The pathogenicity of soil amebas

Can Acanthamoeba Harbor Monkeypox Virus?

Acanthamoeba is well known to host a variety of microorganisms such as viruses, bacteria, protozoa, and yeast. Given the recent number of cases of monkeypox infection, we speculate that amoebae may be aiding viral transmission to the susceptible hosts. Although there is no confirmatory evidence to suggest that Acanthamoeba is a host to monkeypox (a double-stranded DNA virus), the recent discovery of mimivirus (another double-stranded DNA virus) from Acanthamoeba, suggests that amoebae may shelter monkeypox virus. Furthermore, given the possible spread of monkeypox virus from animals to humans during an earlier outbreak, which came about after patients came in contact with prairie dogs, it is likely that animals may also act as mixing vessel between ubiquitously distributed Acanthamoeba and monkeypox virus, in addition to the environmental habitat that acts as an interface in complex interactions between diverse microorganisms and the host.

Biological characteristics and pathogenicity of Acanthamoeba

Acanthamoeba is an opportunistic protozoa, which exists widely in nature and is mainly distributed in soil and water. Acanthamoeba usually exists in two forms, trophozoites and cysts. The trophozoite stage is one of growth and reproduction while the cyst stage is characterized by cellular quiescence, commonly resulting in human infection, and the lack of effective monotherapy after initial infection leads to chronic disease. Acanthamoeba can infect several human body tissues such as the skin, cornea, conjunctiva, respiratory tract, and reproductive tract, especially when the tissue barriers are damaged. Furthermore, serious infections can cause Acanthamoeba keratitis, granulomatous amoebic encephalitis, skin, and lung infections. With an increasing number of Acanthamoeba infections in recent years, the pathogenicity of Acanthamoeba is becoming more relevant to mainstream clinical care. This review article will describe the etiological characteristics of Acanthamoeba infection in detail from the aspects of biological characteristic, classification, disease, and pathogenic mechanism in order to provide scientific basis for the diagnosis, treatment, and prevention of Acanthamoeba infection.

Trogocytosis in Unicellular Eukaryotes

Trogocytosis is a mode of internalization of a part of a live cell by nibbling and is mechanistically distinct from phagocytosis, which implies internalization of a whole cell or a particle. Trogocytosis has been demonstrated in a broad range of cell types in multicellular organisms and is also known to be involved in a plethora of functions. In immune cells, trogocytosis is involved in the "cross-dressing" between antigen presenting cells and T cells, and is thus considered to mediate intercellular communication. On the other hand, trogocytosis has also been reported in a variety of unicellular organisms including the protistan (protozoan) parasite Entamoeba histolytica. E. histolytica ingests human T cell line by trogocytosis and acquires complement resistance and cross-dresses major histocompatibility complex (MHC) class I on the cell surface. Furthermore, trogocytosis and trogocytosis-like phenomena (nibbling of a live cell, not previously described as trogocytosis) have also been reported in other parasitic protists such as Trichomonas, Plasmodium, Toxoplasma, and free-living amoebae. Thus, trogocytosis is conserved in diverse eukaryotic supergroups as a means of intercellular communication. It is depicting the universality of trogocytosis among eukaryotes. In this review, we summarize our current understanding of trogocytosis in unicellular organisms, including the history of its discovery, taxonomical distribution, roles, and molecular mechanisms.

Biting Off What Can Be Chewed: Trogocytosis in Health, Infection, and Disease

Trogocytosis is part of an emerging, exciting theme of cell-cell interactions both within and between species, and it is relevant to host-pathogen interactions in many different contexts. Trogocytosis is a process in which one cell physically extracts and ingests "bites" of cellular material from another cell. It was first described in eukaryotic microbes, where it was uncovered as a mechanism by which amoebae kill cells. Trogocytosis is potentially a fundamental form of eukaryotic cell-cell interaction, since it also occurs in multicellular organisms, where it has functions in the immune system, in the central nervous system, and during development. There are numerous scenarios in which trogocytosis occurs and an ever-evolving list of functions associated with this process. Many aspects of trogocytosis are relevant to microbial pathogenesis. It was recently discovered that immune cells perform trogocytosis to kill Trichomonas vaginalis parasites. Additionally, through trogocytosis, Entamoeba histolytica acquires and displays human cell membrane proteins, enabling immune evasion. Intracellular bacteria seem to exploit host cell trogocytosis, since they can use it to spread from cell to cell. Thus, a picture is emerging in which trogocytosis plays critical roles in normal physiology, infection, and disease.

Clinical presentations, genotypic diversity and phylogenetic analysis of Acanthamoeba species causing keratitis

Introduction. Acanthamoeba keratitis is a sight-threatening corneal infection that is commonly reported among contact lens users and those suffering from corneal trauma. The prevalence of Acanthamoeba species or genotypes in causing keratitis infection is not well known.Aim. This study was conducted to identify and genotype Acanthamoeba isolates from keratitis patients, targeting the ribosomal nuclear subunit (Rns) region, and describe the associated clinical presentation and treatment outcome.Methodology. Thirty culture-confirmed patients with Acanthamoeba keratitis, identified in a tertiary eye care centre in South India during the period from December 2016 to December 2018, were included in this study. The data collected from patient records include demographic details, history of illness, mode of trauma, treatment history and follow-up status. The genotype and species were identified based on the Rns sequence and phylogenetic tree analysis.Results. Acanthamoeba culbertsoni was the most predominant keratitis-causing species, followed by Acanthamoeba quina, Acanthamoeba castellanii, Acanthamoeba healyi, Acanthamoeba hatchetti, Acanthamoeba polyphaga and Acanthamoeba stevensoni. Three major genotypes were identified (T4, T11 and T12), with the T4 genotype being the most predominant, with four subclusters, i.e. T4A, T4B, T4D and T4E. This is the first report on corneal infection by the A. stevensoni T11 genotype and the A. healyi T12 genotype. No significant correlation was observed between the clinical outcomes of corneal disease and the genotypes or species.Conclusion. Rns genotyping is very effective in identifying the Acanthamoeba species and genotype in keratitis. Genotyping of Acanthamoeba spp. will help to advance our understanding of genotype-specific pathogenesis and geographical distribution.

