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Biomedical subjects

M Duncan

Publications and source records attributed to M Duncan.

At least 19 recordsLinked to original sources
PubMed2001

A profile of neurology practice based on Medicare services: an AAN Medical Economics and Management Committee report. American Academy of Neurology.

OBJECTIVE: This report uses Medicare data to provide insight into the patient care services most often provided by neurologists. METHODS: The 1998 Medicare data set for physician services was obtained from the Health Care Financing Administration. Neurologists' services were tabulated and compared to the 1998 American Academy of Neurology Member Demographic and Practice Characteristics Report. A profile was derived of neurologists' typical services. RESULTS: Patient visits represent 70% of neurologists' services when evaluated by income. Office was the site of service for 62% of patient visit income. Established patients were 29% of patient visit income. Neurologists frequently code patient visits at levels of service higher than used by other physicians. EMG and nerve conduction velocity together represent 55% of neurodiagnostic services when evaluated by income. CONCLUSIONS: Patient care continues to be the main service of neurologists, with office care more than hospital care. Established patient care is an important part of patient services, confirming the role of the neurologist in principal care. Neurologists' patient care levels of service are higher than for other physicians.

Medicare↗
PubMed2001

Genotypic diversity of mutans streptococci in Brazilian nursery children suggests horizontal transmission.

Streptococcus mutans strains were isolated from cohorts of Brazilian nursery school children and genotyped by arbitrarily primed PCR and restriction fragment length polymorphism analysis. Of 24 children with two to five S. mutans isolates, 29% carried two or more genotypes. The presence of matching genotypes of S. mutans among children attending one nursery suggests horizontal transmission.

Brazil↗
PubMed1998

Comparative analysis of Haemophilus influenzae hifA (pilin) genes.

Adherence of Haemophilus influenzae to epithelial cells plays a central role in colonization and is the first step in infection with this organism. Pili, which are large polymorphic surface proteins, have been shown to mediate the binding of H. influenzae to cells of the human respiratory tract. Earlier experiments have demonstrated that the major epitopes of H. influenzae pili are highly conformational and immunologically heterogenous; their subunit pilins are, however, immunologically homogenous. To define the extent of structural variation in pilins, which polymerize to form pili, the pilin genes (hifA) of 26 type a to f and 16 nontypeable strains of H. influenzae were amplified by PCR and subjected to restriction fragment length polymorphism (RFLP) analysis with AluI and RsaI. Six different RFLP patterns were identified. Four further RFLP patterns were identified from published hifA sequences from five nontypeable H. influenzae strains. Two patterns contained only nontypeable isolates; one of these contained H. influenzae biotype aegyptius strains F3031 and F3037. Another pattern contained predominantly H. influenzae type f strains. All other patterns were displayed by a variety of capsular and noncapsular types. Sequence analysis of selected hifA genes confirmed the 10 RFLP patterns and showed strong identity among representatives displaying the same RFLP patterns. In addition, the immunologic reactivity of pili with antipilus antisera correlated with the groupings of strains based on hifA RFLP patterns. Those strains that show greater reactivity with antiserum directed against H. influenzae type b strain M43 pili tend to fall into one RFLP pattern (pattern 3); while those strains that show equal or greater reactivity with antiserum directed against H. influenzae type b strain Eagan pili tend to fall in a different RFLP pattern (pattern 1). Sequence analysis of representative HifA pilins from typeable and nontypeable H. influenzae identified several highly conserved regions that play a role in bacterial pilus assembly and other regions with considerable amino acid heterogeneity. These regions of HifA amino acid sequence heterogeneity may explain the immunologic diversity seen in intact pili.

Amino Acid Sequence↗
PubMed1998

Role of Arg-gingipain A in virulence of Porphyromonas gingivalis.

In order to access the role of the Porphyromonas gingivalis Arg-gingipain proteases in the virulence of this organism, a mutant defective in the rgpA gene was constructed in strain 381. This mutant, MT10, displayed only 40% of the Arg-specific cysteine protease activity of the wild-type strain. In addition, MT10, as well as the recently characterized protease mutant G-102, which is defective in the rgpB gene, displayed reduced self-aggregation, hemagglutination, and the ability to bind to immobilized type I collagen compared to levels of the wild-type parent. However, unlike mutant G-102, the rgpA mutant displayed increased binding to epithelial cells relative to that of the parental organism. Mutant MT10 also did not express detectable levels of the FimA protein as assessed by both Western and Northern blotting or fimbriae visible by electron microscopy of the cells. Furthermore, the ability of MT10 to degrade rat tail collagen fibers when it was cultured at 37 degrees C was markedly attenuated compared to that of strain 381. These results suggest that Arg-gingipain A may play a significant role in the pathogenicity of P. gingivalis by altering the colonization and toxic properties of the organism.

