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Biomedical subjects

D M Collins

Publications and source records attributed to D M Collins.

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

Women's advancement in medicine and academia: barriers and future perspectives.

Although women made early advancements in the field of medicine during the second half of the 19th century, they were not able to make relevant strides in both medicine and academia until the 1960s. Despite women's recent advancements, obstacles and barriers to their hope of achieving fairness and equality in their professional and academic careers still exist. These practices include professional discrimination, blatant sexism, lack of appropriate mentors, and unfair faculty promotion processes. In this article, we address the most common problems affecting women physicians' advancement in academic medicine. We also focus on the role of mentorship as a relevant and beneficial factor for progress in their medical and academic careers. Finally, we provide a perspective designed to resolve most of the barriers confronting women physicians in their quest for advancement in academic medicine.

Career Mobility↗
PubMed1996

Electroporation at elevated temperatures substantially improves transformation efficiency of slow-growing mycobacteria.

The effects of electroporation temperature, biochemical pretreatment of cells and stage of culture on electroporation efficiency for slow-growing mycobacteria were investigated. The efficiency of transformation into Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium intracellulare increased markedly with temperature. In contrast, the efficiency of transformation into Mycobacterium smegmatis, a fast-growing species, was higher at 0 degree C and decreased with temperature. While stage of culture had little effect, a further increase in efficiency of 2-4-fold was obtained following glycine or ethionamide pretreatment. Electroporation at 37 degrees C has been chosen as a standard condition for slow-growing species as it usually resulted in a transformation efficiency several orders of magnitude higher than that obtained at 0 degree C.

Bacteriological Techniques↗
PubMed1996

In search of tuberculosis virulence genes.

The identity of the virulence genes that enable tuberculosis organisms to survive in macrophages and to induce the features of tuberculosis remains largely unknown. Numerous putative virulence genes have been identified, but so far there is only conclusive evidence for the role of two genes, KatG and rpoV, in virulence.

Bacterial Proteins↗
PubMed1996

ahpC, a gene involved in isoniazid resistance of the Mycobacterium tuberculosis complex.

A gene conferring low-level isoniazid (INH) resistance on Mycobacterium smegmatis was isolated from a cosmid library of the genome of an INH-resistant Mycobacterium bovis strain. The gene had good homology with ahpC, the product of which is a subunit of alkyl hydroperoxide reductase, and also with a family of thiol-specific antioxidant enzymes. A mutation was found in the promoter upon comparison with the equivalent DNA sequence from the INH-sensitive parent strain. Promoter sequences from other INH-sensitive and INH-resistant M. bovis and Mycobacterium tuberculosis strains were sequenced and the mutation was found only in the INH-resistant strains. An INH-resistant M. tuberculosis strain also had an additional mutation in the promoter region. The wild-type promoter and promoters with one and two mutations were ligated into a reporter plasmid containing the lacZ gene. The presence of the first mutation resulted in a sixfold induction of beta-galactosidase activity, and the presence of both mutations caused a 10-fold induction. Increased expression of AhpC may account for some of the INH resistance of strains of the M. tuberculosis complex.

Amino Acid Sequence↗
PubMed1995

Mutation of the principal sigma factor causes loss of virulence in a strain of the Mycobacterium tuberculosis complex.

Tuberculosis continues to be responsible for the deaths of millions of people, yet the virulence factors of the causative pathogens remain unknown. Genetic complementation experiments with strains of the Mycobacterium tuberculosis complex have identified a gene from a virulent strain that restores virulence to an attenuated strain. The gene, designated rpoV, has a high degree of homology with principal transcription or sigma factors from other bacteria, particularly Mycobacterium smegmatis and Streptomyces griseus. The homologous rpoV gene of the attenuated strain has a point mutation causing an arginine-->histidine change in a domain known to interact with promoters. To our knowledge, association of loss of bacterial virulence with a mutation in the principal sigma factor has not been previously reported. The results indicate either that tuberculosis organisms have an alternative principal sigma factor that promotes virulence genes or, more probably, that this particular mutant principal sigma factor is unable to promote expression of one or more genes required for virulence. Study of genes and proteins differentially regulated by the mutant transcription factor should facilitate identification of further virulence factors.

Amino Acid Sequence↗
PubMed1995

Bovine tuberculosis in Swedish deer farms: epidemiological investigations and tracing using restriction fragment analysis.

