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Biomedical subjects

D T John

Publications and source records attributed to D T John.

At least 19 recordsLinked to original sources
PubMed2000

A light microscopy study of the migration of Naegleria fowleri from the nasal submucosa to the central nervous system during the early stage of primary amebic meningoencephalitis in mice.

The migratory pathway of Naegleria fowleri from the nasal submucosa to the central nervous system (CNS) during the early stage of primary amebic meningoencephalitis (PAM) was investigated in mice. Twenty-one-day-old CD-1 mice were inoculated by intranasal instillation of 1 x 10(6) amebas. Animals were divided into 3 groups of 5 and, after being anesthetized, were killed at intervals of 24, 32, and 48 hr postinoculation by transcardial perfusion with formaldehyde, acetic acid, and methanol. The heads were decalcified, divided in the midsagittal plane, and the area of the cribriform plate removed and embedded in paraffin. Serial sections were cut at 8 microm and stained with a combination of celestin blue, Harris' hematoxylin, and acid fuchsin for light microscopy. Focal inflammation and amebas were observed in the submucosal nerve plexus, olfactory nerves penetrating the cribriform plate, and the olfactory bulb of the brain as early as 24 hr postinoculation. The time periods selected assured that the disease process would not obliterate soft tissue structures. Earlier studies used moribund mice in which the inflammation and the number of amebas were overwhelming. The present study provides convincing evidence that amebas gain initial access to the CNS through olfactory nerves within the cribriform plate during the early stages of PAM.

Amebiasis↗
PubMed1997

Amebicidal activity of wild animal serum.

The sera of 16 species of wild animals representing 5 classes of vertebrates were assayed for amebicidal activity against species of Naegleria. The greatest activity was observed for sera of bullfrogs, muskrats, and raccoons, all of which are animals associated with water. In contrast, the sera from animals such as toads, box turtles, sparrows, and squirrels exhibited minimal or no amebicidal activity. In general, pathogenic Naegleria tended to be less susceptible than nonpathogenic Naegleria to the lytic effect of raccoon serum. Heat-inactivated serum was not amebicidal, suggesting that perhaps complement may be involved in the serum-mediated lysis of amebas.

Amebiasis↗
PubMed1996

Viability of pathogenic Acanthamoeba and Naegleria and virulence of N. fowleri during long-term cryopreservation.

This is a followup report on the viability of pathogenic Acanthamoeba castellanii, Naegleria australiensis, and N. fowleri during 5 years of cryopreservation and the virulence of N. fowleri during 30 months of cryostorage, all at -70 degrees C. The greatest decrease in viability occurred during the first year of freezing and was 10-fold greater than the average yearly decrease during years 2-5. At 5 years of cryostorage viability was 33% for A. castellanii, 38% for N. fowleri and 51% for N. australiensis. Virulence of N. fowleri did not decrease during 30 months of freezing and what appeared to be an increase in virulence during cryopreservation may be the result of reduced viability of the less virulent amebae in a culture.

Acanthamoeba↗
PubMed1996

Techniques for isolating thermotolerant and pathogenic freeliving amebae.

Several conditions of isolation were evaluated to determine which yielded the greatest number of thermotolerant and pathogenic freeliving amebae. Swab samples, easier to obtain and process, produced more pathogenic amebae than water samples. If water samples are required, 50-ml volumes gave the greatest percentage of pathogenic isolates. An incubating temperature of 42 degrees C yielded the most thermotolerant amebae. A total of 11 pathogenic isolates were obtained from 762 environmental samples and were Acanthamoeba (55%), Naegleria fowleri Carter, 1970 (27%), and N. australiensis De Jonckheere, 1981 (18%).

Acanthamoeba↗
PubMed1995

Seasonal distribution of pathogenic free-living amebae in Oklahoma waters.

Pathogenic free-living amebae cause serious human disease, including infection of the eye and the central nervous system. The purpose of this study was to sample aquatic environments in the Tulsa, Oklahoma, area year-round for the presence of these disease-causing amebae. A total of 34 pathogenic isolates were obtained from 2,016 processed water and swab samples. Pathogenicity was determined by the ability of amebae to cause death in mice after intranasal inoculation. Pathogenic amebae were isolated during every month of the year and were identified as Naegleria australiensis (38%), Acanthamoeba species (35%), N. fowleri (18%), and leptomyxid amebae (9%). Pathogenic leptomyxids have not previously been reported from the environment. The greatest percentage of recovery of pathogens occurred during the spring and autumn. The prevalence of pathogenic free-living amebae in the sampled waters was 1 pathogen/3.4 l water.