Adhesins, Bacterial↗
PubMed1998

How is whole body protein turnover perturbed in growth hormone-deficient adults?

Adult patients with GH deficiency have reduced lean body mass (LBM), muscle mass, and muscle strength, suggesting an underlying abnormality of protein metabolism. As acute GH administration has previously been reported to decrease protein oxidation and increase protein synthesis in GH-deficient (GHD) adults, we investigated whether the converse might occur in untreated GH deficiency by undertaking studies of whole body protein turnover in 10 GHD and 13 normal subjects using a 3-h primed constant infusion of 1-[13C]leucine. Dual energy x-ray absorptiometry was used to quantify LBM and fat mass (FM). In normal subjects, LBM was the major, independent determinant of leucine appearance (Ra; r=0.80; P=0.0009), leucine oxidation (r=0.81; P=0.0008), and leucine incorporation into protein (r=0.75; P= 0.003). However, in an analysis of covariance, FM was also a significant independent determinant of leucine Ra (P=0.002) and leucine incorporation into protein (P=0.003). After correcting for LBM and FM, GHD patients had significantly reduced rates of leucine Ra (109.9+/-4.4 vs. 125.5+/-3.7 micromol/min, respectively; P=0.02) and leucine incorporation into protein (87.0+/-3.9 vs. 100.3+/-3.3 mmol/ min; P=0.02) compared to normal subjects. There was no significant difference in the corrected rates of leucine oxidation between the two groups (22.9+/-1.3 vs. 25.2+/-1.0, GHD vs. normal; P=0.20). In summary, GHD adults have reduced rates of protein synthesis and protein breakdown, but normal rates of irreversible oxidative loss; these findings are discordant with what was predicted from the acute changes in protein metabolism observed with GH administration. We conclude that normalization of protein oxidation may be a homeostatic mechanism that operates to constrain protein loss in GHD adults.

Adipose Tissue↗
PubMed1997

The nucleotide sequence of Saccharomyces cerevisiae chromosome V.

Here we report the sequence of 569,202 base pairs of Saccharomyces cerevisiae chromosome V. Analysis of the sequence revealed a centromere, two telomeres and 271 open reading frames (ORFs) plus 13 tRNAs and four small nuclear RNAs. There are two Tyl transposable elements, each of which contains an ORF (included in the count of 271). Of the ORFs, 78 (29%) are new, 81 (30%) have potential homologues in the public databases, and 112 (41%) are previously characterized yeast genes.

Base Sequence↗
PubMed1997

Multiple colonization defects in a cysteine protease mutant of Porphyromonas gingivalis.

A cysteine protease mutant, G-102, of Porphyromonas gingivalis 381 defective in the rgp-1 gene has been recently constructed in this laboratory. In order to evaluate the role of the protease in the virulence properties of P. gingivalis, a number of putative periodontopathic properties of the mutant were evaluated. Relative to the parental strain, mutant G-102 was demonstrated to be defective in interacting with Gram-positive bacteria as well as cultured epithelial cells. In addition, the mutant was altered in attaching to the protein components of extracellular matrix as well as to type I collagen. Some of these alterations could result from the decreased autoaggregation displayed by mutant G-102 relative to strain 381. However, since the epithelial cell attachment assays were carried out at very low bacterial densities, it is unlikely that reduced autoaggregation of the mutant is responsible for its decreased ability to attach to these eucaryotic cells. Electron microscopic examination of the cells also revealed that mutant G-102 was altered in normal fimbrae expression. In addition, reduced expression of the 43 kDa fimbrial subunit in the mutant was detected with both Western and Northern blotting. These results indicated that the rgp-1 gene product can play either a direct or indirect role in the colonization properties of P. gingivalis.

Adhesins, Bacterial↗
PubMed1996

Unusual complications of cervical spine surgery for cervical myelopathy in rheumatoid arthritis.

Cervical myelopathy is a recognized complication of rheumatoid arthritis and other inflammatory arthropathies. In a significant proportion of patients, surgical stabilization of the cervical spine offers the best opportunity for improvement of symptoms and long-term survival. We report two cases that illustrate some potential complications of cervical spine surgery and which also emphasize the need for vigilance when caring for patients in this group.

Arthritis, Rheumatoid↗
PubMed1996

Role of Porphyromonas gingivalis protease activity in colonization of oral surfaces.

Cysteine proteases, including Arg-gingipain of Porphyromonas gingivalis, have been implicated as important virulence factors in periodontal diseases. These enzymes are also involved in the hemagglutinating activity of the organisms. In order to determine the role of proteases in the colonization of the gingival margin, we have compared the attachment properties of P. gingivalis 381 with those of its Arg-gingipain-defective mutant, G-102. Interactions with gram-positive bacteria, human oral epithelial cells, extracellular matrix proteins, and type I collagen were evaluated. In all cases, mutant G-102 was deficient in attachment relative to the parental strain. The mutant's defects could be explained, in part, by the weak autoaggregation displayed by the mutant, which appeared to result from altered fimbrial expression. Both Western blot (immunoblot) and Northern (RNA) blot analyses indicated reduced expression of the major 43-kDa fimbrillin subunit in the mutant. These results suggest that Arg-gingipain may play both direct and indirect roles in the colonization of the gingival margin. In addition, fimbriae may play a direct role in interacting with some host surfaces.

