The morphology, formation and development of cysts of<i>Entamoeba</i>

McConnachie, Elspeth W.

doi:10.1017/s003118200006981x

Cited by 53 publications

(26 citation statements)

References 44 publications

(63 reference statements)

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“…The engulfment of bacteria by B. hominis has been reported (Dunn et al 1989). It has also been suggested that the amoeboid form is an intermediate form between the vacuolar and cyst forms and that it ingests bacteria to provide nutrition for the encystation (Singh et al 1995), as has previously been shown for Entamoeba (McConnachie 1969). Isolates of B. hominis may differ in their ability to produce the amoeboid form, which could be a factor contributing to pathogenicity.…”

Section: Discussionmentioning

confidence: 90%

Predominance of amoeboid forms of Blastocystis hominis in isolates from symptomatic patients

Tan

2005

Parasitol Res

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Blastocystis hominis is one of the most common human parasites that inhabit the intestinal tract. Conflicting reports continue to exist regarding the existence and the functional role of the amoeboid forms in the life cycle of the parasite. The present study investigates the presence of these forms in 20 isolates obtained from ten symptomatic and asymptomatic patients respectively. A total of 10,000 parasite cells per ml from each isolate were inoculated into three culture tubes each containing 3 ml of Jones' medium supplemented with 10% horse serum, incubated at 37 degrees C. The contents were examined daily for 10 days. Irregular and polymorphic amoeboid forms with multiple extended pseudopodia were observed in all isolates from symptomatic patients, while none of the isolates from asymptomatic patients showed the presence of the amoeboid forms. The amoeboid forms were initially noted on day 2 and the percentages increased from 2% to 28%, with peak percentages from day 3 to day 6. Transmission electron microscopy revealed two types of amoeboid forms; one containing a large central vacuole completely filled with tiny electron-dense granules, and the other which revealed multiple small vacuoles within the central body. The cytoplasm contained strands of electron-dense granules resembling rough endoplasmatic reticulum, which is suggestive of active protein synthesis. The surface coat of the amoeboid form surrounding the parasite showed uneven thickness. Acridine orange stained the central body yellow and the periphery orange, indicating activity at the level of nucleic acids. The amoeboid form could either be an indicator of pathogenicity of B. hominis, or the form likely to contribute to pathogenicity and be responsible for the symptoms seen in patients.

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Section: Discussionmentioning

confidence: 90%

Predominance of amoeboid forms of Blastocystis hominis in isolates from symptomatic patients

Tan

2005

Parasitol Res

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“…The amoeboid form allows the parasite to engulf bacteria, which are needed for nutritive purposes to enhance the process of encystation, as has also been seen in Entamoeba (McConnachie 1969).…”

Section: Discussionmentioning

confidence: 99%

Ultrastructural changes during in vitro encystment ofBlastocystis hominis

et al. 1994

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The morphological changes occurring in Blastocystis hominis at different time points following in vitro encystment were studied by electron microscopy. The following stages of the parasite were sequentially seen: (a) the amoebic form, which was irregular in shape, with a majority of the organelles being concentrated at the condensed cytoplasmic region; (b) the pre-cystic form, which was rounded and had an electron-dense material forming a homogeneous wall around the central body; and (c) the cystic form, which had a very prominent, thick osmiophilic electron-dense wall, within which there were many inclusions and possibly reproductive granules. The amoebic form appeared to be an intermediate stage between the vacuolar form and the pre-cystic form, as this stage allowed the parasite to ingest bacteria to enhance encystment. The pre-cystic stage had previously been shown in experimental infection to be infective. The role of the cystic stage in producing infection is currently being investigated.

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“…Although they have been described previously for Entamoeba histolytica (Dobell 1928;Cleveland and Sanders 1930), little is known about the mechanisms involved. Since E. histolytica cannot be induced to encyst in axenic culture, studies have been conducted on axenic in vitro encystation of Entamoeba invadens, a reptile parasite, as a useful model for encystation of E. histolytica (Lo´pez-Romero and Villago´mez-Castro 1993), because of its close similarity with E. histolytica in morphology and life cycle (McConnachie 1969). Since the excystation and metacystic development of E. histolytica (Dobell 1928;Cleveland and Sanders 1930) and of E. invadens (Geiman and Ratcliffe 1936) look similar, in vitro excystation of E. invadens may also become a useful model for excystation of the human parasite.…”

Section: Introductionmentioning

confidence: 99%

Possible role of calcium ions, calcium channels and calmodulin in excystation and metacystic development of Entamoeba invadens

Makioka

Kumagai

Kobayashi

et al. 2002

Parasitology Research

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The effect of calcium ions (Ca(2+)) and calmodulin (CaM) on the excystation and metacystic development of Entamoeba invadens was examined by transfer of cysts to a growth medium containing calcium antagonists and CaM inhibitors. Excystation, which was assessed by counting the number of metacystic amoebae after induction of excystation, was inhibited by the calcium chelators ethyleneglycol bis (beta-aminoethyl ether)- N,N'-tetraacetate (EGTA) and ethylene-diaminetetraacetate (EDTA), with EDTA being more potent than EGTA. The inhibitory effect of higher concentrations of these chelators on excystation was associated with reduced viability of cysts. Metacystic development, when determined by the number of nuclei in an amoeba, was delayed by EGTA, because the percentage of four-nucleate amoebae was higher than in controls at day 3 of incubation. EDTA made metacystic development unusual by producing a large number of metacystic amoebae with more than ten nuclei. The inhibition of excystation by these chelators was partially abrogated by their removal. A putative antagonist of intracellular calcium flux, 8-( N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate (TMB-8) also inhibited the excystation and metacystic development, but had little effect on cyst viability. The slow Na(+)-Ca(2+) channel blocker bepridil but not verapamil inhibited the excystation and metacystic development, associating with reduced cyst viability at higher concentrations. The inhibitory effect of bepridil on excystation was abrogated by removal of the drug. The CaM inhibitor trifIuoperazine (TFP) but not W-7 [ N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide] inhibited the excystation and metacystic development. The inhibitory effect of TFP on excystation was also abrogated by removal of the drug. These results indicate that extracellular calcium ions, amoebic intracellular calcium flux, calcium channels, and a CaM-dependent process contribute to the excystation and metacystic development of E. invadens.

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The morphology, formation and development of cysts ofEntamoeba

Cited by 53 publications

References 44 publications

Predominance of amoeboid forms of Blastocystis hominis in isolates from symptomatic patients

Predominance of amoeboid forms of Blastocystis hominis in isolates from symptomatic patients

Ultrastructural changes during in vitro encystment ofBlastocystis hominis

Possible role of calcium ions, calcium channels and calmodulin in excystation and metacystic development of Entamoeba invadens

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