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Biomedical subjects

P Auger

Publications and source records attributed to P Auger.

At least 37 records · Page 2Linked to original sources
PubMed1998

Fast game theory coupled to slow population dynamics: the case of domestic cat populations.

We study a deterministic model of a population where individuals alternatively adopt hawk and dove tactics. It is assumed that the hawk and dove individuals compete for some resources at a fast time scale. This fast part of the model is coupled to a slow part that describes the growth of the population. It is shown that, in a constant game matrix, the population grows according to a logistic curve whose r and K parameters are related to the payoff of the tactics. Results show that the highest population density is obtained when all individuals are dove. We also study a density-dependent game matrix for which the gain is a function of the population density. In this case, we show that two stable equilibria can occur, a first one at low density with a high proportion of hawk individuals and a second one at large density with a low proportion of hawk individuals. Our model is applied to domestic cat populations for which the behavior of individuals in competition with one another can be modeled by two tactics: hawk and dove. Such tactics change with density of population. The results of the model agree well with observed data: high-density populations of domestic cats are mainly doves, whereas low-density populations are mainly hawks.

Animals↗
PubMed1998

A two-patch model of Gambian sleeping sickness: application to vector control strategies in a village and plantations.

A compartmental model is described for the spread of Gambian sleeping sickness in a spatially heterogeneous environment in which vector and human populations migrate between two "patches": the village and the plantations. The number of equilibrium points depends on two "summary parameters": gr the proportion removed among human infections, and R0, the basic reproduction number. The origin is stable for R0 < 1 and unstable for R0 > 1. Control strategies are assessed by studying the mix of vector control between the two patches that bring R0 below 1. The results demonstrate the importance of vector control in the plantations. For example if 20 percent of flies are in the village and the blood meal rate in the village is 10 percent, then a 20 percent added vector mortality in the village must be combined with a 9 percent added mortality in the plantations in order to bring R0 below 1. The results are quite insensitive to the blood meal rate in the village. Optimal strategies (that minimize the total number of flies trapped in both patches) are briefly discussed.

Communicable Disease Control↗
PubMed1997

Influence of individual aggressiveness on the dynamics of competitive populations.

Two populations are subdivided into two categories of individuals (hawks and lows). Individuals fight to have access to a resource which is necessary for their survival. Conflicts occur between individuals belonging to the same population and to different populations. We investigate the long term effects of the conflicts on the stability of the community. The model is a set of ODE's with four variables corresponding to hawk and dove individuals of the two populations. Two time scales are considered. A fast time scale is used to describe frequent encounters and fightings between individuals trying to monopolize the resource. A slow time scale is used for the demography and the long term effects of encounters. We use aggregation methods in order to reduce this model into a system of two ODE's only for the total densities of the two populations which is found to be a classical Lotka-Volterra competition model. We study different cases of proportions of hawks and doves in both populations on the global coexistence and the mutual exclusion of the two populations. Pure dove tactics in both populations are unstable. In cases of mixed hawk and dove in both populations, there is coexistence. Pure dove or mixed hawk-dove tactics in one population can coexist with pure hawks in the other one when the costs of fightings between hawks are large enough.

Aggression↗
PubMed1997

Epidemiological study of Candida spp. colonization in cardiovascular surgical patients.

Candida infections involve multiple risk factors. Among the independent risk factors identified, the degree of colonization of Candida spp. allows the prediction of subsequent severe candidosis in surgical patients. The aim of this study was to assess among 13 selected variables, those that would best predict the perioperative variation of the colonization index (CI) of Candida spp. in cardiovascular surgical patients. The colonization index took into account the number of sites colonized and the density of growth. The results showed that 56.8% of our patients were colonized perioperatively. A total of 116 isolates were identified and Candida albicans accounted for 76.7% of the strains. Among the patients who developed post-surgical Candida infections, 57.1% had an increase of the CI early after the operation. By univariate analysis, three factors were significantly associated with an increase of the CI in patients after surgery; sex (female), the duration of central intravascular catheterization and the length of stay in the surgical intensive care unit (SICU). Epidemiological data could help predict those patients who are at risk of developing Candida infections.

Aged↗
PubMed1997

Perioperative variation in phagocytic activity against Candida albicans measured by a flow-cytometric assay in cardiovascular-surgery patients.