Bovine tuberculosis was eradicated from Sweden after a programme lasting many years. By 1991, no tuberculosis in wildlife had been discovered for 50 years and the last case in cattle had occurred 13 years before. In 1991, the disease was identified in a herd of farmed fallow deer (Dama dama) and over the next three years nine other infected herds were identified. Investigation revealed that all the infected deer were either deer that had been imported into Sweden from the United Kingdom in 1987 or had been in contact with them. Restriction fragment analysis of eight isolates of Mycobacterium bovis from five of the herds showed that the isolates had identical patterns of DNA fragments, which indicated a common source of infection. Among more than 800 isolates of M bovis that have been analysed, these patterns were identical to those of only two previous isolates, both of which came from British deer. These results indicate that the eight Swedish strains of M bovis and the two British strains may have a common source of infection.

Animals↗
PubMed1995

Detection of Mycobacterium bovis in tissues by polymerase chain reaction.

A polymerase chain reaction (PCR) test was developed to detect Mycobacterium bovis in tissues. The test was based on amplification of a 248 bp segment of the insertion sequence, IS1081, present in six copies in strains of M. bovis and other members of the tuberculosis complex. The procedure involved digestion with proteinase K, lysis with sodium dodecyl sulphate, and extraction with hexadecyl tetramethyl ammonium bromide and phenol:chloroform:iso-amyl alcohol. When agarose gel electrophoresis was used for detection, the method was able to detect 1 fg of pure DNA, or 0.2 genome equivalents. It could also detect as few as 10 organisms from pure cultures and between 200-500 organisms from tissues spiked with cultured organisms. Detection by hybridization was only marginally more sensitive. The method was tested on 110 selected tissues recovered post mortem from a variety of animals. Fifty three of 58 samples diagnosed as M. bovis culture positive, including all samples containing microscopically visible acid-fast bacilli, were positive on duplicate testing by PCR. Five of 52 culture negative samples were also positive by PCR including three which contained large numbers of acid-fast organisms. Ten of the culture negative samples came from animals in a herd known to be free of bovine tuberculosis and all these were negative by PCR.

Animals↗
PubMed1995

A study of bovine tuberculosis in domestic animals and wildlife in the MacKenzie Basin and surrounding areas using DNA fingerprinting.

The MacKenzie Basin, an area of about 5150 km2 in the South Island of New Zealand, was free of bovine tuberculosis prior to 1980. During the next 13 years, the majority of the cattle and deer herds in this area became infected with Mycobacterium bovis. The history of infection in the MacKenzie Basin has all the characteristics of a newly developed region of endemic tuberculosis with a wildlife reservoir of M. bovis. Tuberculous possums and ferrets were found in the MacKenzie Basin and both may have been a source of infection for domestic animals. DNA fingerprinting of 125 isolates of M. bovis from domestic animals and wildlife by restriction endonuclease analysis revealed two major groups of isolates. The same groups were identified using IS6110 as a DNA probe. Restriction endonuclease analysis enabled one group to be subdivided into seven restriction types and the other group into eight types. Mycobacterium bovis isolates with the most common restriction types were present in both domestic animals and wildlife, indicating that infection had spread between these two groups of animals. DNA fingerprinting also revealed that M. bovis was introduced into the MacKenzie Basin from at least two distinct sources. Furthermore, DNA finger-printing was able to identify probable sources of infection.

Journal Article↗
PubMed1995

Identification of bovine T cell stimulatory antigens using a cosmid library of Mycobacterium bovis in Mycobacterium smegmatis.

Culture filtrates derived from a Mycobacterium bovis cosmid library in Mycobacterium smegmatis were screened for T cell antigens. Recognition and reactivity were measured by the levels of lymphocyte proliferation and the levels of gamma interferon (IFN-gamma) produced when the culture filtrates were incubated with peripheral blood mononuclear cells (PBMC) taken from cattle immunised with M. bovis BCG. The screening system was optimised to distinguish between M. bovis secreted antigens and normal M. smegmatis secreted proteins. From ten culture filtrates screened, two were identified that induced lymphocyte proliferation and IFN-gamma production. Analysis of the DNA inserts from the recombinant cosmids suggest that they may code for different proteins. The results demonstrate that screening recombinant M. smegmatis culture filtrates can be used to identify M. bovis T cell antigens that are recognised by immunised cattle. These antigens may be important for the development of vaccines with protective ability against bovine tuberculosis.

Journal Article↗
PubMed1995

Effect of inhA and katG on isoniazid resistance and virulence of Mycobacterium bovis.

