Tuesday, December 18, 2012

Blastocystis Highlights 2012

2012 is coming to an end and it is also time for taking stock of the year Blastocystis-wise. We saw many significant scientific papers, among them a paper by Poirier and colleagues, predicting a potential role for Blastocystis in irritable bowel syndrome (IBS), based on analysis of their recent genome data.They propose that Blastocystis is genetically armed with the equipment necessary to cause intestinal dysbiosis, and potentially IBS, which may be a cause of dysbiosis. Indeed, members of this group found that the Blastocystis genome encodes various proteases and hydrolases that, if secreted, may be involved with perturbations of the gut flora; however, we need transcriptional profiling or similar studies to find out, whether these enzymes are actually expressed. Some species of Entamoeba are also in possession of multiple "virulence genes", but for some species they apparently remain un-expressed, and most Entamoeba species are still considered harmless.

Tsaousis et al. (2012) studied the so-called “iron/sulfur (Fe/S) cluster biosynthetic machinery”, which is a key component in bacteria and eukaryotes and necessary for various essential cell functions, among them electron transport, enzymatic catalyses and regulation of gene expression. Their study is one of the relatively few studies that seek to obtain a better understanding of the biochemical and organellar structure and function of Blastocystis, which will eventually help us understand this “in-between” organism: Blastocystis belongs to Stramenopiles and is unique in many ways, in part since it is the only intestinal parasite of man that belongs to this group of organisms, in part since it is very different from most other species belonging to this group, especially due to its anaerobic adaptation. Indeed, this paper is a link to a better understanding of how Blastocystis has so successfully adapted to its life in (and outside?) the human intestine. The authors show that Blastocystis is in possession of genes associated with the synthesis of Fe/S cluster that may have been acquired by an ancestor of Blastocystis by lateral gene transfer from a methanoarchaeon; some methanoarchaea are common inhabitants of the human intestinal tract and producers of methane.

Indirect immunofluorescence of the gut archaeon Methanobrevibacter smithii
with specific calibrated antibody probe. Source.
This year also saw papers contributing to the debate on how to treat Blastocystis. Among them a paper by Hellemond et al. (2012) based on a retrospective study of patients for whom treatment regimen was known (Paromomycin (3 daily doses of 500 mg for 7-10 days), Clioquinol (3 daily doses of 250 mg for 7 days) or Metronidazole (3 daily doses of 500 mg for 7-10 days)) and for whom post-treatment stool samples had been available for analysis. They found that the spontaneous resolution of Blastocystis was low and that among the three drugs, paromomycin was superior with an eradication rate of 77%. Clioquinol and metronidazole both had an eradication rate of 38%, while lack of intervention (no treatment) had an eradication rate of 22%, suggesting that drug intake has some effect in eradicating Blastocystis.

Eukaryotic microbiota, including Blastocystis, was studied by cloning of 18S PCR products by Pandey et al. (2012) and Hamad et al. (2012). Interestingly, the eukarytoic microbiota is still approached only by "old-fashioned" cloning and Sanger sequencing and not by next gen seqeuncing methods or even newer methods. While the results of the studies are hardly surprising, Pandey draws an important parallel to micro-eukaryotes of ruminants. Here, micro-eukaryotes, mainly ciliates possibly, contribute significantly to storing starch; “the uptake of starch and sugars is known to have a stabilizing effect in ruminants fed high-grain diets (…) protozoa were shown to play an integral role in digestion in ruminants, and thus would definitely have a role to play in the case of humans. One of the important roles could be to control bacterial numbers by predation or inhibition in the human gut.” Pandey mentions Blastocystis , which was common among the sequenced clones. The authors speculate that Blastocystis might predate on beneficial bacteria. Meanwhile, I do not think that we have evidence for bacterial phagocytosis in Blastocystis yet, but I may be wrong.

There was a fine paper in Trends in Parasitology by Pauline Scanlan, highlighting some of the pitfalls in Blastocystis research. Scanlan calls for further standardisation in epidemiological studies seeking to test for associations between Blastocystis colonisation intensity ("parasite burden") and/or genetic diversity and symptoms. Incidentally, Scanlan also co-authored an interesting paper back in 2008 on micro-eukaryotic diversity of the human distal gut microbiota, thus heralding the works by Hamad and Pandey, and what we are going to see a lot more of in 2013 and the years ahead, namely culture-independent, high-throughput identification of eukaryotic signatures in faecal samples.

It is great to see more and more research engaging in subtyping to expand on host specificity and to look for epidemiological associations between subtypes and health/disease phenotypes.It appears that there are no unequivocal trends in most of the populations studied so far when it comes to analysis of simple associations. However, two different methods are used for subtyping, and data obtained by one of the methods should be interpreted with some care (see below).

It was also interesting to see a paper from Lima, Peru, reporting on a 40% Blastocystis prevalence in an Amazonic community of Peru (and 29% Giardia!) using a simple sedimentation technique (Machicado et al., 2012). Children in day care centres in Cuba were also climbing towards a positive rate of 40% using a combo of conventional methods (Canete et al., 2012), and it is evident, that the use of PCR would significantly increase these figures, suggesting that maybe the majority of individuals in these study populations may be colonised!

In our labs, it was an exciting year as well. My colleagues and I published papers on a new real-time PCR for Blastocystis, a multilocus sequence typing system for Blastocystis sp. ST3 and ST4 showing that barcoding is a good proxy for intra-genetic diversity, and papers on surveys of specific cohorts in Sweden, Brazil and Australia. I published a paper on some of my thoughts on Blastocystis in Trends in Parasitology and a paper in Journal of Clinical Microbiology comparing two commonly applied PCR methods for subtyping Blastocystis - barcoding versus STS-PCR -, ending up recommending barcoding, although this method also has its limitations.