Candidiasis is an opportunistic fungal infection that frequently occurs following modifications of host defenses. Major surgery can be responsible for such alterations, and therefore it increases the risk of fungal infection. The purpose of this study was to evaluate the perioperative impairment of leukocyte function in patients after cardiovascular surgery by measuring the phagocytic activity against Candida albicans by a flow-cytometric method. The average postsurgical decrease in phagocytosis in our patients was 11.4%. By univariate analysis, three factors, all related to antibiotic therapy, were significantly associated with an important decrease in phagocytosis; the use of antimicrobial therapy before surgery, the number of different antibiotics taken, and the length of antibiotic treatment. The results of our study showed that the use of antibiotics in patients undergoing cardiovascular surgery alters the normal phagocytic activity of the host immune system against C. albicans and that flow cytometry is a rapid and simple technique that helps in early identification of patients at high risk for Candida infections. The mechanisms by which surgery and antibiotics decrease phagocytosis remain to be elucidated.

Adult↗
PubMed1996

Emergence of population growth models: fast migration and slow growth.

We present aggregation and emergence methods in large-scale dynamical systems with different timescales. Aggregation corresponds to the reduction of the dimension of a dynamical system which is replaced by a smaller model for a small number of global variables at a slow timescale. We study the couplings between fast and slow dynamics leading to the emergence of global properties in the aggregated model. First, we study the case of a single population in a patchy environment. Growth rates are assumed to be linear on each patch. Individuals can migrate from one patch to another at a fast timescale. We choose different density dependent migration processes. In each case, we use aggregation methods to obtain the corresponding growth equation for the total density of the population at a slow timescale. We look for particular density dependent migration processes leading to an aggregated logistic-like equation. Second, we study the case of two interacting populations. A particular choice of density dependent migrations leads to an aggregated competition model.

Animals↗
PubMed1996

Candida albicans serotype analysis by flow cytometry.

Candida albicans strains can be assigned to either of two major serogroups, A or B. Antigenic surface determinants present only in serotype A strains allow such a distinction, which has epidemiologic relevance. Reports have established that the relative distributions of the two serotypes can vary depending on the geographic origin of the isolates. A prevalence of susceptibility to an antifungal agent, flucytosine, was also observed with isolates of serotype A. More recently, it was suggested that the occurrence of serotype B isolates in various clinical forms of candidiasis is increasing. However, this latest finding remains controversial since serotyping results vary widely from one laboratory to another because of the lack of standardized methodologies. Difficulty in interpretation of results, which may lead to erroneous serotype identification, is the major setback associated with current methods. For this study, we thus devised a procedure that relies on flow cytometry and that may eliminate ambiguities in serotype determination. The validation of results was achieved with two types of serotype A-specific antisera, Iatron Factor 6 antiserum and an anti-C. albicans antiserum adsorbed on serotype B yeast cells. Agreement between results obtained with these two reagents was 100% with a wide array of Candida strains. These results confirmed the potential of the flow cytometric procedure as a reliable and reproducible method to establish the serotypes of C. albicans strains. Furthermore, some applications of this procedure to the epidemiological study of this human pathogen are presented.

Candida albicans↗
PubMed1993

Application of biotyping and DNA typing of Candida albicans to the epidemiology of recurrent vulvovaginal candidiasis.

One-hundred and five Candida albicans isolates from various anatomic sites of 28 patients, obtained at the onset of two consecutive episodes of well-documented recurrent vulvovaginitis, were typed by methods relying on physiologic or genomic markers. The isolates represented a wide variety of types, and neither a single biotype nor genotype was associated with recurrent vaginitis or a particular body site. Patients generally carried similar strains at various anatomic sites that persisted over time. Genomic methods indicated an 86% rate of relapse, which suggested that most recurrent vaginal infections are of endogenous origin. A similar evaluation with biotyping methods was inconclusive because of a lack of reproducibility, resulting from clonal variation or switching, and difficulties in establishing the number of phenotypic tests necessary to distinguish between identical and different strains. Therefore, Southern hybridization was considered the ideal reference method to study the epidemiology of C. albicans infections.

Adolescent↗
PubMed1993

Muramidase-mediated damage to Candida yeast cells. Histochemical and immunochemical characterization of accumulating wall-like material.