Isoniazid (INH) resistance of the Mycobacterium tuberculosis Complex (MtbC) is associated with both loss of catalase activity and mutation of the inhA gene. However, the relative contributions of these changes to resistance and to the loss of virulence for guinea-pigs is unknown. In this study, a virulent strain of Mycobacterium bovis, a member of the MtbC, was exposed to increasing concentrations of INH. Two INH-resistant strains were produced which had lost catalase activity. Strain WAg405, which had a higher resistance to INH, also had a mutation in the inhA gene. This demonstrated that loss of catalase activity and mutation of inhA had a cumulative effect on INH resistance. When a functional katG gene was integrated into the genome of WAg405 the INH resistance was greatly reduced. This indicated that most of the resistance had been caused by loss of catalase activity. While the parent INH-sensitive strain was virulent for guinea-pigs, the INH-resistant strains were significantly less virulent. Integration of a functional katG gene into the most resistant strain restored full virulence. This clearly established that katG is a virulence factor for M. bovis and that mutation of the inhA gene has no effect on virulence.

Animals↗
PubMed1995

Valproate in status epilepticus.

In patients with intractable status epilepticus who have not responded to therapy with benzodiazepines, phenytoin, and barbiturates, valproate may be a reasonable option. Extemporaneously prepared valproate rectal suppositories or retention enemas have been given in dosages of 200-1200 mg q6h in addition to phenytoin, phenobarbital, or both in adults. The pediatric dose used was 15-20 mg/kg, in addition to phenytoin and/or phenobarbital.

Animals↗
PubMed1994

Diagnosis and epidemiology of bovine tuberculosis using molecular biological approaches.

Conventional methods for diagnosis and epidemiological studies of bovine tuberculosis and other mycobacterial diseases are far from ideal. In the last twelve years, molecular biology has provided new approaches which have enabled detailed studies to be made of the molecular characteristics of Mycobacterium bovis, the causative organism of bovine tuberculosis. These characteristics have been investigated for their potential use in diagnosis and epidemiological studies. Restriction fragment analysis of genomic DNA from isolates of M. bovis has provided a highly discriminatory typing system which has been used extensively for epidemiological studies. DNA elements in M. bovis have been investigated for their potential use in diagnostic assays based on the polymerase chain reaction. Individual antigens of M. bovis and their reactive epitopes have been identified and investigated for their usefulness in both serological and T cell assays of animal infection. Serological assays have proven disappointing and the full potential of T cell assays has yet to be determined. Currently, T cell assays based on recombinant antigens have not been as sensitive as those based on natural antigens.

Animals↗
PubMed1993

Programs for phasing by entropy maximization as implemented in Xtal3.2: a crystallographic software system.

Xtal3.2, a crystallographic software package, is an international development project involving about 40 researchers over a full spectrum of crystallographic interests. This development has been supported by many national and international agencies and commercial institutions since the first version in 1983. The 1992 release, Xtal3.2, contains software for 95 different calculations. These range from the processing of raw diffraction data to interactive molecular graphics, atomic charge estimation, electronic publication preparation, and the structure solution and refinement of small and large molecules. Tests of the Xtal programs for phase determination and phase refinement by the application of 'maximum entropy' are presented.

Journal Article↗
PubMed1993

Entropy on charge density: making the quantum mechanical connection.

Entropy maximization has proven effective in treating certain aspects of the phase problem of X-ray diffraction. Much of its development has been expressed in probabilistic language, although image enhancement has been somewhat more physical or geometric in description. Here phasing and entropy maximization are embedded in the quantum mechanical problem of reconstructing an electronic one-matrix under experimental constraints. Entropy on an N-representable one-particle density matrix is well defined. The entropy is the expected form, and it is a simple function of the one-matrix eigenvalues which all must be non-negative. Certain other properties are pertinent to phasing which is implicit in one-matrix reconstruction governed by entropy maximization. Throughout this work reference is made to informational entropy, not the entropy of thermodynamics.

Journal Article↗
PubMed1993

Comparison of polymerase chain reaction tests and faecal culture for detecting Mycobacterium paratuberculosis in bovine faeces.

A polymerase chain reaction (PCR) test for M. paratuberculosis was developed based on a 218 bp segment of a DNA insertion sequence, IS900, that is specific for this organism. The method involved two consecutive amplification reactions, with the second set of primers being nested inside the first set. The method reliably detected 50 organisms/g faeces. This PCR test was applied to 32 bovine faecal specimens containing high, moderate or low numbers of M. paratuberculosis organisms as determined by culture. The PCR test detected all specimens containing > or = 1600 colony forming units (cfu)/g faeces, six of ten specimens with 160-480 cfu/g faeces but only two of 13 specimens containing < or = 112 cfu/g faeces. The sensitivity of this test was better than that of a commercial PCR test which was carried out on the same faecal specimens.

Animals↗