Excretory and Secretory Proteins of Naegleria fowleri Induce Inflammatory Responses in BV-2 Microglial Cells

Naegleria fowleri, a free-living amoeba that is found in diverse environmental habitats, can cause a type of fulminating hemorrhagic meningoencephalitis, primary amoebic meningoencephalitis (PAM), in humans. The pathogenesis of PAM is not fully understood, but it is likely to be primarily caused by disruption of the host's nervous system via a direct phagocytic mechanism by the amoeba. Naegleria fowleri trophozoites are known to secrete diverse proteins that may indirectly contribute to the pathogenic function of the amoeba, but this factor is not clearly understood. In this study, we analyzed the inflammatory responses in BV-2 microglial cells induced by excretory and secretory proteins of N. fowleri (NfESP). Treatment of BV-2 cells with NfESP induced the expression of various cytokines and chemokines, including the proinflammatory cytokines IL-1α and TNF-α. NfESP-induced IL-1α and TNF-α expression in BV-2 cells were regulated by p38, JNK, and ERK MAPKs. NfESP-induced IL-1α and TNF-α production in BV-2 cells were effectively downregulated by inhibition of NF-kB and AP-1. These results collectively suggest that NfESP stimulates BV-2 cells to release IL-1α and TNF-α via NF-kB- and AP-1-dependent MAPK signaling pathways. The released cytokines may contribute to inflammatory responses in microglia and other cell types in the brain during N. fowleri infection.

Taking a bite: Amoebic trogocytosis in Entamoeba histolytica and beyond

Entamoeba histolytica is a diarrheal pathogen with the ability to cause profound host tissue damage. This organism possesses contact-dependent cell killing activity, which is likely to be a major contributor to tissue damage. E. histolytica trophozoites were recently shown to ingest fragments of living human cells. It was demonstrated that this process, termed amoebic trogocytosis, contributes to cell killing. Recent advances in ex vivo and 3-D cell culture approaches have shed light on mechanisms for tissue destruction by E. histolytica, allowing amoebic trogocytosis to be placed in the context of additional host and pathogen mediators of tissue damage. In addition to its relevance to pathogenesis of amoebiasis, an appreciation is emerging that intercellular nibbling occurs in many organisms, from protozoa to mammals.

Chew on this: amoebic trogocytosis and host cell killing by Entamoeba histolytica

Entamoeba histolytica was named 'histolytica' (from histo-, 'tissue'; lytic-, 'dissolving') for its ability to destroy host tissues. Direct killing of host cells by the amoebae is likely to be the driving factor that underlies tissue destruction, but the mechanism was unclear. We recently showed that, after attaching to host cells, amoebae bite off and ingest distinct host cell fragments, and that this contributes to cell killing. We review this process, termed 'amoebic trogocytosis' (trogo-, 'nibble'), and how this process interplays with phagocytosis, or whole cell ingestion, in this organism. 'Nibbling' processes have been described in other microbes and in multicellular organisms. The discovery of amoebic trogocytosis in E. histolytica may also shed light on an evolutionarily conserved process for intercellular exchange.

Balamuthia mandrillaris in South America: an emerging potential hidden pathogen in Perú

Balamuthia mandrillaris is a free living amoeba that can be isolated from soil. It is an emerging pathogen causing skin lesions as well as CNS involvement with a fatal outcome if untreated. Further, infections can sometimes can also appear in peripheral areas such as extremities (usually knee), or trunk. Moreover, it often progresses to an infiltrative lesion that occasionally becomes ulcerated. In countries like Peru, a skin lesion will precede other symptoms. This primary cutaneous lesion can be present for weeks or even months. However, the appearance of neurological disease predicts a poor prognosis. Diagnosis requires a high level of suspicion.

Risk for transmission of Naegleria fowleri from solid organ transplantation

Primary amebic meningoencephalitis (PAM) caused by the free-living ameba (FLA) Naegleria fowleri is a rare but rapidly fatal disease of the central nervous system (CNS) affecting predominantly young, previously healthy persons. No effective chemotherapeutic prophylaxis or treatment has been identified. Recently, three transplant-associated clusters of encephalitis caused by another FLA, Balamuthia mandrillaris, have occurred, prompting questions regarding the suitability of extra-CNS solid organ transplantation from donors with PAM. During 1995-2012, 21 transplant recipients of solid organs donated by five patients with fatal cases of PAM were reported in the United States. None of the recipients developed PAM, and several recipients tested negative for N. fowleri by serology. However, historical PAM case reports and animal experiments with N. fowleri, combined with new postmortem findings from four patients with PAM, suggest that extra-CNS dissemination of N. fowleri can occur and might pose a risk for disease transmission via transplantation. The risks of transplantation with an organ possibly harboring N. fowleri should be carefully weighed for each individual recipient against the potentially greater risk of delaying transplantation while waiting for another suitable organ. In this article, we present a case series and review existing data to inform such risk assessments.

Induction of interleukin-8 by Naegleria fowleri lysates requires activation of extracellular signal-regulated kinase in human astroglial cells

Naegleria fowleri is a pathogenic free-living amoeba which causes primary amoebic meningoencephalitis in humans and experimental animals. To investigate the mechanisms of such inflammatory diseases, potential chemokine gene activation in human astroglial cells was investigated following treatment with N. fowleri lysates. We demonstrated that N. fowleri are potent inducers for the expression of interleukin-8 (IL-8) genes in human astroglial cells which was preceded by activation of extracellular signal-regulated kinase (ERK). In addition, N. fowleri lysates induces the DNA binding activity of activator protein-1 (AP-1), an important transcription factor for IL-8 induction. The specific mitogen-activated protein kinase kinase/ERK inhibitor, U0126, blocks N. fowleri-mediated AP-1 activation and subsequent IL-8 induction. N. fowleri-induced IL-8 expression requires activation of ERK in human astroglial cells. These findings indicate that treatment of N. fowleri on human astroglial cells leads to the activation of AP-1 and subsequent expression of IL-8 which are dependent on ERK activation. These results may help understand the N. fowleri-mediated upregulation of chemokine and cytokine expression in the astroglial cells.

The significance of hand wash compliance on the transfer of dermal lipids in contact lens wear

AIM

The aim of this study was to assess the impact of hand washing regimes on lipid transference to contact lenses. The presence of lipids on contact lenses can affect visual acuity and enhance spoilation. Additionally, they may even mediate and foster microbial transfer and serve as a marker of potential dermal contamination.

METHODS AND MATERIALS

A social hand wash and the Royal College of Nursing (RCN) hand wash were investigated. A 'no-wash regime' was used as control. The transfer of lipids from the hand was assessed by Thin Layer Chromatography (TLC). Lipid transference to the contact lenses was studied through fluorescence spectroscopy (FS).

