I would like to highlight a comment that we published in PLoS Pathogens, - a paper that is free for download
here. It gained some attention on Twitter, and it was recently
reviewed in the Faculty of 1000.
We basically highlight the tricky situation that we so often encounter in the field of clinical microbiology, namely the one in which all non-fungal organisms isolated from the human intestinal tract are being referred to collectively as 'parasites'. The word 'parasite' has a negative connotation, indicating that the organism exploits the host with
detrimental effects on the host. While this is true for some ciliates, for instance
Giardia, other ciliates may in fact be mutualists, which means that these organisms have adapted to a life within a host, providing the host with one or more advantages. One such example is seen in herbivores, where ciliates and flagallates break down cellulose.
In the clinical microbiology lab we face different types of organisms when dealing with stool samples:
Giardia,
Cryptosporidium and
Entamoeba histolytica are considered true parasites, i.e. organisms benefitting from the environment of a host, at the expense of the host, and symptoms such as diarrhoea may develop, indicating host damage. Parasites such as
Cryptospordium are usually infecting an individual for a short while, with immunity developing. Meanwhile, we also encounter eukaryotic organisms that are known to be able to colonise the intestine for a very long time, - decades, without being expelled by the host;
Blastocystis belong to this group. For some reason it is as if the body 'tolerates' the presence of the organism. Maybe
Blastocystis is good at evading local immune responses, or maybe the body wishes to 'keep'
Blastocystis for some reason and so developed a way to tolerate it... as I've hinted at before on this blog, maybe
Blastocystis may assist us in one or more metabolic processes, for instance, either directly or indirectly, maybe by selecting for or influencing bacterial communities. Indeed, we recently found evidence of
Blastocystis being specifically related to certain groups of bacteria, which, if confirmed, opens up for a whole new line of research, including the use of
Blastocystis as a probiotic.
I know that this last sentence may sound harsh in some people's ears; nevertheless, most research involving
Blastocystis so far has been quite static and unimaginative, and it's about time that food microbiologist and the like start taking an interest in the micro-eukaryotes that tend to be common and stable conolisers of our guts.
If YOU take an interest in this topic, I suggest you look up the articles cited below.
References and further reading:
Andersen LO, Bonde I, Nielsen HB, & Stensvold CR (2015). A retrospective metagenomics approach to studying Blastocystis. FEMS Microbiology Ecology, 91 (7) PMID: 26130823
Lukeš J, Stensvold CR, Jirků-Pomajbíková K, & Wegener Parfrey L (2015). Are Human Intestinal Eukaryotes Beneficial or Commensals? PLoS Pathogens, 11 (8) PMID: 26270819
