Biomedical subjects
Publications and source records attributed to P Simonet.
The development of competence allowing natural transformation of Ralstonia solanacearum was found to occur during exponential growth and not in response to any excreted factors. Linear DNAs were effectively integrated by recombination requiring a minimum of 50 bp of homologous DNA. Therefore, DNA from other genera and species were ineffective.
Transfer by mobilization of a pBR derivative recombinant plasmid lacking transfer functions (oriT+, tra-, mob-) from one E. coli K12 strain to another was investigated in seven sterile microcosms corresponding to different environments. These microcosms were chosen as representative of environments that genetically engineered microorganisms (GEMOs) encounter after accidental release, namely attached biomass in aquatic environments (biofilm), soil, seawater, freshwater, wastewater, mouse gut, and mussel gut, GEMOs survived in the same way as the host strains in all microcosms. Recombinant DNA mobilization occurred in the mouse gut, in sterile soil, and in biofilm. The plasmid transfer rates principally reflected the environmental conditions encountered in each microcosm.
Just over sixty years ago, Yves Le Grand's article 'Sur la mesure de l'acuité visuelle au moyen de franges d'interférence' (C. R. Acad. Sci. Paris 200: 490-491; 1935) was published. A translation of this important article into English is given and a commentary discusses the application of the interference fringe method to the study of the ocular modulation transfer function, the spatial arrangement of retinal receptors and the potential acuity of cataract patients.
DNA extracted directly from nodules was used to assess the genetic diversity of Frankia strains symbiotically associated with two species of the genus Casuarina and two of the genus Allocasuarina naturally occurring in northeastern Australia. DNA from field-collected nodules or extracted from reference cultures of Casuarina-infective Frankia strains was used as the template in PCRs with primers targeting two DNA regions, one in the ribosomal operon and the other in the nif operon. PCR products were then analyzed by using a set of restriction endonucleases. Five distinct genetic groups were recognized on the basis of these restriction patterns. These groups were consistently associated with the host species from which the nodules originated. All isolated reference strains had similar patterns and were assigned to group 1 along with six of the eight unisolated Frankia strains from Casuarina equisetifolia in Australia. Group 2 consisted of two unisolated Frankia strains from C. equisetifolia, whereas groups 3 to 5 comprised all unisolated strains from Casuarina cunninghamiana, Allocasuarina torulosa, and Allocasuarina littoralis, respectively. These results demonstrate that, contrary to the results of previous molecular studies of isolated strains, there is genetic diversity among Frankia strains that infect members of the family Casuarinacaeae. The apparent high homogeneity of Frankia strains in these previous studies probably relates to the single host species from which the strains were obtained and the origin of these strains from areas outside the natural geographic range of members of the family Casuarinaceae, where genetic diversity could be lower than in Australia.
The natural biotic capacity of soils to degrade gamma-hexachlorocyclohexane (gamma-HCH, lindane) was estimated using an enrichment technique based on the ability of soil bacteria to develop on synthetic media and degrade the xenobiotic compound, used as the sole source of carbon and energy. Bacterial inocula from relatively highly contaminated soils (from wood treatment factories) were found to promote efficiently the degradation of gamma-HCH, which subsequently permitted isolation of a competent gamma-HCH-degrading microorganism. The decrease of gamma-HCH concurrently with the release of chloride ions and the production of CO2 demonstrated the complete mineralization of gamma-HCH mediated by the isolate. This was confirmed by gas chromatography-mass spectrometry analyses showing that degradation subproducts of gamma-HCH included an unidentified tetrachlorinated compound and subsequently 1,2,4-trichlorobenzene and 2,5-dichlorophenol. The two linA- and linB-like genes coding, respectively, for a gamma-HCH dehydrochlorinase and a dehalogenase were characterized by using a PCR strategy based on sequence homologies with previously published sequences from Sphingomonas paucimobilis UT26. Nucleotide sequence analysis of the linA-like region revealed the presence of a 472-bp open reading frame exhibiting high homology with the linA gene from S. paucimobilis, while a preliminary study also indicated strong homology among the two linB genes. All enzymes involved in the gamma-HCH degradative pathway appear to be extracellular and encoded by genes located on the chromosome, although numerous cryptic plasmids have been detected.