RESULTS

Iodine staining, for presence of lipids, on TLC plates indicated the 'no-wash regime' score averaged at 3.4±0.8, the social wash averaged at 2.2±0.9 and the RCN averaged at 1.2±0.3 on a scale of 1-4. The FS of lipids on contact lenses for 'no washing' presented an average of 28.47±10.54 fluorescence units (FU), the social wash presented an average of 13.52±11.12 FU and the RCN wash presented a much lower average 6.47±4.26 FU.

CONCLUSIONS

This work demonstrates how the method used for washing the hands can affect the concentration of lipids, and the transfer of these lipids onto contact lenses. A regime of hand washing for contact lens users should be standardised to help reduce potentially transferable species present on the hands.

The immune response toNaegleria fowleriamebae and pathogenesis of infection

The genus Naegleria is comprised of a group of free-living ameboflagellates found in diverse habitats worldwide. Over 30 species have been isolated from soil and water but only Naegleria fowleri (N. fowleri) has been associated with human disease. Naegleria fowleri causes primary amebic meningoencephalitis (PAM), a fatal disease of the central nervous system. The pathogenesis of PAM and the role of host immunity to N. fowleri are poorly understood. Strategies for combating infection are limited because disease progression is rapid and N. fowleri has developed strategies to evade the immune system. The medical significance of these free-living ameboflagellates should not be underestimated, not only because they are agents of human disease, but also because they can serve as reservoirs of pathogenic bacteria.

Production of Nfa1-specific monoclonal antibodies that influences the in vitro cytotoxicity of Naegleria fowleri trophozoites on microglial cells

Naegleria fowleri, agent of fatal primary amoebic meningoencephalitis, appears to induce cytotoxicity mechanically through its contact with the cell. The nfa1 gene cloned from a cDNA library of pathogenic N. fowleri by immunoscreening consists of 360 bp and expresses a 13.1-kDa recombinant protein (rNfa1) that demonstrated localization in the pseudopodia when examined using immunocytochemistry. To study the mechanisms involved in N. fowleri cytotoxicity, we developed a large volume of rNfa1-specific monoclonal antibody (McAb) against a 17-kDa His-tag fusion rNfa1 protein using a cell fusion technique. We established eight McAb-producing hybridoma cells. The antibodies were all immunoglobulin G2b and reacted strongly with a 17-kDa band representing the rNfa1 fusion protein in Western blotting, demonstrating immunoreactivity to the Nfa1 protein in pseudopodia (especially in the food cups) of N. fowleri trophozoites. A 51Cr-release assay indicated N. fowleri cytotoxicity by demonstrating that it eliminated 37.8, 60.6, and 98.8% of the target (microglial) cells 6, 12, and 24 h after co-incubation, respectively. When an anti-Nfa1 McAb was added to the coculture system, N. fowleri cytotoxicity decreased to 29.8, 44.1, and 66.3%, respectively.

Primary amebic meningoencephalitis: a silent killer

One week after swimming in a man-made lake, a 9-year-old boy presented to the emergency department with headache, vomiting and lethargy. He had neck pain upon flexion and was unable to stand or walk. Cerebrospinal fluid examination revealed trophozoite and diflagellate forms consistent with Naegleria fowleri, an ameba species known to cause primary amebic meningoencephalitis. Despite aggressive management with amphotericin B and rifampin, he died 2 days later. This case report describes the clinical presentation, diagnostic findings and management of this uncommon but lethal entity.

Cytopathic changes and pro-inflammatory cytokines induced by Naegleria fowleri trophozoites in rat microglial cells and protective effects of an anti-Nfa1 antibody

Naegleria fowleri, a free-living amoeba, causes fatal primary amoebic meningoencephalitis in experimental animals and humans. The nfa1 gene (360 bp) was previously cloned from a cDNA library of pathogenic N. fowleri by immunoscreening, and produced a 13.1-kDa recombinant protein that showed pseudopodia-specific localization by immunocytochemistry. On the basis of an idea that the pseudopodia-specific Nfa1 protein seems to be involved in the pathogenicity of N. fowleri, the cytopathic activity of N. fowleri trophozoites co-cultured with rat microglial cells was observed, and the effects of an anti-Nfa1 antibody in a co-culture system were elucidated. Using light, scanning and transmission electron microscopy, it was seen that N. fowleri trophozoites in contact with microglial cells produced vigorous pseudopodia and a food-cup structure. Microglial cells were destroyed by N. fowleri trophozoites as seen from necrotic cell death in a time-dependent manner. In a(51)Cr release assay, N. fowleri showed 17.8%, 24.9%, 54.6% and 98% cytotoxicity against microglial cells at 3, 6, 12 and 24 h post-incubation, respectively. However, when anti-Nfa1 antibody was added in a coculture system, N. fowleri cytotoxicity was reduced to 15.5%, 20.3%, 46.7% and 66.9%, respectively. Moreover, microglial cells co-cultured with N. fowleri trophozoites secreted the pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-6. In the presence of anti-Nfa1 antibody, the secretion of TNF-alpha was slightly, but not significantly, decreased.

Role of the Nfa1 protein in pathogenic Naegleria fowleri cocultured with CHO target cells

Naegleria fowleri, a free-living amoeba, exists as a virulent pathogen which causes fatal primary amoebic meningoencephalitis in experimental animals and humans. Using infected and immune mouse sera, we previously cloned an nfa1 gene from a cDNA library of N. fowleri by immunoscreening. The nfa1 gene (360 bp) produced a recombinant 13.1-kDa protein, and the Nfa1 protein showed pseudopodium-specific immunolocalization on a trophozoite of N. fowleri. In this study, the role of the Nfa1 protein as a cell contact mechanism of N. fowleri cocultured with target cells was observed by an immunofluorescence assay with an anti-Nfa1 polyclonal antibody. Using confocal microscopic findings, the Nfa1 protein was located on the pseudopodia of N. fowleri trophozoites. The Nfa1 protein in N. fowleri trophozoites cocultured with CHO target cells was also located on pseudopodia, as well as in a food cup formed as a phagocytic structure in close contact with target cells. The amount of nfa1 mRNA of N. fowleri was strongly increased 6 h after coculture.

Amoebicidal activity of multipurpose contact lens solutions

PURPOSE

To compare the amoebicidal activity of two commercially available multipurpose contact lens care systems, by using cyst and trophozoite growth of two strains each of Acanthamoeba castellanii and Acanthamoeba polyphaga.

