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1.
Pneumocystis carinii is the prime opportunistic pathogen of our time, the leading cause of fatal pneumonia in the increasing number of immunosuppressed subjects encountered on oncology and transplant programmes' and in subjects with the acquired immuno-deficiency syndrome (AIDS). 相似文献
2.
Ann E. Wakefield Sarah E. Peters Suneale Banerji Paul D. Bridge Geoffrey S. Hall David L. Hawksworth Lynden A. Guiver rew G. Allen Julian M. Hopkin 《Molecular microbiology》1992,6(14):1903-1911
Pneumocystis carinii causes life-threatening pneumonia in T-lymphocyte-immunodeficient subjects in transplant and oncology units or with acquired immune deficiency syndrome (AIDS). Recent DNA homology studies show P. carinii to be a fungus. To investigate the biology and epidemiology of this parasite further, we elected to determine for it a more precise taxonomic assignment within the fungal kingdom. We screened a wide range of organisms representing the major orders of fungi using DNA amplification and subsequently sequenced a portion of the mitochondrial gene encoding the large subunit ribosomal RNA. Our data show that the opportunistic pulmonary pathogen P. carinii is closely related to the ustomycetous red yeast fungi, a group which includes organisms that are extensively distributed throughout the environment and which release many widely dispersed airborne spores. 相似文献
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In deciduous woodlands near to Bristol, South-west England, about one in ten specimens of the woodlouse Oniscus asellus (L.) are infested with Bakerdania elliptica (Krczal, 1959), a small pygmephorid mite of about 200 pm in length. Woodlice in the field rarely carry more than three mites, which are usually attached to the mid or lateral regions of the sixth and seventh pereonites on the ventral surface of the isopod. These 'favoured sites' correspond to regions of the exoskeleton of the woodlouse which are free from abrasion as they move through leaf litter. Mites removed from these areas and replaced on the first pereonite return to a favoured site, usually within 30 min. During this process they exhibit four distinct types of behaviour.]
Uninfested specimens of Oniscus usellus maintained in laboratory tanks on leaf litter from their 'own' site all become infested with mites within a week. The number of mites on the isopods increases rapidly under these conditions. After six weeks, each individual carries a mean of about 50 mites. The level of infestation is subsequently stable, probably due to saturation of favoured sites, since large numbers of unattached mites can be found in the leaf litter during this period.
Studies by light microscopy and scanning electron microscopy have shown that Bakerdania elliptica does not feed while attached to the cuticle of Oniscus asellus , and that all attached mites are females. Males are extremely rare and occur only in leaf litter. These observations suggest that the relationship between Bakerdania elliptica and Oniscus asellus is one of phoresy and that female mites use woodlice as an aid to dispersal during their life cycle. 相似文献
Uninfested specimens of Oniscus usellus maintained in laboratory tanks on leaf litter from their 'own' site all become infested with mites within a week. The number of mites on the isopods increases rapidly under these conditions. After six weeks, each individual carries a mean of about 50 mites. The level of infestation is subsequently stable, probably due to saturation of favoured sites, since large numbers of unattached mites can be found in the leaf litter during this period.
Studies by light microscopy and scanning electron microscopy have shown that Bakerdania elliptica does not feed while attached to the cuticle of Oniscus asellus , and that all attached mites are females. Males are extremely rare and occur only in leaf litter. These observations suggest that the relationship between Bakerdania elliptica and Oniscus asellus is one of phoresy and that female mites use woodlice as an aid to dispersal during their life cycle. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
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The efficacy of facemask resuscitation was assessed by measuring the expiratory tidal volume during the first three inflations in nine babies with birth asphyxia and comparing the results with those obtained in a further nine babies resuscitated after endotracheal intubation. The facemask system was relatively inefficient, with tidal exchange less than one third of that seen after intubation and rarely sufficient to produce adequate alveolar ventilation. Successful resuscitation depended on stimulating the baby to make his own respiratory efforts. 相似文献
10.
The cytotoxic effect of cigarette smoke condensate on human polymorphs was investigated in vitro by the method of vital dye exclusion. Exposure to 1/800 of the smoke from one high-tar cigarette killed a detectable proportion of a population of 10(6) cells. The response among the cells from 40 healthy people varied widely, the percentage of dead cells ranging from 3% to 66% and from 17% to 87% at exposure levels of 125 micrograms and 250 micrograms cigarette smoke condensate respectively. Differences in individuals'' responses were reproducible and unrelated to age or sex or smoking habit. The cells from 10 patients with irreversible obstructive airways disease and probable emphysema were significantly more sensitive than those from 10 patients with no respiratory disability matched for age and smoking habits. Genetically influenced variation in cellular response to cytotoxicity may be an important determinant of the risk of developing emphysema among smokers. 相似文献