Increasing evidence of acute and chronic ocular effects of ultraviolet (UV) radiation has prompted some manufacturers to develop UV-absorbing rigid and soft contact lens materials. Currently, eight different lenses containing UV-absorbing agents are available in Canada. The spectral transmittance of a sample of these UV-absorbing contact lenses was measured in order to determine if all of them provide adequate protection from wavelengths in the UV spectrum. The sample consisted of 1 lens of each type. Cibasoft Ultrabloc; Permaflex UV; Boston RXD and Equalens; Alberta S; FluoroPerm 30, 60, and 92. A Philips single beam spectrophotometer was used. The lens under test was placed in a silica wet cell filled with unpreserved saline. Spectral transmittance was measured at 0.8-nm intervals over the waveband 200 to 800 nm. The results were recorded by a microcomputer interfaced to the spectrophotometer. The repeatability of spectral transmittance measurements of contact lenses using this method varied between 0% and +/- 1.55% of transmission depending on lens material and wavelength studied. The results showed that none of the rigid gas permeable (RGP) lenses, except the Alberta S, transmitted more than 0.1% (the sensitivity limit of the spectrophotometer) up to 380 nm. The Alberta S exhibited transmittance windows in the UV spectrum with peaks at 270 nm (23%) and 318 nm (29%). The Cibasoft Ultrabloc transmitted less than 1% up to 344 nm, whereas the Permaflex UV had a transmittance window in the waveband 240 to 316 nm with a maximum of 17% at 270 nm.(ABSTRACT TRUNCATED AT 250 WORDS)
PURPOSE: Tonic accommodation contributes to the refractive state of the human eye in the absence of any visual stimulation. As the power of the eye, tonic accommodation level should be a function of wavelength and its variation should constitute a measure of longitudinal chromatic aberration of the eye. METHODS: The level of tonic accommodation was measured with a vernier optometer on a sample of 10 subjects (21-39 years). Five monochromatic filters of wavelengths 450, 486, 550, 600, 656 nm have been used. RESULTS: Results show a tonic accommodation variation with wavelength. The sample mean of longitudinal chromatic aberration (left eye) resulting from the variation of tonic accommodation as a function of wavelength is 1.42 +/- 0.08 D between 450 and 656 nm and 0.96 +/- 0.06 D between 486 and 656 nm. CONCLUSION: These results fit the predictions from theorical models and question previous results.
In order to test the capacity of an optical projection focimeter for simultaneous use by several observers gathered around the instrument, the luminance of the projected target was measured for 3 projection focimeters (model Axil from Essilor, model LP2 from Nikon, and model LM-P5 from Topcon) when the photometer axis was perpendicular to the instrument screen and at oblique angles up to 75 degrees in 5 degrees increments. As expected, the luminance of the target decreased as obliquity of viewing increased; however, the rate of reduction is characteristic of each focimeter model. The repeatability of dioptric measurements with the Axil focimeter was assessed in the usual viewing position when the luminance of the target was reduced by optical filters (neutral density varying from 0.2 to 1 in 0.2 steps). The repeatablity remains within +/- 0.05 D for optical densities < or = 0.8. Our results show that a useful luminance is maintained over an observation angle that extends to 45 degrees. Depending on the model of focimeter, several observers may simultaneously observe and judge the focusing of the instrument.