METHODS

Trophozoites and cysts of Acanthamoeba species, isolated from corneal ulcers and an ATCC strain, were exposed to two commonly used multipurpose solutions and a saline control for 4 or 6 hours at ambient temperature. After neutralization of the disinfecting solution, track forming units were enumerated on Escherichia coli-seeded nutrient agar plates.

RESULTS

There were significant differences (P<0.01) between solutions, strains, and cysts or trophozoites, but not between the different periods. Solution 2, containing polyquaternium-1 and myristamidopropyl dimethylamine (among other ingredients), gave greater mean log reductions than did solution 1, containing polyaminopropyl biguanide and poloxamine (among other ingredients). Both solutions generally reduced more trophozoites than cysts.

CONCLUSIONS

The multipurpose solution containing polyquaternium-1 and myristamidopropyl dimethylamine reduced more cysts and trophozoites than did the alternative solution tested. Because there were differences in the effect of the multipurpose solutions on strains, it is recommended that more than one strain or species of Acanthamoeba be tested to determine efficacy of disinfecting solutions. The lack of difference between disinfection times may indicate that 4 hours could be considered as an adequate disinfecting time to ensure sufficient kill of Acanthamoeba species.

In vitro and in vivo activity of 5-fluorocytosine on Acanthamoeba

The results of our studies indicated that the avirulent Neff strain of Acanthamoeba was more susceptible to the activity of the anti-metabolite 5-fluorocytosine (5-FC) than was the virulent A-1 strain or a mouse brain reisolate of this strain, designated A-3. Results of competition experiments in which cultures were exposed simultaneously to 5-FC and either uracil, thymidine, or both uracil and thymidine demonstrated that the drug was directed against both deoxyribonucleic acid and ribonucleic acid in the avirulent strain, whereas ribonucleic acid was mainly affected in the virulent amebas. Concentrations >10 mug of 5-FC per ml were amebicidal to the avirulent strain; lower concentrations of the drug, which only affected growth slightly, significantly impaired the capacity of the cells to spontaneously encyst in stationary-phase cultures. On the other hand, the virulent strains were capable of growing in the presence of 5-FC (40 mug/ml) after an initial period of susceptibility. After a few transfers in growth medium lacking the drug, 5-FC-treated virulent amebas exhibited growth parameters typical of untreated cells. However, after successive subcultures in drug-free medium, 5-FC-treated cells lost their resistance and were again susceptible to the drug. This result suggested that the capacity of the cells to develop resistance resulted from a drug-induced mechanism. Spontaneous encystment, which was normally minimal in stationary-phase A-1 or A-3 cultures, was enhanced in A-3 but not A-1 cultures treated with 5-FC (>30 mug/ml). Results obtained from experiments to determine the effectiveness of 5-FC in protecting mice experimentally infected with either A-1 or A-3 amebas indicated that the clinical usefulness of 5-FC may be limited by the capacity of the amebas to develop resistance.

Free-living amoebae as opportunistic and non-opportunistic pathogens of humans and animals

Knowledge that free-living amoebae are capable of causing human disease dates back some 50 years, prior to which time they were regarded as harmless soil organisms or, at most, commensals of mammals. First Naegleria fowleri, then Acanthamoeba spp. and Balamuthia mandrillaris, and finally Sappinia diploidea have been recognised as etiologic agents of encephalitis; Acanthamoeba spp. are also responsible for amoebic keratitis. Some of the infections are opportunistic, occurring mainly in immunocompromised hosts (Acanthamoeba and Balamuthia encephalitides), while others are non-opportunistic (Acanthamoeba keratitis, Naegleria meningoencephalitis, and cases of Balamuthia encephalitis occurring in immunocompetent humans). The amoebae have a cosmopolitan distribution in soil and water, providing multiple opportunities for contacts with humans and animals, as evidenced by antibody titers in surveyed human populations. Although, the numbers of infections caused by these amoebae are low in comparison to other protozoal parasitoses (trypanosomiasis, toxoplasmosis, malaria, etc.), the difficulty in diagnosing them, the challenge of finding optimal antimicrobial treatments and the morbidity and relatively high mortality associated with, in particular, the encephalitides have been a cause for concern for clinical and laboratory personnel and parasitologists. This review presents information about the individual amoebae: their morphologies and life-cycles, laboratory cultivation, ecology, epidemiology, nature of the infections and appropriate antimicrobial therapies, the immune response, and molecular diagnostic procedures that have been developed for identification of the amoebae in the environment and in clinical specimens.

Decreasing effect of an anti-Nfa1 polyclonal antibody on the in vitro cytotoxicity of pathogenic Naegleria fowleri

The nfa1 gene was cloned from a cDNA library of pathogenic Naegleria fowleri by immunoscreening; it consisted of 360 bp and produced a 13.1 kDa recombinant protein (rNfa1) that showed the pseudopodia-specific localization by immunocytochemistry in the previous study. Based on the idea that the pseudopodia-specific Nfa1 protein mentioned above seems to be involved in the pathogenicity of N. fowleri, we observed the effect of an anti-Nfa1 antibody on the proliferation of N. fowleri trophozoites and the cytotoxicity of N. fowleri trophozoites on the target cells. The proliferation of N. fowleri trophozoites was inhibited after being treated with an anti-Nfa1 polyclonal antibody in a dose-dependent manner for 48 hrs. By a light microscope, CHO cells co-cultured with N. fowleri trophozoites (group I) for 48 hrs showed severe morphological destruction. On the contrary, CHO cells co-cultured with N. fowleri trophozoites and anti-Nfa1 polyclonal antibody (1:100 dilution) (group II) showed less destruction. In the LDH release assay results, group I showed 50.6% cytotoxicity, and group II showed 39.3%. Consequently, addition of an anti-Nfa1 polyclonal antibody produced a decreasing effect of in vitro cytotoxicity of N. fowleri in a dose-dependent manner.