Acanthamoeba↗
PubMed1995

Reduction in virulence of Naegleria fowleri following growth with cholesterol.

It has been reported that the virulence of axenically cultivated Entamoeba histolytica increases following growth with cholesterol. The purpose of this study was to determine whether cholesterol would enhance the virulence of axenically cultivated Naegleria fowleri. Amoebae were cultivated in axenic medium with (100 micrograms/ml) or without cholesterol for 6 months and tested in mice for changes in virulence. After 6 months of continuous cultivation. N. fowleri grown with cholesterol was less virulent for mice than the same strain grown without cholesterol.

Animals↗
PubMed1994

Cryopreservation of pathogenic free-living amebae.

A variety of conditions of cryopreservation were evaluated in order to define a single procedure for freezing the amebae of pathogenic Naegleria and Acanthamoeba. The average best conditions for freezing the three species studied were: 1 x 10(6) exponentially growing amebae/ml of freezing medium consisting of 12% dimethylsulfoxide, 20% heat-inactivated bovine calf serum, 4% glucose, in Mix ameba medium; 30 min equilibration at 23 degrees C (room temperature), followed by 60 min at -20 degrees C, with storage at -70 degrees C. Under these conditions viability after 1 month of freezing was 53% for Acanthamoeba castellanii, 64% for Naegleria fowleri, and 66% for Naegleria australiensis. After 12 months of freezing, viability was 39% for A. castellanii, 47% for N. fowleri, and 53% for N. australiensis.

Acanthamoeba↗
PubMed1994

Enhancement of virulence of Naegleria fowleri by growth in Vero-cell cultures.

The virulence of Naegleria fowleri for mice decreases with prolonged maintenance in axenic culture. Would the virulence be affected if amebas were grown in African green-monkey kidney (Vero)-cell cultures rather than in axenic culture? The weakly virulent LEE strain of N. fowleri was cultivated with Vero cells for 6 mo and tested in mice for changes in virulence. We found that continuous growth in Vero-cell cultures enhanced the virulence of the LEE strain and we propose that, as an alternative to serial passage in mice, the virulence of weakly virulent strains of N. fowleri may be enhanced by maintenance in Vero-cell cultures.

Amebiasis↗
PubMed1993

Virulence of Naegleria fowleri affected by axenic cultivation and passage in mice.

The virulence of Naegleria fowleri decreases with prolonged axenic cultivation. The decline in virulence of highly virulent, mouse-passaged LEE strain amebae was monitored during 5 years of continuous axenic cultivation. The most rapid decrease in virulence occurred during the first 2 years. Virulence could be restored to original levels by 3 serial passages in mice. The composition of axenic media also affected the virulence of N. fowleri, with a more enriched medium appearing to restore some of the virulence of a weakly virulent strain.

Animals↗
PubMed1991

Flagella number among Naegleria flagellates.

Scanning electron microscopy was used to determine the number of flagella on the flagellates of Naegleria australiensis, N. fowleri, N. gruberi, and N. jadini. Although the majority of flagellates had 2 flagella, there was considerable variation among individual cells. The number of flagella per flagellate varied from 1-8, with 2.4 being the average number per cell. For the different species, the average number of flagella per cell ranged from 2.0 in N. jadini to 3.1 for N. australiensis. The greatest amount of variation occurred in N. australiensis, with only 43% of the cells having 2 flagella. By contrast, 92% of N. fowleri cells had 2 flagella. Naegleria jadini and N. gruberi were intermediate with 80% and 74% biflagellates, respectively.

Animals↗
PubMed1990

Susceptibility of wild mammals to infection with Naegleria fowleri.

Animals of 4 families of small wild mammals were live-trapped and inoculated intranasally with Naegleria fowleri to determine patterns of susceptibility. Of the 7 species of animals examined, only rodents were susceptible to N. fowleri. Susceptible animals were eastern gray squirrel, hispid cotton rat, muskrat, and house mouse. Mammals that were not susceptible at a dose of 10(6) were opossum, raccoon, and eastern cottontail rabbit. Perhaps rodents and humans share a common anatomical or physiological determinant that makes them susceptible to infection with N. fowleri.