Bacterial Adhesion↗
PubMed1995

Cross-species identification of proteins separated by two-dimensional gel electrophoresis using matrix-assisted laser desorption ionisation/time-of-flight mass spectrometry and amino acid composition.

Amino acid analysis and matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry were used to identify nine of twelve proteins originally separated by two-dimensional electrophoresis and derived from an organism poorly defined at the molecular level (Spiroplasma melliferum). Two of three unidentified proteins appeared to be novel. The percentage amino acid composition and the molecular mass of peptide fragments generated by tryptic digestion were used to search the PIR/SWISS-PROT and MOWSE databases respectively. Lists of candidate proteins were independently generated and ranked from data obtained by both methods. A putative identification was allocated when a single candidate protein appeared in both lists of computer-generated rankings. Results were verified using N-terminal protein microsequencing. The combined use of amino acid composition and MALDI-TOF mass spectrometry allowed a high degree of confidence to be placed in such identifications because they were based upon homologous data sets of at least 20 parameters (16 amino acids and 4-10 tryptic digest fragments). A further two parameters, estimated M(r) and, to a lesser extent, pI, were also used to reinforce this measure of confidence. Ranking of candidate proteins by one method alone could lead to false identification. Both techniques can process large numbers of samples rapidly. In light of the increasing number of entries in both gene and protein databases, this approach is likely to become an essential first step for the characterisation of proteins, particularly across species boundaries.

Amino Acid Sequence↗
PubMed1995

Hypopi (Acari: Hypoderatidae) from subcutaneous tissues of the African spoonbill (Aves: Ciconiiformes: Threskiornithidae).

Two new species and a new host record for two additional species of deutonymphs of the family Hypoderatidae are described from subcutaneous adipose tissues of a captive African spoonbill, Platalea alba Scopali. Phalacrodectes (Phalacrodectes) platalea Pence & Duncan, n. sp. most closely resembles P. (P.) whartoni Fain and P. (P.) pelecani Pence & Courtney in chaetotaxy and cuticular sclerotization, but it differs by having secondary perigenital sclerotization surrounding the genital openings and parallel genital papillae. P. (P.) schoutedeni Fain is reexamined for the first time since its original description, which was based on a single specimen from a cormorant; we believe the affinity of this species is closer to those infecting ibises and spoonbills and that the former record was a case of accidental host capture among birds sharing the same rookery. A new host record is established for Neottialges platalea Fain & Laurence from the African spoonbill. The heavy idiosomal sclerotization, incomplete genital apodeme, and long dorsal setae differentiate Neottialges intermedius Pence & Duncan, n. sp. from all other species in the genus. Because this suite of characters was previously used to separate the three subgenera of the genus Neottialges, we propose that Neottialges, Caloenectes, and Pelecanectes should now be considered invalid subgeneric taxa.

Animals↗
PubMed1994

Evidence that L-(+)-lactate dehydrogenase deficiency is lethal in Streptococcus mutans.

In order to construct an effector strain for the replacement therapy of dental caries, we wished to combine the properties of low-level acid production and high-level colonization potential in a strain of Streptococcus mutans. To this end, we made a deletion in the lactate dehydrogenase (LDH) gene cloned from the bacteriocin-producing S. mutans strain JH1000. However, we were unable to substitute the mutant for the wild-type allele by transformation with linear DNA fragments. The mutated gene, carried on a suicide vector, was shown by Southern analysis to integrate into the JH1000 chromosome to yield transformants carrying both the wild-type gene and mutated LDH gene. Three spontaneous self-recombinants of one heterodiploid strain were isolated by screening 1,500 colonies for a loss of the tetracycline resistance encoded by the gene used to mark the LDH deletion. In all three cases, Southern analysis showed that a loss of tetracycline resistance was accompanied by a loss of the mutated LDH gene, resulting in restoration of the wild-type genotype. However, screening the same number of colonies for self-recombinants that did not make lactic acid during anaerobic growth in Todd-Hewitt broth failed to identify clones in which the wild-type allele was lost. A second, simpler screening of more than 80,000 colonies grown aerobically on glucose tetrazolium medium to identify low-level-acid-producing colonies was also unsuccessful. These results are interpreted as indicating that LDH deficiency is lethal in S. mutans under the cultivation conditions used in these experiments. The physiological bases for this hypothesis are described.

Blotting, Southern↗