Response to Tan and Stenzel, and Windsor et al.: Blastocystis reproduction and morphology

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Response to Tan and Stenzel, and Windsor et al.: Blastocystis reproduction and morphology
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  goodsupportingevidence,theymustcontinuetoremainashypotheses. The current and only accepted mode of reproduction for  Blastocystis  is binary fission. The poly-morphic nature of this protozoan parasite can misleadresearchers into seeing things that are not necessarilythere, and so caution is warranted when studying  Blastocystis  cell biology. References 1 Govind, S.K.  et al.  (2002) Multiple reproductive processes in  Blasto-cystis .  Trends Parasitol.  18, 5282 Stenzel,D.J.andBoreham, P.F.L.(1996)  Blastocystishominis revisited. Clin. Microbiol. Rev.  9, 563–5843 Tan,K.S.  etal. (2002)Recentadvancesin  Blastocystishominis research:hot spots in  terra incognita .  Int. J. Parasitol.  32, 789–8044 Suresh, K.  et al.  (1994) A multiple fission-like mode of asexualreproduction in  Blastocystis hominis .  Parasitol. Res.  80, 523–5275 Suresh, K.  et al.  (1997) Sac-like pouches in  Blastocystis  from the houselizard  Cosymbotus platyurus .  Parasitol. Res.  83, 523–525 1471-4922/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S1471-4922(03)00119-3 | Letters Response Response to Tan and Stenzel, and Windsor  et al. : Blastocystis   reproduction and morphology Suresh Kumar Govind 1 , Khairul A. Anuar 1 and Huw V. Smith 2 1 Department of Parasitology, Faculty of Medicine, University of Malaya, 50603, Kuala Lumpur, Malaysia 2 Scottish Parasite Diagnostic Laboratory, Stophill Hospital, Glasgow, G21 3UW, UK We agree with the comments from Tan and Stenzel, andWindsor  et al.  regarding our letter [1] in that the diversemorphologiesexhibitedby  Blastocystis hasgeneratedbothcuriosity and limited progress into its biology anddescription of its life cycle. Similarly, we agree that theuse of techniques that provide only morphological insightcanbeinsufficientfordeterminingreproductiveprocesses,and concur that assessments based on limited informationhas led to confusion.Our observations demonstrated that budding in  Blas-tocystis  occurred concurrently with binary fission incultures exposed to nutritional or drug stress, and thatthe budded forms developed into vacuolar forms in bothstressed and fresh cultures [2]. Sac-like pouches appearedin cells with prominent mitochondria, a feature that wasassociated, ultrastructurally, with the transformationfrom vacuolar to cystic forms [3]. In these studies,organism viability (assessed using vital dyes) was often . 98%. In addition, we did not suggest an association of flagella-like structures with  Blastocystis  in the micro-graph referred to by Tan and Stenzel [4], however, this is asubjective interpretation based on one image.It should be emphasized that our interpretations arenot based on light and electron microscopy studies alone.Support for the presence of grape-like clusters within the  Blastocystis  ‘host cell’ originally came from scanningelectron micrographs [5]. Further evidence was based onthe incorporation of acridine orange into these grape-likeclusters, which highlighted many bright yellow-greenstaining foci (suggestive of DNA binding) in the centralbody forms within an individual mother cell [5]. Morerecently, we used both fluorogenic (Hoechst 33342 andDAPI) and tinctorial (Trichrome) stains to provideadditional evidence that the smaller central bodies withinthe host cell contained nucleic acids [6], supporting the possibility that these grape-like clusters are progeny. Wealso agree that it is important to demonstrate that theseprogeny develop into viable adult cells. Our observationsindicate that individuals from the grape-like clusterstransferred into fresh cultures produce recognized mor-phological progeny. However, exhaustive, selectivedepletion of the larger, morphological forms is necessarybefore this hypothesis can be substantiated.We were aware of the suggestion that central vacuoleformation was a feature of irreversible cellular degener-ation. But, we do not find it incompatible with thisphenomenon being a precursor to progeny release becausethe photomicrographs in Suresh  et al.  [3,5] providedevidence that these forms could be released followingrupture and/or degradation of the cell.Wedisagreewiththecommentthatlightmicroscopy(orits derivatives) lacks the capability to provide valuableinsights into  Blastocystis  cell biology. Indeed, imagesderived from  in situ  localization of organelles and thedemonstration of bioactive systems in viable organisms,using fluorescent and other reporters, have providedsignificant insights into protozoan organization andbiology. Such insights are also more likely to occur wheninformation from both microscopic and ultrastructuralapproaches is integrated.The constraints of extrapolating information from in vitro  studies of   Blastocystis  and other organisms arerecognized, but much of our current understanding on  Blastocystis  biology is obtained from these studies.Standardization of methods and quality assurance willdrive a clearer understanding of the significance of   Blastocystis  polymorphism.  Blastocystis  exists in diversemorphological forms, including the infrequently reportedavacuolar form, and the multivacuolar form seen in fresh Corresponding author:  Huw V. Smith (h.v.smith@spdl.org.uk). Update  TRENDS in Parasitology   Vol.19 No.7 July 2003 291 http://trepar.trends.com  faeces,butthereasonbehindthesediversemorphologiesisnot clear. Are they manifestations of inadequate adap-tation to culture  in vitro  or are they programmedconsequences of infection? The large increase in parasitenumbers seen within a short period of time  in vitro  isdifficult to reconcile if binary fission is the only mode of reproduction. The information presented in our letter andthe responses highlight the need for more research into  Blastocystis  cell biology, using a variety of diverse, butcomplementary, approaches. This is a suitable time forsuch action, given the range of molecular and  in situ biochemical, biophysical andultrastructural methodsnowavailable. References 1 Govind, S.K.  et al.  (2002) Multiple reproductive processes in  Blas-tocystis .  Trends Parasitol.  18, 5282 Suresh, K.  et al.  (1998) Budding in  Blastocystis .  Int. Med. Res. J.  2,13–143 Suresh, K.  et al.  (1993) Ultrastructural changes during  in vitro encystment of   Blastocystis hominis .  Parasitol. Res.  80, 327–3354 Suresh, K.  et al.  (1997) Sac-like pouches in  Blastocystis  from the houselizard  Cosymbotus platyurus .  Parasitol. Res.  83, 523–5255 Suresh, K.  et al.  (1994) A multiple fission-like mode of asexualreproduction in  Blastocystis hominis .  Parasitol. Res.  80, 523–5276 Suresh, K.  et al.  (2001) Are nucleic acids of   Blastocystis  extruded intothe central body?  Trans. R. Soc. Trop. Med. Hyg.  94, 618 1471-4922/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S1471-4922(03)00140-5 | Erratum Corrigendum to: Molecular parasitology of malaria inPapua New Guinea [Trends in Parasitology 19 (2003) 246–249]  In the June issue of   Trends in Parasitology  on http://www.parasites.trends.com, there was an omission in the article:MolecularparasitologyofmalariainPapuaNewGuineaby Alfred Corte´s  et al. Theauthorswanttoincludeareferenceinthefollowingsentence: With these surveys, it is intended to establish agenotype resistance index, as suggested by Djimde´  et al. [46], that will be determined by the prevalence of pointmutations in drug-resistance marker genes within thecirculating parasite population together with observedclinical treatment failures in the same communities(B. Genton, pers. commun.).46 Djimde´, A.  et al.  (2001) Application of a molecularmarker for surveillance of chloroquine-resistant falci-parum malaria.  Lancet  358, 890–891The authors wish to apologize for this omission. 1471-4922/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S1471-4922(03)00142-9 Do you want to reproduce material from a  Trends   journal? This publication and the individual contributions within it are protected by the copyright of Elsevier Science. Except as outlined inthe terms and conditions (see p. ii), no part of any  Trends   journal can be reproduced, either in print or electronic form, withoutwritten permission from Elsevier Science. Please address any permission requests to:Rights and Permissions,Elsevier Science Ltd,PO Box 800, Oxford, UK OX5 1DX. Update  TRENDS in Parasitology   Vol.19 No.7 July 2003292 http://trepar.trends.com
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