Towards a model of host-parasite relationships

The question asked in this article is: "what is a parasite?". Defining a parasite requires defining its host at the same time. A difficult question therefore arises about host-parasite relationships. The object of general parasitology is in fact to study the relationship between a host and its parasite. The initial question "what is a parasite?" has to be reformulated within a conceptual framework, that of "relationship". This article is an attempt to transpose into parasitology some concepts which have been profitable in the fields of physics and chemistry. The studies of R. Thom about the individual are also used. Concepts like that of field and principles like that of minimization are probably operational on a high level of organization. The description of host-parasite relationships could benefit from these concepts.

In vitro pharmacodynamic parameters of sordarin derivatives in comparison with those of marketed compounds against Pneumocystis carinii isolated from rats

Pneumocystis carinii pneumonia remains one of the most serious complications of immunosuppressed patients. In this study, the in vitro pharmacodynamic parameters of four sordarin derivatives (GM 191519, GM 237354, GM 193663, and GM 219771) have been evaluated by a new quantitative approach and compared with the commercially available drugs pentamidine, atovaquone, and trimethoprim-sulfamethoxazole (TMP-SMX). In vitro activities and in vivo therapeutic efficacies of sordarin derivatives against P. carinii were also evaluated. In vitro activity was determined by the broth microdilution technique, comparing the total number of microorganisms in treated and drug-free cultures by using Giemsa staining. The in vitro maximum effect (E(max)), the drug concentrations to reach 50% of E(max) (EC(50)), and the slope of the dose-response curve were then estimated by the Hill equation (E(max) sigmoid model). Sordarin derivatives were the most potent agents against P. carinii, with EC(50)s of 0.00025, 0.0007, 0.0043, and 0. 025 microg/ml for GM 191519, GM 237354, GM 193663, and GM 219771, respectively. The EC(50)s of pentamidine, atovaquone, and TMP-SMX were 0.025, 0.16, and 26.7/133.5 microg/ml, respectively. The results obtained with this approach showed GM 237354 and GM 191519 to be approximately 35- and 100-fold more active in vitro than pentamidine, the most active marketed compound. All sordarin derivatives tested were at least 5,000-fold more active in vitro than TMP-SMX. The three sordarin derivatives tested in vivo-GM 191519, GM 237354, and GM 219771-showed a marked therapeutic efficacy, defined as reduction of cyst forms per gram of lung. GM 191519 was the most potent (daily dose reducing 50% of the P. carinii burden in the lungs [ED(50)], 0.05 mg/kg/day) followed by GM 237354 and GM 219771 (ED(50)s, 0.30 and 0.49 mg/kg/day, respectively). Good agreement between in vitro parameters and in vivo outcome was obtained when P. carinii pneumonia in rats was treated with sordarin derivatives.

Current in vitro culture systems for Pneumocystis

Although Pneumocystis continuous culture systems have not yet been developed, efficient short-term in vitro methods allowing the production of infectious forms of Pneumocystis can now be employed. The quality of the inoculum will influence the in vitro development of P. carinii. For this reason, efficient extraction and cryopreservation techniques are considered in this section. In vitro growth and limited passage were obtained by inoculating freshly extracted parasites onto fibroblast- or epithelial-like cell monolayers cultivated in ordinary tissue culture flasks, culture plates, microcarrier beads or other culture devices. Cultures were usually maintained in an atmosphere of 5% CO2 at 35-37 degrees C. The results obtained in these different systems were surprisingly similar: the number of parasites increased about 6-10 times within the first 3-4 days post-inoculation, then remained stationary until day 7-14 and decreased rapidly. If passages were attempted, the growth decreased gradually and no growth was recorded after 2-3 passages. Proof of the in vitro Pneumocystis attachment to feeder cells has been furnished by electron microscopy. Two currently used feeder cell culture systems were selected in this subchapter. The first system is a co-culture of monolayer lung epithelial-like cells with Pneumocystis. After trypsin treatment and passage of cells with attached parasites to culture bottles containing fresh medium, 3 or more new culture bottles can be plated. A 2-4-fold increase in parasite number can be obtained but, interestingly, cultured parasites were more infectious to the nude rat than freshly extracted lung parasites. In the second system, the spinner flask culture method, Pneumocystis is cultivated on cell coated microbeads in slow stirring vessels, in order to exploit the beads' huge surface where microorganisms can transiently adhere and grow and from where they can be easily detached by simply leaving the beads to settle down. This culture system has ensured 10(8)-10(9) viable trophozoites in each harvest after 7-10 days of slow stirring incubation.