Amebiasis↗
PubMed1990

Mammalian cell cultures affected by Naegleria gruberi.

Amebae of 8 strains of Naegleria gruberi were able to destroy 10 established mammalian cell lines including lung, kidney, ovary, connective tissue, neuroblastoma, and laryngeal and cervical carcinoma cells. The strains of N. gruberi varied in their ability to produce a destructive effect (DE) in African green monkey kidney (Vero) cell cultures. However, cell line susceptibility was found to be equivalent when tested with the considerably destructive 1518/l strain of N. gruberi. The Vero cell line proved to be a useful indicator culture for assessing the destructive potential of N. gruberi strains. Other factors affecting the extent of DE produced were ameba to mammalian cell ratio and the length of time that amebae were maintained in cell culture.

Animals↗
PubMed1989

Cytopathogenicity of Naegleria fowleri in mammalian cell cultures.

A total of 13 strains of Naegleria fowleri were cytopathogenic for lung, kidney, foreskin, ovary, connective tissue, neuroblastoma, laryngeal carcinoma, and cervical carcinoma mammalian cell lines. The strains of N. fowleri varied considerably in their ability to produce a cytopathic effect (CPE). Likewise, the different mammalian cell lines exhibited varying degrees of susceptability to the cytopathogenicity of the amebae. The African green-monkey kidney (Vero) cell line proved to be useful for assessing the cytopathogenic potential of N. fowleri strains. Although one strain failed to produce CPE in Vero-cell cultures, it did so in the two neuroblastoma cell lines. Other factors affecting the extent of CPE produced were incubation temperature, ameba: mammalian cell ratio, and the length of time during which amebae were maintained in cell culture.

Animals↗
PubMed1988

Intranasal immunization of mice against Naegleria fowleri.

The purpose of this research was to determine whether mice could be protected from lethal challenge with Naegleria fowleri by prior intranasal exposure to pathogenic and nonpathogenic Naegleria. Mortality ranged from 0 to 100% for mice inoculated intranasally (i.n.) with 5 x 10(3) amebae of 13 human isolates of N. fowleri. Mice were immunized and challenged i.n. using live amebae of strains of low, medium, and high virulence. The greatest protection against lethal challenge was afforded by three immunizing doses of 10(3) amebae per dose of the strain of medium virulence. Nonpathogenic N. gruberi also was used to immunize mice i.n. against lethal challenge with N. fowleri. Protection was greater following immunization with N. gruberi than it was after immunization with N. fowleri, suggesting that nonpathogenic N. gruberi may be a better immunogen in protecting mice against lethal naeglerial challenge.

Administration, Intranasal↗
PubMed1986

Conditions for maximum enflagellation in Naegleria fowleri.

Ameba to flagellate transformation in Naegleria fowleri (Lovell strain) was affected by growth temperature, phase of growth, strain of ameba, culture agitation, enflagellation temperature, enflagellation diluent, and cell concentration. Amebae transformed best when they were grown without agitation and enflagellated with agitation. Regardless of growth temperature (23 degrees, 30 degrees, 37 degrees, and 42 degrees C were tested), amebae transformed best at 37 degrees C. Enflagellation was greatest for cells harvested between 24 h (mid-exponential) and 84 h (late stationary) of growth.

Amoeba↗
PubMed1986

Trypanosoma cruzi from wild raccoons in Oklahoma.

Trypomastigotes of Trypanosoma cruzi were detected in the blood of 5 of 8 wild adult raccoons which were live-trapped in Tulsa, Okla. Organisms were isolated in diphasic blood agar medium and maintained in Vero cell cultures. Inoculated mice exhibited transient parasitemias without tissue involvement. Amastigote forms occurred within Vero cells. This is the first report of naturally occurring T cruzi infection of wild mammals in Oklahoma.

Animals↗
PubMed1985

Amebostomes of Naegleria fowleri.

The strain of ameba, culture incubation temperature, and phase of ameba growth affected the number of amebostomes present on amebae of Naegleria fowleri. Serial passage of N. fowleri through mice decreased the average number of amebostomes. Amebostomes were shown to be functional by their ability to engulf yeast cells.

Amoeba↗