Biomedical subjects

Frederick L Schuster

Publications and source records attributed to Frederick L Schuster.

23 records · Page 2Linked to original sources

PubMed2002

Cultivation of Babesia and Babesia-like blood parasites: agents of an emerging zoonotic disease.

Babesia and its close relatives are members of a group of organisms called piroplasms, a name which comes from their pear-shaped outlines. Long associated with blood diseases of cattle and other mammals, members of the genus Babesia have been recognized since the 1950s as infectious agents in humans. Species of this protozoan blood parasite that have routinely been isolated from mice (B. microti) or cattle (B. divergens) have also been isolated from humans. In addition to these familiar species, new isolates that resist being placed in existing taxonomic categories are the basis for rethinking their phylogenetic relationships based on sequencing data. The parasite represents a threat to the safety of the blood supply in that blood from asymptomatic humans can transmit Babesia to blood recipients. Such transmissions have occurred. The development of methods for cultivation of these organisms represents a significant opportunity to study their biology and disease potential. In addition, in vitro cultivation has provided a basis for studying immune responses of mammals to these infectious agents, with the hope of ultimately producing attenuated strains that could be used for immunizing of cattle and, perhaps, humans who live in areas of endemicity. The microaerophilous stationary phase culture technique, which uses a tissue culture medium base supplemented with appropriate serum and erythrocytes, has made it possible to obtain large numbers of parasitized erythrocytes for studying the biology of this parasite.

Animals↗

PubMed2002

Cultivation of clinically significant hemoflagellates.

The hemoflagellates, Trypanosoma spp. and Leishmania spp., are causal agents of a number of parasitic diseases having a major impact on humans and domestic animals over vast areas of the globe. Among the diseases are some of the most pernicious and deadly of human afflictions: African sleeping sickness, Chagas' disease, kala-azar, and Oriental sore. The organisms have complex, pleomorphic life cycles typically involving a vertebrate and an invertebrate host, the latter serving as a vector. In the vertebrate host, they are primarily blood and tissue parasites. In their transition from one host to another, the hemoflagellates undergo morphological, physiological, and biochemical changes that facilitate their growth and subsequent transmission. A major goal in the study of the hemoflagellates has been the cultivation in vitro of both vertebrate and invertebrate stages of the organisms. The first types of media used in their cultivation, and still useful for establishment of cultures, were undefined and contained a complex of ingredients. These gave way to semidefined formulations which included tissue culture media as a base and, as a next step, addition of tissue culture cells as a feeder layer to promote parasite growth. More recently developed media are completely defined, having replaced the feeder cells with various supplements. Serum, a sometimes-variable component of the media, can be replaced by various serum substitutes. This review focuses on the hemoflagellates that infect humans, describing stages in the development of media leading to the fully defined formulations that are now available for the cultivation of many of these organisms.

Animals↗

PubMedDate not supplied

Isolation of a thermotolerant Paravahlkampfia sp. from lizard intestine: biology and molecular identification.

An amoeba was isolated from the intestines of several moribund pink-tongued skinks (lizards), Hemisphaeriodon gerrardi. Unusual features of this isolate were its ability to grow at temperatures of > or = 37 degrees C, and its inability to use Escherichia coli as a food source or to grow axenically on a variety of enriched culture media suitable for other soil amoeba isolates. Growth was abundant, however, on tissue culture cells, with amoebae clearing cell monolayers in approximately 48 h at 37 degrees C. Trophozoites had a vahlkampfiid-like morphology, moving by means of an anterior eruptive pseudopod. Cysts, round to slightly ovoid and lacking exit pores, were formed in culture. Tests for enflagellation of trophic amoebae were negative. Indirect immunofluorescence staining was negative for Naegleria fowleri and Willaertia sp. The isolate was sensitive to azithromycin, but not to amphotericin B, pentamidine isethionate, fluconazole, 5-fluorocytosine, and sulfadiazine. Phylogenetic analysis based on the PCR-amplified small subunit ribosomal DNA, identified the organism as Paravahlkampfia ustiana, an amoeba not previously isolated from either poikilothermic or homeothermic hosts. No evidence of pathology was seen in stained sections of lizard intestine, suggesting that the ameba was part of the normal fauna of the lizard gut. Its diet in the lizard intestine is unknown and the organism may have unusual growth requirements. Thus, P. ustiana joins other soil amoebae that have been isolated from mammals, amphibia, fish, and reptiles, which have the potential of becoming opportunistic pathogens.

Amoeba↗

PubMedDate not supplied

Morphologic and molecular identification of Naegleria dunnebackei n. sp. isolated from a water sample.

Naegleria dunnebackei n. sp., a new species of the free-living amoeboflagellate Naegleria, is described in this report. The organism was isolated from a water sample taken from drinking troughs associated with cases of primary amoebic meningoencephalitis in cattle at a ranch in southern California. The isolate grew at, but not above 37 degrees C, and did not kill young mice upon intranasal inoculation suggesting that it was not pathogenic. The new species combines morphological features of non-pathogenic Naegleria gruberi and pathogenic Naegleria fowleri. The trophic amoeba resembled other members of the genus, with a prominent vesicular nucleus and mitochondria with discoidal cristae; a Golgi apparatus was not observed by electron microscopy. The cyst stage had pores in the wall typical of those seen in pathogenic N. fowleri. Upon suspension in distilled water, amoebae transformed into temporary, non-feeding flagellates, mostly with two anterior flagella but occasionally with four. The rationale for its description as a new species was based upon sequencing of the 5.8S rDNA and internal transcribed spacers of the amoeba, which is similar to but not identical to that of Naegleria gallica, differing from that organism's DNA by six base pairs. Virus-like elements were found in the cytoplasm of trophic amoebae, often in association with crystalloids, and may be the cause of lysis of amoebae in culture.

Animal Husbandry↗

PubMedDate not supplied

In-vitro activity of miltefosine and voriconazole on clinical isolates of free-living amebas: Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri.

The anticancer agent miltefosine and the antifungal drug voriconazole were tested in vitro against Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri. All three amebas are etiologic agents of chronic (Balamuthia, Acanthamoeba) or fulminant (Naegleria) encephalitides in humans and animals and, in the case of Acanthamoeba, amebic keratitis. Balamuthia exposed to <40 microm concentrations of miltefosine survived, while concentrations of >or=40 microM were generally amebacidal, with variation in sensitivity between strains. At amebastatic drug concentrations, recovery from drug effects could take as long as 2 weeks. Acanthamoeba spp. recovered from exposure to 40 microM, but not 80 microM miltefosin. Attempts to define more narrowly the minimal inhibitory (MIC) and minimal amebacidal concentrations (MAC) for Balamuthia and Acanthamoeba were difficult due to persistence of non-proliferating trophic amebas in the medium. For N. fowleri, 40 and 55 microM were the MIC and MAC, respectively, with no trophic amebas seen at the MAC. Voriconazole had little or no inhibitory effect on Balamuthia at concentrations up to 40 microg/ml, but had a strong inhibitory effect upon Acanthamoeba spp. and N. fowleri at all drug concentrations through 40 microg/ml. Following transfer to drug-free medium, Acanthamoeba polyphaga recovered within a period of 2 weeks; N. fowleri amebas recovered from exposure to 1 microg/ml, but not from higher concentrations. All testing was done on trophic amebas; drug sensitivities of cysts were not examined. Miltefosine and voriconazole are potentially useful drugs for treatment of free-living amebic infections, though sensitivities differ between genera, species, and strains.

Acanthamoeba↗