Hen egg-white lysozyme is known to be fungicidal to blastoconidia of Candida albicans under defined in vitro conditions. This lethal action leads to changes in the layering of cell wall and to plasmolysis, caused by unremitting accumulation of wall-like material between the yeast cell wall and cytoplasmic membrane. Here, several methods were applied on ultrathin sections to define the nature of wall-like material: histochemical staining with periodic acid-thiocarbohydrazide-silver proteinate, periodic acid-alkaline bismuth, and phosphotungstic acid at low pH; the localization of the carbohydrate residues with lectin-gold complex; immunocytochemical staining with monospecific antibodies, factor 1 and 6, which recognized major cell wall antigens. The wall-like material was almost uniformly highlighted with periodic acid-thiocarbohydrazide-silver proteinate, factor 1 antibody, concanavalin A-gold and wheat germ agglutinin-ovomucoid-gold, indicating the presence of mannoproteins and chitin. The serotype A-specific epitope recognized by factor 6 antibody was not detected in the wall-like material, although it was demonstrated in the outer cell wall layers after 2 h of exposure to lysozyme.

Antibodies, Monoclonal↗
PubMed1992

Growth factors and cell kinetics: a mathematical model applied to Il-3 deprivation on leukemic cell lines.

We assume the existence of a specific G1 protein which is an initiator of DNA replication. This initiator is supposed to be synthesized according to Michaelis-Menten kinetics. In order to start DNA replication, it is assumed that this G1 specific protein must be produced in a required amount. Intra-cellular growth inhibitors and extra-cellular growth factors control the production of the initiator. This model allows to calculate the average G1 phase time as a function of the various chemical concentrations of nutrients, enzymes, growth inhibitors and growth factors. This model is compared to cell kinetics experiments on a leukemic cell line responding to Interleukin 3 deprivation. The curves giving the experimental average G1 phase times with respect to Interleukin-3 concentrations are fitted by the mathematical model with a quite good agreement.

Cells, Cultured↗
PubMed1992

Interpretation of epicardial mapping by means of computer simulations: applications to calcium, lidocaine and to BRL 34915.

The aim of this work was to compare experimental investigations on effects of lidocaine, calcium and, BRL 34915 on reentries to simulated data obtained by use of a model of propagation based on the Huygens' construction method already described in previous works. Calcium and lidocaine effects are investigated on anisotropic conduction conditions. In both cases, reduction in conduction velocities are observed. In lidocaine case, a refractory area is located along the longitudinal axis. In agreement with experimental electrical mapping, the simulations show that the stabilization of reentrant excitation is mainly due to the existence of this refractory area around which the reentrant circuit can develop. The experimental study shows that BRL 34915 has both arrhythmogenic and antiarrhythmic effects. A detailed electrophysiological analysis has shown that drug infusion act on normal cardiac cells by decreasing the relative and absolute refractory period. BRL 34915 action is simulated by a decrease in the refractory period showing that the time frequency of the reentrant activity is increased and that the spatial size where the reentry is developing is becoming smaller. These two effects are arrhythmogenic, the simulated data being so in good agreement with the experimental ones.

Animals↗
PubMed1992

A multicenter, open comparative study of parenteral cefotaxime and ceftriaxone in the treatment of nosocomial lower respiratory tract infections.

A multicenter Canadian study enrolled 74 persons to compare low-dose cefotaxime at 1 g every 8 hr to ceftriaxone 1 g every 12 hr in patients with nosocomial pneumonia. Of 57 evaluable patients (30 cefotaxime and 27 ceftriaxone) in this preliminary report, 93% responded to therapy in both groups. Ceftriaxone patients tended to have more side effects (14.2%). This study is continuing to accrue patients to achieve 100 evaluable patients. Interim data, however, support the continued use of low-dose cefotaxime as an appropriate alternative for clinically effective and cost-effective management of nosocomially acquired pneumonia.

Adult↗
PubMed1991

Cell walls of normal and lysozyme-damaged blastoconidia of Candida albicans: localization of surface factor 4 antigen and vicinal-glycol staining.