Health effects of Acanthamoeba spp. and its potential for waterborne transmission

Risk from Acanthamoeba keratitis is complex, depending upon the virulence of the particular strain, exposure, trauma, or other stress to the eye, and host immune response. Bacterial endosymbionts may also play a factor in the pathogenicity of Acanthamoeba. Which factor(s) may be the most important is not clear. The ability of the host to produce IgA antibodies in tears may be a significant factor. The immune response of the host is a significant risk factor for GAE infection. If so, then a certain subpopulation with an inability to produce IgA in the tears may be at greatest risk. There was no sufficient data on the occurrence or types of Acanthamoeba in tapwater in the U.S. Published work on amoebal presence in tapwater does not provide information on the type of treatment the water received or the level of residual chlorine. Assessment of the pathogenicity by cell culture and molecular methods of Acanthamoeba in tapwater would also be useful in the risk assessment process for drinking water. The possibility that Acanthamoeba spp. might serve as vectors for bacterial infections from water sources also should be explored. The bacterial endosymbionts include an interesting array of pathogens such as Vibrio cholerae and Legionella pneumophila, both of which are well recognized waterborne/water-based pathogens. Work is needed to determine if control of Acanthamoeba spp. is needed to control water-based pathogens in water supplies.

Immunological characterizations of a cloned 13.1-kilodalton protein from pathogenic Naegleria fowleri

We previously cloned an antigenic gene (named nfa1) from a cDNA library of Naegleria fowleri by immunoscreening. The nfa1 gene had a coding nucleotide sequence consisting of 357 bases and produced a recombinant 13.1-kDa protein (Nfa1). In this study, to get more information regarding the recombinant Nfa1 protein (rNfa1), we produced an anti-Nfa1 polyclonal antibody from mice immunized with rNfa1 and used a peroxidase staining method to carry out immunocytochemistry experiments. In addition, we observed the effect of the presence of an anti-Nfa1 antibody on the in vitro cytotoxicity of N. fowleri against Chinese hamster ovary (CHO) cells. Trophozoites of N. fowleri in cultivation reacted strongly with a peroxidase-labeled anti-Nfa1 antibody. In inflammatory and necrotic regions of brain tissue infected with N. fowleri, labeled trophozoites that were stained brown were also observed. When examined using a transmission electron microscope, the Nfa1 protein showed pseudopodium-specific immunolocalization on a trophozoite of N. fowleri. When examined using a light microscope, CHO cells grown in cocultures with N. fowleri trophozoites (group I) for 48 h showed morphologically severe destruction but CHO cells grown in cocultures with N. fowleri trophozoites and an anti-Nfa1 polyclonal antibody (group II) showed less destruction. The results of a lactate dehydrogenase release assay showed that group I CHO cells exhibited 81% cytotoxicity and group II CHO cells exhibited 13.8% cytotoxicity.

Determination of amoebicidal activities of multipurpose contact lens solutions by using a most probable number enumeration technique

Six multipurpose contact lens solutions [All-in-One, All-in-One (Light), ReNu MultiPlus, Optifree Express, Complete, and Solo-care soft] were tested for their efficacies against Acanthamoeba castellanii trophozoites and cysts by using a most probable number (MPN) technique for amoebic enumeration. Against trophozoites, All-in-One, ReNu Multiplus, and Optifree Express achieved total kill (log reduction of >3) after the manufacturer's minimum recommended disinfection time (MMRDT), with the remaining solutions failing to reach a log reduction of 1. After 24 h of exposure, all solutions proved trophozoiticidal, achieving, with the exception of Complete (log reduction of 3.13), total kill. Against cysts, All-in-One gave a log reduction of >3 within the MMRDT, with all other solutions failing to achieve a log reduction of 1. After 24 h of exposure, All-in-One achieved total kill of cysts (log reduction of 3.74), ReNu MultiPlus gave a log reduction of 3.15, and the remaining solutions reached log reductions of between 1.09 and 2.27. The MPN technique provides a simple, reliable, and reproducible method of amoebic enumeration that depends on simply establishing the presence or absence of growth on culture plates inoculated with a series of dilutions and determining the MPN of amoebae present from statistical tables. By use of this technique, two of the multipurpose solutions tested, ReNu MultiPlus and Optifree Express, demonstrated effective trophozoiticidal activities within the recommended disinfection times; however, only All-in-One proved effective against both trophozoites and cysts over the same time period. This MPN technique, which uses axenically produced trophozoites and mature, double-walled cysts, has the potential to form the basis of a national standard for amoebicidal efficacy testing of multipurpose contact lens disinfecting solutions.

Acanthamoeba spp. as agents of disease in humans

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.

Cultivation of pathogenic and opportunistic free-living amebas

Free-living amebas are widely distributed in soil and water, particularly members of the genera Acanthamoeba and NAEGLERIA: Since the early 1960s, they have been recognized as opportunistic human pathogens, capable of causing infections of the central nervous system (CNS) in both immunocompetent and immunocompromised hosts. Naegleria is the causal agent of a fulminant CNS condition, primary amebic meningoencephalitis; Acanthamoeba is responsible for a more chronic and insidious infection of the CNS termed granulomatous amebic encephalitis, as well as amebic keratitis. Balamuthia sp. has been recognized in the past decade as another ameba implicated in CNS infections. Cultivation of these organisms in vitro provides the basis for a better understanding of the biology of these amebas, as well as an important means of isolating and identifying them from clinical samples. Naegleria and Acanthamoeba can be cultured axenically in cell-free media or on tissue culture cells as feeder layers and in cultures with bacteria as a food source. Balamuthia, which has yet to be isolated from the environment, will not grow on bacteria. Instead, it requires tissue culture cells as feeder layers or an enriched cell-free medium. The recent identification of another ameba, Sappinia diploidea, suggests that other free-living forms may also be involved as causal agents of human infections.

Molecular cloning and characterization of a gene encoding a 13.1 kDa antigenic protein of Naegleria fowleri

An antigen-related gene was cloned from a cDNA expression library of Naegleria fowleri by immunoscreening with sera obtained from mice that were either immunized with an amoebic lysate or infected with trophozoites. The coding nucleotide sequence of the cloned gene consisted of 357 bases that were translated into 119 amino acids. This gene was designated as nfa1. The predicted amino acid sequence of Nfa1 protein has two potential glycosylation and three potential phosphorylation sites, and its predicted secondary structure consists of four helices and three corners. The deduced amino acid sequence of Nfa1 protein shares 43% identity with the myohemerythrin (myoHr) protein from a marine annelid, Nereis diversicolor, including 100% identity in conserved regions and iron-binding residues. A phylogenetic tree constructed from amino acid sequences placed the N. fowleri Nfa1 protein outside of a cluster of myoHr proteins from eight invertebrates. A purified recombinant protein that migrated as a 13.1 kDa species in SDS-PAGE was produced. This recombinant protein exhibited a strong immunoreactivity with infected, immune, and anti-Nfal sera. In addition, an anti-Nfa1 serum reacted with an amoeba lysate in immunoblotting analysis. The present nfal gene encoding the myoHr-like protein is the first myoHr gene cloned from protozoa, and the Nfal antigen may be useful in diagnostic studies