The back optic zone radius of soft contact lenses cannot be measured with conventional methods used for rigid lenses. Although a variety of techniques has been proposed, none has received wide clinical acceptance. A study was conducted to determine the precision and limitations of a method using a Zeiss keratometer. A total of 192 lenses from categories 1 (Optima 38) and 4 (Hydrocurve II 55%) of the FDA classification were used. These lenses were divided into six groups according to their water content and refractive power. The difference versus the mean of two different measurements (repeatability) has been plotted to determine the bias (mean of the differences relative to zero), the 95% limits of agreement and the repeatability coefficient of the technique. Variation between measurements was also assessed by calculating the reproducibility coefficient R for each soft lens. The precision expressed by the SD of a series of ten measurements on one lens in each group, was computed for comparison with previous studies. The repeatability of the technique expressed in term of 95% limits of agreement (range +/- 0.058 to +/- 0.198 mm) meets the American Standards Tolerances for each group of soft lenses studied. The coefficient of reproducibility R for each soft lens studied seems to be related to lens flexibility and dioptric power. The technique used gives the same degree of precision as other keratometric methods described in previous studies. The clinical use of this method is discussed with regard to practical factors.
Among the Frankia strains capable of establishing a nitrogen-fixing symbiosis with actinorrhizal plants, in planta sporangial formation is not universal and has led to the distinction between spore-positive (Sp+) and spore-negative (Sp-) nodules. Numerous Frankia strains have been isolated in pure culture from Sp+ nodules of different host plants, but, although they were able to reinfect their respective host plant, none of them was able to differentiate endophytic sporangia under laboratory conditions. The first step of this study was to demonstrate, at the molecular level, the existence of specific Sp+ strain genotypes differing from Sp- strain genotypes in a single alder stand. In a second step, by way of PCR amplification and sequencing of the PCR products, we have characterized oligonucleotide primers specific for the genus Frankia and for each of the two types of Frankia microsymbionts able, or not, to differentiate sporangia inside natural green alder nodules. These primers applied in PCRs with DNA extracted from nodules confirmed the morphological identification and revealed the presence of nodules colonized by both types of actinomycetes. Finally, a preliminary PCR study was conducted with DNA extracted directly from soil samples which permitted checking the rhizosphere of Sp+ and Sp- nodules for the presence of the corresponding strains.
Levels of impairment and disability determine eligibility for different welfare programs for visually handicapped persons. General eye care practitioners have to determine the level of impairment for administrative purposes, whereas the low-vision practitioner measures the level of impairment in order to plan the rehabilitation program. We compared the severity of visual impairment reported by the referring practitioners and the one reported by the low-vision specialists for the population of elderly low-vision patients receiving care from one of the largest rehabilitation centers for the visually handicapped in Quebec. Visual acuity ratings reported by general practitioners are lower than those reported by low-vision practitioners. The presence of visual handicap is generally well identified but the severity of visual impairment according to the World Health Organization (WHO)'s categories is not properly gauged by the general eye care practitioners as expressed by the sensitivity and the positive predictive value of the classification of the general practitioners in respect to the classification of the low-vision optometrists. The need to use existing standardized methods to measure visual acuity (VA) is emphasized. It may be hypothesized that this overestimation of the severity of the visual condition may have a negative impact on the process of rehabilitation of the elderly.
Investigations to quantify bacterial survival and DNA persistence of a genetically engineered population of Escherichia coli introduced into soil microcosms were carried out. The survival of E. coli was monitored by plate counting and immunofluorescence methods, whereas the persistence of the DNA was evaluated by using a most-probable-number-polymerase chain reaction method. Whereas the E. coli population density declined below the plate-counting-technique detection threshold (10(2) CFU.g-1) after 15 days, 10(3) extracellular and 5 x 10(5) total DNA target sequences were still detected after 40 days. Additionally, the E. coli cell counts fell below the detection limit of the immunofluorescence method (10(5) cells.g-1) before the end of the experiment. Colony hybridizations did not reveal gene transfer to the indigenous microflora. These results confirm the persistence of residual E. coli target sequences that could not be detected by the classical cell counting method and offer promising applications for the environmental detection of microorganisms, either engineered, pathogenic, or released for beneficial effects.
