopically labeled mycoplasmas.

Animals↗
PubMed1975

A membrane-associated lipomannan in micrococci.

Membranes of Micrococcus lysodeikticus, Micrococcus flavus and Micrococcus sodonensis contain acidic lipomannans. Lipoteichoic acids could not be detected in these organisms, and the suggestion that they are substituted for by the lipomannans is strengthened by the chemical and physical resemblances between the two polymers. The mannans contain glycerol, ester-linked fatty acids and mono-esterified succinic acid residues, giving them both hydrophobic and charged properties. The M. lysodeikticus mannan has a chain of about 60 hexose units with two branch points, and is joined at its reducing end to the 1-position of a glycerol moiety bearing two fatty acid residues. Succinic acid on the mannan enables it to bind Mg2+ efficiently, and the polymer is firmly associated with the cytoplasmic membrane, probably by intercalation of its fatty acids with those of the membrane lipids.

Borohydrides↗
PubMed1975

Opsonin-reversible resistance of Mycoplasma pneumoniae to in vitro phagocytosis by alveolar macrophages.

Several species of mycoplasmas are responsible for respiratory disease in animals and man. As yet, little is known about the interaction of these pathogens with alveolar macrophages, one of the primary components of pulmonary resistance to infections. The present study was undertaken to develop an in vitro model to examine this organism-cell interaction, using a human pathogen, mycoplasma pneumoniae, and normal guinea pig alveolar macrophages. During a 24-h incubation of M. pneumoniae with a monolayer of macrophages, mycoplasmas were found to attach directly to the surface of the cells without inducing significant phagocytosis. Ultrastructurally, the organisms appeared bound to the cell membrane by their characteristic attachment organelles. Only after the addition of specific anti-mycoplasma serum were cells able to engulf attached and surrounding organisms. These data suggest that the interaction of M. pneumoniae and alveolar macrophages is a potentially important aspect of disease pathogenesis, and immune factors which might alter this interaction merit further examination.

Animals↗