Apoptosis of primary-culture rat microglial cells induced by pathogenic Acanthamoeba spp

To determine whether trophozoites and lysates of pathogenic Acanthamoeba spp. induce apoptosis in primary-culture microglial cells, transmission electron microscopic (TEM) examinations, assessment of DNA fragmentation by agarose gel electrophoresis, and the TdT-mediated dUTP nick-end labeling assay were performed. When a trophozoite of pathogenic Acanthamoeba culbertsoni came in contact with a microglial cell, the digipodium was observed by TEM. Nuclear chromatin condensation was observed in 10% of microglial cells, while it was not revealed when they were cocultured with weakly pathogenic Acanthamoeba royreba trophozoites. DNA fragmentation in microglial cells cocultured with the A. culbertsoni lysate was detected by electrophoresis, showing DNA ladder formation, whereas it was hardly observed in microglial cells cocultured with A. royreba. DNA fragmentation of microglial cells was also confirmed by flow cytometry analysis. The fluorescence of TdT-stained apoptotic bodies became intensely visible with microglial cells cocultured with the A. culbertsoni lysate. In contrast, with microglial cells cocultured with the A. royreba lysate, only a background level of fluorescence of TdT-stained apoptotic bodies was detected. These results suggest that some rat microglial cells cocultured with pathogenic A. culbertsoni undergo cytopathic changes which show the characteristics of the apoptotic process, such as nuclear condensation and DNA fragmentation.

Proteinase activities in total extracts and in medium conditioned by Acanthamoeba polyphaga trophozoites

Acanthamoeba species can cause granulomatous encephalitis and keratitis in man. The mechanisms that underlie tissue damage and invasion by the amoebae are poorly understood, but involvement of as yet uncharacterized proteinases has been suggested. Here, we employed gelatin-containing gels and azocasein assays to examine proteinase activities in cell lysates and in medium conditioned by Acanthamoeba polyphaga trophozoites. Azocasein hydrolysis by cell lysates was optimally detected at pH 4.0-5.0 and was predominantly associated with the activity of cysteine proteinases. Compatible with enzyme activation during secretion, culture supernatants additionally contained a prominent azocasein hydrolyzing activity attributable to serine proteinases; these enzymes were better detected at pH 6.0 and above, and resolved at 47, 60, 75, 100, and >110 kDa in overlay gelatin gels. Although a similar banding profile was observed in gels of trophozoite lysates, intracellular serine proteinases were shown to be activated during electrophoresis and to split the substrate during migration in sodium dodecyl sulfate gels. Blockage of serine proteinases with phenylmethylsulfonylfluoride prior to electrophoresis permitted the detection of 43-, 59-, 70-, and 100-130-kDa acidic cysteine proteinases in cell lysates, and of 3 (43, 70, and 130 kDa) apparently equivalent enzymes in culture supernatants. Under the conditions employed, no band associated with a metalloproteinase activity could be depicted in substrate gels, although the discrete inhibition of supernatants' azocaseinolytic activity by 1,10-phenanthroline suggested secretion of some metalloproteinase.

Acanthamoeba keratitis

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. The first cases were recognized in 1973, but the disease remained very rare until the 1980s, when an increase in incidence mainly associated with contact lens wear was reported. There is an increased risk when contact lens rinsing and soaking solutions are prepared with nonsterile water and salt tablets. The clinical picture is often characterized by severe pain with an early superficial keratitis that is often treated as herpes simplex infection. Subsequently a characteristic radial perineural infiltration may be seen, and ring infiltration is common. Limbitis and scleritis are frequent. Laboratory diagnosis is primarily by culture of epithelial samples inoculated onto agar plates spread with bacteria. Direct microscopy of samples using stains for the cyst wall or immunostaining may also be employed. A variety of topically applied therapeutic agents are thought to be effective, including propamidine isethionate, clotrimazole, polyhexamethylene biguanide, and chlorhexidine. Various combinations of these and other agents have been employed, often resulting in medical cure, especially if treatment is commenced early in the course of the disease. Penetrating keratoplasty is preferably avoided in inflamed eyes, but may be necessary in severe cases to preserve the globe or, when the infection has resolved, to restore corneal clarity for optical reasons.

Modulation of complement resistance and virulence of Naegleria fowleri amoebae by alterations in growth media

Highly-pathogenic, mouse-passaged Naegleria fowleri amoebae are complement resistant. The present study evaluates the effect of complement on N. fowleri and the virulence of the amoebae after animal passage and growth in two different axenic media. Pathogenic N. fowleri maintained in "enriched" Cline medium are virulent for mice and resistant to complement lysis. A rapid decline in resistance to complement and virulence for mice is observed when highly-pathogenic N. fowleri are grown in Nelson medium lacking hemin. N. fowleri maintained in Nelson medium can be rendered complement-resistant by shifting the amoebae to growth in Cline medium for 2 h prior to the addition of complement. Cycloheximide treatment of N. fowleri maintained in Nelson medium blocks the transition to a complement-resistant phenotype following a shift in growth medium. Proteins were radiolabeled with [35S] during a shift from Nelson to Cline medium to identify specific polypeptides which may be associated with the functional activities related to virulence and resistance to complement.

Balamuthia mandrillaris, N. G., N. Sp., agent of amebic meningoencephalitis in humans and other animals

We recently reported the isolation of a leptomyxid ameba from the brain of a mandrill baboon that died of meningoencephalitis. Based on light and electron microscopic studies, animal pathogenicity tests, and immunofluorescence patterns, we conclude that our isolate differs fundamentally from the other two amebas (Leptomyxa and Gephyramoeba) included in the Order Leptomyxida. We therefore created a new genus, Balamuthia, to accommodate our isolate and described it as Balamuthia mandrillaris to reflect the origin of the type species. Briefly, B. mandrillaris is a pathogenic ameba that causes amebic encephalitis in humans and animals. It has trophic and cyst stages in its life cycle, and is uninucleate with a large vesicular nucleus and a central nucleolus. Mature cysts have a tripartite wall consisting of an outer loose ectocyst, an inner endocyst and a middle mesocyst. Unlike Acanthamoeba and Naegleria, the other two amebas that cause amebic encephalitis in humans, Balamuthia will not grow on agar plates seeded with enteric bacteria. However, Balamuthia grows on a variety of mammalian cell cultures and kills mice following intranasal or intraperitoneal inoculation. Based on immunofluorescence testing, 35 cases of amebic encephalitis in humans and three in other animals have been identified worldwide as being caused by Balamuthia.