The organisation of ribosomal RNA-encoding (rrn) genes has been studied in Frankia sp. strain ORS020606. The two rrn clusters present in Frankia strain ORS020606 were isolated from genomic banks in phage lambda EMBL3 by hybridization with oligodeoxyribonucleotide probes. The 5'-3' gene order is the usual one for bacteria: 16S-23S-5S. The two clusters are not distinguishable by restriction enzyme mapping inside the coding section, but vary considerably outside it. Sequencing showed that the 16S-rRNA-encoding gene of ORS020606 is very closely related to that of another Alnus-infective Frankia strain (Ag45/Mut15) and highly homologous to corresponding genes of Streptomyces spp. Two possible promoter sequences were detected upstream from the 16S gene, while no tRNA-encoding gene was detected in the whole operon. Regions with a high proportion of divergence for the study of phylogenetic relationships within the genus were looked for and found in the first intergenic spacer, in the 23S and in the 16S gene.
DNA sequences from the intergenic spacer (IGS) region of the ribosomal operon were amplified by the polymerase chain reaction (PCR) technique using two primers derived from 16S and 23S rRNA conserved sequences. The PCR products, cleaved by 4 base cutting restriction enzymes, were used to differentiate Nitrobacter strains. This method offered a convenient alternative to serological testing for characterization of Nitrobacter isolates and enabled a large number of strains to be genotypically characterized easily and rapidly. This method was successfully used to characterize natural populations of Nitrobacter from various soils and a lake. A diversity was demonstrated in various soils, and in a lake both in freshwater and in sediments. Strains closely related to both WL and LL were found in these ecosystems. It seems that the diversity of Nitrobacter populations was not associated with global environments but may be related to the presence of locally coexisting niches.
The complete nucleotide sequence of the nifD gene encoding the alpha subunit of component I of nitrogenase from Frankia alni strain ArI3 was determined. The coding region is 1,458 bp in length and encodes a polypeptide of 486 residues with a predicted molecular weight of 53,500. Phylogenetic inferences with 12 complete published nifD sequences were drawn using a variety of approaches. Frankia nifD clusters with proteobacteria rather than with Clostridium pasteurianum, the other Gram-positive bacterium studied. Extant eubacterial nif genes seem to have at least three distinct evolutionary origins as a result of ancient gene duplications. Within the Gram-positive bacterial phylum, functional nif genes descend from different duplicates.
Pupil centration is important to the optical blur on the retina. Using a dual Maxwellian view system we measured the centration of the pupil with respect to the achromatic axis of the eye as a function of pupil size. Significant shifts of the pupil center (up to 0.6 mm) with pupil dilation were measured in both nasal and temporal directions. The effect was usually symmetrical between the two eyes and the shift was linear with pupil size in one-half of the subjects. From their initial positions the linear pupil center shifts with dilation were in the direction of the achromatic axis.
An automated 2-rod stereoacuity test was modified to permit lateral head movement during testing so that depth perception by means of motion parallax could be assessed. The patient, a 48-year-old truck driver with one blind eye, found the test easy to perform. In 24 presentations of a 40 sec arc disparity he was 96% correct. With the same number of presentations at 20 sec arc he was 83% correct. In the latter case, the probability of success by chance alone was p = 0.0004.
Equivalent viewing power (EVP), field of view, and working distance (WD) were calculated for 4 different magnifier equivalent powers, four magnifier-to-eye distances, and for uncorrected spherical ametropias varying from +20.00 to -20.00 D in 0.25 D steps. Results show that the various viewing conditions which arise (depending on whether or not the refractive correction is worn) can differ considerably. The uncorrected unaccommodating myope has a greater EVP than the equivalent power of the magnifier if he chooses a magnifier-to-eye distance shorter than the focal length of the magnifier. In this situation, field of view is also enhanced. The uncorrected unaccommodating hyperope using a magnifier-to-eye distance longer than the focal length of the magnifier achieves a stronger EVP than the equivalent power of the magnifier. However, field of view is then reduced. For the uncorrected unaccommodating spherical ametrope, the use of a magnifier-to-eye distance corresponding to the focal length of the magnifier seems to be a good compromise between EVP, field of view, and working distance.