The fungicidal effect of lysozyme on Candida albicans involves ultrastructural modifications previously described (G. Marquis, S. Montplaisir, S. Garzon, H. Strykowski, and P. Auger, Lab. Invest. 46:627-636, 1982). To further define the action of lysozyme on the yeast cell wall, we used the following: (i) the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method to highlight vicinal-glycol-reactive sites of complex carbohydrates; (ii) a monospecific antiserum and a protein A-gold complex to study the expression of surface factor 4, a major Candida antigen; and (iii) the periodic acid-silver methenamine method to stain cell wall glycoproteins. All Candida cells were found to express surface factor 4 antigen. In normal blastoconidia, surface factor 4 was located in a glycoprotein-rich cell wall layer, underneath radially oriented bundles of filaments which form the outermost wall layer. In lysozyme-treated blastoconidia, this glycoprotein-rich layer was lost and the regular brushlike organization of the outer fibrillogranular layer was disrupted. PA-TCH-SP staining and localization of surface factor 4 antigen demonstrated an altered arrangement of bundles of filaments in the outer wall layers of blastoconidia which were morphologically intact but had abnormal cell wall appearance. Next, there was a reduction in thickness of the outer layer and the expression of surface factor 4 antigen was limited to the cytoplasmic membrane area. Later on, the cell wall was almost uniformly highlighted by PA-TCH-SP staining. These data evinced a highly plastic architecture of the cell wall in C. albicans.

Antigens, Fungal↗
PubMed1990

Incidence of occult athlete's foot in swimmers.

Athlete's foot is a dermatophytic infection frequently found in adults. This disease is, in some cases, asymptomatic. In order to evaluate the incidence of subclinical infection, we obtained 300 toe-web samples from the fourth interdigital space of 150 regular swimmers. More over, 66 specimens from the pool area were analysed. The method used was the carpet technique described by Mariat et al. (10). The fungal isolates were identified according to standard methods. A list of epidemiological data was completed for every swimmer. In our results, 22 swimmers had positive cultures (15%), 8 of these cases had no lesions (36%). They included 7 infections with Trichophyton mentagrophytes (87.5%) and one with T. rubrum (12.5%). We observed one case with a dual infection. Only one sample from the inanimate environment was positive. This study showed a significant incidence of occult athlete's foot in swimmers. To control this endemic problem, adequate preventive measures must be taken.

Adolescent↗
PubMed1990

Double-blind comparison of pefloxacin and cefazolin as prophylaxis in elective cardiovascular surgery.

A total of 162 patients (134 males and 28 females) scheduled for coronary artery bypass grafting (144) or valve surgery (18) were randomly assigned to receive, under double-blind conditions, either pefloxacin 400 mg iv or cefazolin 1.0 g 30 min before the surgical incision and then post-operatively 12-hourly x 4 or 6-hourly x 8, respectively. Positive per- and post-operative cultures were seen in 27 patients (11 pefloxacin, 16 cefazolin) and 47 micro-organisms were isolated: 34 per-operatively (21 pefloxacin, 13 cefazolin) and 13 post-operatively (4 pefloxacin, 9 cefazolin). There were five failures of prophylaxis (2 pefloxacin, 3 cefazolin): two early (less than 5 days: 1 pefloxacin, 1 cefazolin) and three late (greater than or equal to 5 days, 1 pefloxacin, 2 cefazolin) divided into (i) one major primary failure in the cefazolin group (1 cefazolin resistant Staphylococcus epidermidis mediastinitis); (ii) two minor primary failures, one in each group (Gram-positive sternal incision abscesses) and (iii) two secondary failures (1 cefazolin resistant Enterobacter cloacae and Pseudomonas aeruginosa UTI in the cefazolin group and one culture negative pneumonia in the pefloxacin group). Tolerance to both antibiotics was excellent. In our sample of patients, the efficacy and safety of pefloxacin was not different from those of cefazolin in prophylaxis in cardiovascular surgery.

Aged↗
PubMed1990

Interest of biotyping Candida albicans in chronic vulvovaginitis.

Chronic vulvovaginitis due to Candida albicans is a major clinical problem for the physician. Although new antifungal drugs are now available, the therapeutic approach of this disease remains disappointing. The aims of this study were two-fold. First, we wanted to evaluate the reliability of a single sampling performed by most clinicians in verifying if the yeast infects the entire genital mucosa or a preferential site and, second, to biotype the strains recovered in order to see if more than one strain are responsible for the infection. We found, in 18 patients suffering from vaginal candidosis, that the entire genital mucosa was infected by the yeast and the strain recovered from the different genital sites in a single patient was the same in 100% of the cases. Only 1.4% of the samples were negative. In addition, we biotyped the strains obtained from the gastrointestinal tract of these patients to evaluate this site as a potential source of infection. We obtained gastrointestinal tract samples for 15 of the 18 patients and we could identify C. albicans in 100% of the cases. Furthermore, 73.3% of the patients harboured the same strains of C. albicans in the gastrointestinal tract as in the vagina.

Adult↗