Isolation of Acanthamoeba sp. from a greyhound with pneumonia and granulomatous amebic encephalitis

Acanthamoeba were isolated from a naturally occurring animal infection of granulomatous amebic encephalitis. The amebas were grown from lung lesions from a 1-year-old greyhound puppy, which was 1 of several dogs in a kennel that was affected by a progressive fatal neurologic and respiratory disease. The Centers for Disease Control, Atlanta, Georgia, confirmed the disease to be acanthamebiasis and specifically identified the amebas as Acanthamoeba culbertsoni by fluorescent antibody testing on brain tissue from the dog. The amebas were cultured initially on potato dextrose agar and on nonnutrient agar plates that were seeded with a lawn of nonpathogenic Escherichia coli. The isolate was then transferred to nonnutrient agar plates containing killed Enterobacter aerogenes and subsequently to axenic medium and cell cultures. The isolate was highly pathogenic by intranasal inoculation into 2-week-old mice.

In vitro susceptibility of Acanthamoeba culbertsoni to inhibitors of folate biosynthesis

The effects of different sulphonamides, dihydrofolate reductase inhibitors and other inhibitors of folate metabolism on growth of Acanthamoeba culbertsoni in a chemically defined medium are reported. Among the sulphonamides, sulphamethoxazole and sulphadiazine were most effective followed by sulphanilamide and sulphaguanidine. Inhibition by each sulphonamide was reversed by p-aminobenzoic acid as well as folic acid. 7-Methylguanosine, a pteridine synthesis-inhibitor, did not inhibit multiplication of A. culbertsoni. Among the dihydrofolate reductase inhibitors, pyrimethamine blocked the amoebic growth at 100 micrograms/ml, while trimethoprim and cycloguanil palmoate failed to cause significant inhibition of growth even at 250 micrograms/ml. Metoprine inhibited amoebic growth completely at 50 micrograms/ml. Methotrexate and a thymidylate synthetase inhibitor 5-fluorouracil inhibited growth strongly, with IC50 values (the concentration of the drug which causes 50% inhibition of the growth at 72 h) of 1.97 and 2.45 micrograms/ml, respectively. Inhibition by methotrexate, metoprine or 5-fluorouracil could not be reversed by folic acid, folinic acid, thymidine, or folinic acid plus thymidine. The results indicate unusual features in A. culbertsoni folate metabolism.

[Immunological approach for classification of free-living amoeba in Korea]

Acanthamoeba spp., free-living amoebae inhabited in moist soil, pond, freshwater, sewage, atmosphere and swimming pool, may be causative protozoa of the fatal primary amoebic meningoencephalitis in experimental animals and humans. In this study, Acanthamoeba spp., including Acanthamoeba sp. YM-4 (isolated strain from Korea) had been compared by the two-dimensional electrophoresis and hybridoma technique as well as the difference of morphological characteristics. Trophozoite of Acanthamoeba sp. YM-4 is usually uninucleate and show the hyaline filamentous projections (acanthopoda). No flagellate stage observed. Cysts have two walls, the outer wall is nearly circular, but inner wall is oval or some irregular. As results of SDS-PAGE for lysate of Acanthamoeba sp. YM-4, 16 major protein fractions are similar to those of A. culbertsoni, but different to A. royreba and A. polyphaga. Findings of two-dimensional electrophoretic patterns of Acanthamoeba sp. YM-4 are almost same to those of A. culbertsoni, The isotype of monoclonal antibodies produced from McAY 6, McAY 7, McAY 8, McAY 13 and McAY 16 clones were IgG1, and McAY 10 and McAY 11 clones were IgM. As results of the cross-reactivity among various amoebae using ELISA with monoclonal antibodies, McAY 7 monoclonal antibody (molecular weight 43 kDa by EITB) was only reacted with Acanthamoeba sp. YM-4, but McAY 6 and McAY 10 monoclonal antibodies were reacted to A. culbertsoni as well as Acanthamoeba sp. YM-4.

Alterations in protein expression and complement resistance of pathogenic Naegleria amoebae

Highly pathogenic strains of Naegleria fowleri activate the alternative complement pathway but are resistant to lysis. In contrast, weakly pathogenic and nonpathogenic Naegleria spp. activate the complement pathway and are readily lysed. The present study was undertaken to determine whether surface components on amoebae accounted for resistance to complement lysis. Enzymatic removal of surface components from highly pathogenic N. fowleri with phosphatidylinositol-specific phospholipase C or with endoglycosidase H increased the susceptibility of these amoebae to complement-mediated lysis. Similar treatment of nonpathogenic amoebae had no effect on susceptibility to complement. Tunicamycin treatment of highly and weakly pathogenic N. fowleri increased susceptibility to lysis by complement in a dose-related manner. Tunicamycin treatment did not alter the susceptibility of nonpathogenic amoebae to complement. Proteins of 234 and 47 kDa were detected in supernatant fluid from phosphatidylinositol-specific phospholipase C-treated highly pathogenic amoebae but not in supernatant fluid from phosphatidylinositol-specific phospholipase C-treated weakly pathogenic amoebae. Electrophoretic analysis of iodinated surface proteins of highly pathogenic N. fowleri revealed species of 89, 60, 44, and 28 kDa. Western immunoblots of lysates from surface-iodinated amoebae were stained with biotinylated concanavalin A or biotinylated Ulex europaeus agglutinin I. Surface proteins, identified in highly pathogenic amoebae by iodination, were shown to be glycoproteins by lectin analysis specific for the detection of mannose and fucose residues.