[Epidural lipomatosis: complication of long-term corticotherapy. Apropos of 2 cases]

Spinal epidural lipomatosis (SEL) is defined as the deposition of loose fat tissue in the epidural space. Two cases are reported which illustrate the main features of this uncommon disease. Most frequently SEL is revealed by neurologic manifestations such as an acute chronic spinal cord compression. Corticosteroid therapy and obesity are the main factors able to induce the disease. The common location of the SEL at the thoracic spine is explained by the physiologic abundance of fat and by the relative narrowness of the spinal canal at this level. An osteoporotic vertebral crush fracture which reduces the diameter of the canal frequently reveals the SEL. MRI confirms the diagnosis of SEL and shows the extent in the spinal canal. The treatment of SEL is difficult. The decrease or the stop of corticosteroid therapy has allowed the recovery in a few cases with chronic neurologic symptoms. The risks of a surgical procedure are important in these patients and the medical or surgical treatment should be discussed taking into account the clinical symptoms of SEL, its location and extent, and the risks of recurrence if corticosteroid therapy must go on.

The blood-stages of Plasmodium georgesi, P. gonderi and P. petersi: course of untreated infection in their natural hosts and additional morphological distinctive features

In the blood of a Cercocebus albigena and of a C. galeritus agilis monkey, the infection with Plasmodium gonderi was found to follow its well-known chronic course; P. georgesi seemed to occur as a relapsing type of malaria parasite; P. petersi was found for only a few days and at a low level in C. albigena (end of an attack?). As shown by using polarized light, the pigment granules appeared mostly as fine dots in P. georgesi, short rods in P. gonderi and long needles in P. petersi. The three species can be distinguished by the morphological appearance of the nucleus of the young trophozoites, and also by the measurement of its surface area (Sa): small round nucleus (Sa = 0.81 +/- 0.06 microns 2) in P. gonderi, large 2-coloured nucleus (Sa = 1.43 +/- 0.21 microns 2) in P. petersi, and long crescent-shaped nucleus (Sa = 2.18 +/- 0.25 microns 2) in P. georgesi. The first colour illustrations of the blood-stages of P. georgesi are presented. The dynamics of single and mixed blood infections in primate malaria parasites are discussed, with a proposal to classify them into 3 types.

Pneumocystitis carinii organisms from in vitro culture are highly infectious to the nude rat

Many in vitro systems have been used to cultivate Pneumocystis, but only limited parasite growth has been obtained by different authors. A reliable in vitro system enabling a sustained propagation of Pneumocystis appears to be an important condition for a better definition of the transmission of P. carinii pneumonia. In this work, Pneumocystis in vitro culture was performed on monolayers of L2 rat lung epithelial-like cells. Ultrastructural assessment revealed that culture parasites were structurally intact. Pneumocystis culture samples were intratracheally inoculated into corticosteroid-treated nude rats (nonlatently infected by P. carinii), which developed P. carinii pneumonia at 40 days postinoculation. The infectious power of parasites obtained in vitro was 7-10 times higher than that of parasites freshly extracted from parasitized rat lung. In summary, the present results show that it is possible to obtain in vitro highly infectious Pneumocystis forms, and this study provides a promising infectivity test for use by investigators working on Pneumocystis in vitro systems.

Kinetic study of antifungal activity of amphotericin B, 5-fluorocytosine and ketoconazole against clinical yeast isolates using liquid-phase turbidimetry

The fungal growth of clinical yeast isolates and of VW32 clone of Candida albicans were measured in vitro using a liquid-phase turbidimetric system (Bioscreen from Labsystems, France) in defined conditions. Cultures were performed in Shadomy's liquid medium and the fungal growth automatically evaluated every 10 minutes for 24 hours using various concentrations of drugs. The system made it possible to test 200 culture samples in one experiment. Yeast sensitivity to drugs was also measured by using our routine semi-automatic turbidimetric system. We observed that kinetic patterns of activity of each antifungal agent were typical. The in vitro tests showed that of 927 clinical yeast isolates 99.2% were sensitive to amphotericin B, 94.4% to 5-fluorocytosine and 69.7% to ketoconazole.

Individual evolution of digestive tract colonization of holoxenic mice by Candida albicans

Oral administration of various concentrations of Candida albicans to 6-day-old mice established colonization of the digestive tract without mortality. After being weaned (day 21), the development of colonization was studied in a group of mice by daily counting of the number of CFU contained in the feces of each animal. Two features concerning the development of colonization were noted. The course of colonization in individual mice was highly erratic and lead to either transitory or sometimes long-lasting colonization. These results show the importance of a dynamic study of colonization, a condition necessary for any experimental study.