Overall, this has been an exciting year for people in Blastocystis research, and my colleauges and I are publishing a review on the recent advances in Blastocystis research in the beginning of 2013 in Advances in Parasitology. Next year will also see some publications stemming from the PhD study by our colleague Mohammed Alfellani (London School of Hygiene and Tropical Medicine), who made a great effort of sampling from humans and animals in different geographic locations and he has a lot of very interesting observations, which I'll get back to once the papers have been published. I'm sure that in 2013 there will be many more survey papers, but what I'm looking particularly forward to is the potential "omics" papers, - authors reporting on the nature and behaviour of Blastocystis, and papers aiming to make us understand Blastocystis in an ecological context. The genome for one Blastocystis subtype, namely ST7, is available, and more genomes will ensue in 2013 and 2014, enabling comparative genomic studies and studies of protein structure and function.

In our lab we recently attracted some significant funding and identified new possibilities for collaboration, so we are eager to get the wheels going!

This blog was put up just before April, and why not celebrating the turning of the year by having a second look at one or more of the most popular posts? You will find the list of "Popular Posts" in the right-most sidebar.

However, for those of you, who have a thing for Christmas: Merry Christmas! And a Happy New Year to all!

PS: This blog is now listed at Microbiology Blogs hosted by microBEnet and also at The Tree of Life blog by Prof Jonathan Eisen.


Poirier P, Wawrzyniak I, Vivarès CP, Delbac F, & El Alaoui H (2012). New insights into Blastocystis spp.: a potential link with irritable bowel syndrome. PLoS pathogens, 8 (3) PMID: 22438803

Tsaousis AD, Ollagnier de Choudens S, Gentekaki E, Long S, Gaston D, Stechmann A, Vinella D, Py B, Fontecave M, Barras F, Lukeš J, & Roger AJ (2012). Evolution of Fe/S cluster biogenesis in the anaerobic parasite Blastocystis. Proceedings of the National Academy of Sciences of the United States of America, 109 (26), 10426-31 PMID: 22699510

van Hellemond JJ, Molhoek N, Koelewijn R, Wismans PJ, & van Genderen PJ (2012). Is paromomycin the drug of choice for eradication of Blastocystis in adults? Journal of infection and chemotherapy : official journal of the Japan Society of Chemotherapy PMID: 23053509

Pandey PK, Siddharth J, Verma P, Bavdekar A, Patole MS, & Shouche YS (2012). Molecular typing of fecal eukaryotic microbiota of human infants and their respective mothers. Journal of biosciences, 37 (2), 221-6 PMID: 22581327

Hamad I, Sokhna C, Raoult D, & Bittar F (2012). Molecular detection of eukaryotes in a single human stool sample from Senegal. PloS one, 7 (7) PMID: 22808282

Scanlan PD (2012). Blastocystis: past pitfalls and future perspectives. Trends in parasitology, 28 (8), 327-34 PMID: 22738855

Machicado JD, Marcos LA, Tello R, Canales M, Terashima A, & Gotuzzo E (2012). Diagnosis of soil-transmitted helminthiasis in an Amazonic community of Peru using multiple diagnostic techniques. Transactions of the Royal Society of Tropical Medicine and Hygiene, 106 (6), 333-9 PMID: 22515992

Cañete R, Díaz MM, Avalos García R, Laúd Martinez PM, & Manuel Ponce F (2012). Intestinal parasites in children from a day care centre in matanzas city, cuba. PloS one, 7 (12) PMID: 23236493

Stensvold CR (2012). Comparison of sequencing (barcode region) and STS PCR for Blastocystis subtyping. Journal of clinical microbiology PMID: 23115257

Engsbro AL, & Stensvold CR (2012). Blastocystis: to treat or not to treat ... But how? Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 55 (10), 1431-2 PMID: 22893582

Stensvold CR (2012). Thinking Blastocystis out of the box. Trends in parasitology, 28 (8) PMID: 22704911

Stensvold CR, Ahmed UN, Andersen LO, & Nielsen HV (2012). Development and evaluation of a genus-specific, probe-based, internal-process-controlled real-time PCR assay for sensitive and specific detection of Blastocystis spp. Journal of clinical microbiology, 50 (6), 1847-51 PMID: 22422846
Forsell J, Granlund M, Stensvold CR, Clark CG, & Evengård B (2012). Subtype analysis of Blastocystis isolates in Swedish patients. European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology, 31 (7), 1689-96 PMID: 22350386

Malheiros AF, Stensvold CR, Clark CG, Braga GB, & Shaw JJ (2011). Short report: Molecular characterization of Blastocystis obtained from members of the indigenous Tapirapé ethnic group from the Brazilian Amazon region, Brazil. The American journal of tropical medicine and hygiene, 85 (6), 1050-3 PMID: 22144442

Stensvold CR, Alfellani M, & Clark CG (2012). Levels of genetic diversity vary dramatically between Blastocystis subtypes. Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases, 12 (2), 263-73 PMID: 22116021  

Nagel R, Cuttell L, Stensvold CR, Mills PC, Bielefeldt-Ohmann H, & Traub RJ (2012). Blastocystis subtypes in symptomatic and asymptomatic family members and pets and response to therapy. Internal medicine journal, 42 (11), 1187-95 PMID: 22032439

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