[The protective effects of monoclonal antibodies in mice from Naegleria fowleri infection]

Protective effects of monoclonal antibodies against N. fowleri were comparatively studied. BALB/c mice were treated with two types of monoclonal antibodies, Nf 2 and Nf 154, before and after the infection with N. fowleri. The mortality and mean survival times were then compared. Also, direct effect of the monoclonal antibodies on the N. fowleri trophozoites in vitro were observed. In vitro protective effects of the monoclonal antibodies were also studied in cells infected with N. fowleri. The observed results are summarized as follows: 1. Among mice pretreated twice before the infection with monoclonal antibody Nf 2(McAb Nf 2), only 15.8% were killed, and the mean survival time was 17.7 days. This was not much different from the mice pretreated once, as the mortality and mean survival time were 16.7% and 17 days. Those effects were compatible with monoclonal antibody Nf 154(McAb Nf 154). The above findings contrast with the mortality and mean survival time of the control mice, which were 22.7% and 14.6 days respectively. 2. Mice which received twice the McAb Nf 2 following N. fowleri infection incurred a 19.4% mortality rate with 13.6 days survival time; 17.9% and 15.8 days with on time administration, in contrast to the 25% and 14.6 days in the control group. 3. Marked agglutination effect of McAb Nf 2 or McAb Nf 154 were observed on N. fowleri trophozoites. 4. When N. fowleri trophozoites were treated with McAb Nf 2 or McAb Nf 154 combined with comments, the proliferation rate was more significantly suppressed than in that the control. 5. N. fowleri trophozoites treated with McAb Nf 2 or McAb Nf 154 showed an increased number of swollen mitochondria, disfigured cisternae, lipid droplets, and osmiophilic granules in the cytoplasm. 6. A remarkable protective effect of monoclonal antibodies was noticed in CHO cells infected with N. fowleri. More than 90.6% of the infected CHO cells survived, contrasted with 27% of untreated cells. The overall results in this study suggest that N. fowleri treated with monoclonal antibodies against N. fowleri reduce the mortality and prolong the survival time of the mice when the antibodies are administered before the infection. The protective effect of the monoclonal antibodies is surmised being caused by agglutination of the trophozoites.

Free-living amoebae: pathogenicity and immunity

Free-living amoebae causes three well-defined disease entities: (i) primary amoebic meningoencephalitis, caused by Naegleria fowleri, (ii) granulomatous amoebic encephalitis and (iii) chronic amoebic keratitis, caused by species of Acanthamoeba. Both Naegleria infections and chronic amoebic keratitis occur in healthy individuals while granulomatous amoebic encephalitis is often associated with patients with acquired immunodeficiencies. The different pathogenic behaviour of these organisms is associated with differences in life cycle, amoeboidal locomotion, enzyme composition (such as phospholipase A), and cytotoxins, as well as natural host immunity. Immunity against these amoebae (whether acquired or natural) involves a combination of complement, antibody and cell-mediated immunity. Evidence suggests that the major mechanisms of immunity against these amoebae is activation of phagocytic cells, especially neutrophils, by lymphokines and opsonization of the amoebae by antibody which promote an antibody dependent cellular destruction of the organism.

Epidemiology of free-living ameba infections

Small free-living amebas belonging to the genera Acanthamoeba and Naegleria occur world-wide. They have been isolated from a variety of habitats including fresh water, thermal discharges of power plants, soil, sewage and also from the nose and throats of patients with respiratory illness as well as healthy persons. Although the true incidence of human infections with these amebas is not known, it is believed that as many as 200 cases of central nervous system infections due to these amebas have occurred worldwide. A majority (144) of these cases have been due to Naegleria fowleri which causes an acute, fulminating disease, primary amebic meningoencephalitis. The remaining 56 cases have been reported as due either to Acanthamoeba or some other free-living ameba which causes a subacute and/or chronic infection called granulomatous amebic encephalitis (GAE). Acanthamoeba, in addition to causing GAE, also causes nonfatal, but nevertheless painful, vision-threatening infections of the human cornea, Acanthamoeba keratitis. Infections due to Acanthamoeba have also been reported in a variety of animals. These observations, together with the fact that Acanthamoeba spp., Naegleria fowleri, and Hartmannella sp. can harbor pathogenic microorganisms such as Legionella and or mycobacteria indicate the public health importance of these amebas.

Nutritional studies on Acanthamoeba culbertsoni and development of chemically defined medium

A chemically defined medium containing 11 amino acids, 3 vitamins, 6 inorganic salts and glucose, yielding maximum cell densities of 1.5-2.5 x 10(7) cells/ml, has been developed for Acanthamoeba culbertsoni with a mean generation time (MGT) of 10 h. A medium containing six amino acids viz. arginine, methionine, leucine, isoleucine, valine and glycine along with other components could also support good albeit slower growth (MGT 27 h) of the amoeba. Acetate did not serve as a suitable carbon/energy source for A. culbertsoni. This organism bears close resemblance in its nutritional requirements to other Acanthamoeba especially A. polyphaga.

[Studies on the cell-mediated immunity in experimental Naegleria spp. infections]

Observations were made on the differences in cell-mediated immune responses in the mice infected with strongly pathogenic Naegleria fowleri ITMAP 359, weakly pathogenic Naegleria jadini 0400, or non-pathogenic Naegleria gruberi EGB, respectively. Variations in cell-mediated responses and changes in antibody titers according to the duration after infection were noted. Infections were done by dropping 5 microliters saline suspension containing 10 x 10(4) trophozoites cultured axenically in the CGVS medium into the right nasal cavity of ICR mice aging about 6-7 weeks, under the anesthesia by intraperitoneal injection of secobarbital. Following infection, delayed type hypersensitivity(DTH) responses in the footpad and blastogenic responses of the mouse spleen cells using [3H]-thymidine were observed on the day 1, 4, 7, 10 and 14 after infection. For the preparation of amoeba lysates, each of cultured trophozoites were homogenized with an ultrasonicator, and centrifugated at 20,000 g. The supernatants of amoeba lysates were used as the mitogen and antigen for ELISA. Concanavalin A(Con. A) and lipopolysaccharide(LPS) were also used as mitogens in the blastogenic response. 1. The mice infected with N. fowleri showed the mortality rate of 75.7%. The rate was 6.2% for the N. jadini infected group, while no dead mouse was observed for N. gruberi infections. 2. In regard to DTH responses in the N. fowleri infected mice, the level increased in comparison to the control group but declined after 7 days. An increase was also noted for the N. jadini group after 1 day, but gradual decreases were observed through the infection period. In addition, no difference was noted between the N. gruberi infected and control groups. 3. Concerning the blastogenic response of the splenocytes, it increased after 10 days in the experimental group of N. fowleri infection, but the differences were not statistically significant compared with control group. It was evident that N. jadini group was not different from control group either, while there was a tendency of decrease in N. gruberi infected group. In regard to the blastogenic response of the splenocytes by LPS, it was found that the N. fowleri, N. jadini and N. gruberi infected groups had no differences from the control group. 4. The serum antibody titer of N. fowleri and N. jadini infected mice increased from the day 7 and 14 after infection respectively, while the N. gruberi infected mice showed no increase.(ABSTRACT TRUNCATED AT 400 WORDS)

Biology of Naegleria spp

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