[Effect of glucose and nitrogen concentrations on the morphology of Candida albicans and the formation of chlamydospores in synthetic culture media]

Candida albicans was grown in the darkness, at 28 degrees C, in a synthetic medium in which glucose and nitrogen concentrations were varied. Numeric appraisal of the chlamydospore index was possible only in the medium where glucose concentration was 0,08 g/1 or less. When the glucose concentration raised, pseudomycelial thalli bore numerous chlamydospores but sometimes also chains of cells with a dense granular content. These thalli bud yeast cells which separate and bud again in the medium. The different morphological aspects of the cultures are decribed, illustrated and classified according to the glucose and nitrogen concentration of the medium.

[Chlamydosporulation in "Candida albicans". Course of the morphogenesis; influence of light and sowing density (author's transl)]

Candida albicans is cultivated on rice cream decoction with glucose for chlamydospore production. A developmental stage refered as readiness is recognized. At this stage, the pseudomycelial thalli are able to produce chlamydospore in water without further stimulus by the sporulation medium. The greater the inoculum, the earlier appears the readiness. During the growth phase up to the readiness, the light is inhibiting the chlamydosporulation and favorising the yeast development. After the readiness, light still inhibits chlalmydospore formation.

[Chlamydosporulation in "Candida albicans": influence of sowing density and glucose, nitrogen, biotin and mineral salts concentration in rice-cream decoction (author's transl)]

Chlamydospore production by Candida albicans was investigated in rice cream decoction inoculated with a blastospore suspension. Effects of glucose, KH2PO4, (NH4)2SO4 and biotin addition were estimated using a "chlamydospore index" i.e. the mean-number of mature chlamydospores produced from a single blastospore development. If no other component was added, it appeared that better sporulation was obtained with both glucose concentration and inoculum size optimum (0.5 g/l and 7.8 X 10(3) blastospores/ml respectively). In glucose-KH2PO4 enriched medium, chlamydosporulation was the best with 0.5 g/l glucose and 0.5 g/l KH2PO4. The addition of biotin reduced the chlamydospore index at the concentrations tested (0.6 to 20 microgram/l). When glucose and (NH4)2SO4 were added together, it seemed that one of the C or N component had to be in low concentration for a good sporulation. The action of salts was also investigated; and finally a synthetic medium is proposed. The improvement of this medium is now in progress.

[Study of the Sporothrix schenkii (yeast forms) extract. Electrophoretic and immunoelectrophoretic analyses: characterization of enzymatic activities]

An extract from living yeast forms of S. schenckii was prepared. The yeasts originated from a shake culture in B.H.I. broth (Difco) incubated for 3 days at 35 degrees C in darkness; they were harvested, washed and disrupted with glass beads in a model MSK Braun mechanical cell homogenizer; a freezing-thawing was added to improve the extract. After electrophoretic separation in agarose gel, the extract's components were characterized by their enzymic activity; with this technique, 30 bands were revealed. These enzymic activities were also investigated on the antigenic fractions of the extract revealed by a rabbit hyperimmunserum: 16 among 22 immunoprecipitates are identified by their catalytic properties. Study of the earliest precipitating antibodies (appearing-order and enzymic caracterization) in rabbits just immunized completes this work. How to ameliorate the quality of the extract by culture and extraction conditions is also specified.

[Growth and sexual reproduction of the dermatophyte Arthroderma vanbreuseghemii Takashio (Trichophyton mentagrophytes (Robin blanchard) on a synthetic medium]

A synthetic medium without agar is proposed for the growth and the sexual reprpduction of the dermatophyte Arthroderma vanbreuseghemii (Trichophyton mentagrophytes). The determinations of mycelium dry weight showed that this species grew poorly with only one amino-acid as nitrogen source. A. vanbreuseghemii grew weakly on a mixture of glutamic and aspartic acid and serin. A small amount of aromatic amino-acids added to this mixture, increased the growth rate comparable to that obtained on peptone. The sexual reproduction was induced on synthetic medium with a propicious balance between carbon and nitrogen sources. Addition of 0.5 or 1g/1 of glucose to 50 mg N/1 supplied by the amino-acids mixture (including the aromatics) gave the optimal ratio. Using these conditions, many cleistothecia was produced by crossing two semi-compatible strains.

Congenital coxa vara, patella aplasia and tarsal synostosis: a new inherited syndrome

A kindred is described with a probably new inherited syndrome, involving bilateral congenital hip dysplasia with coxa vara, patella aplasia and tarsal synostosis. This association is probably inherited as an incomplete dominant trait, apparently as a result of a new mutation.

In this case a single pleiotropic gene might be held responsible for the multiple skeletal defects.

From a bibliographical review, it may be concluded that the nosological association of these multiple defects has never been published so far.