Showing posts with label Fasting. Show all posts
Showing posts with label Fasting. Show all posts

Saturday, July 7, 2012

Blastocystis Nutrition

A reader of this blog asked me about the nutritional requirements of Blastocystis and whether I thought the parasite can be eradicated by fasting.

Given my background (I'm not a dietitian for starters), I guess my best way of approaching this is by drawing on my experience from the lab. When we diagnose Blastocystis, we have multiple methods to choose from, some of which are better than others (please look up previous posts here for more information). Short term (i.e. 24-48 h) in-vitro culture at 37 °C in Jones' medium is almost as sensitive as PCR (molecular detection). This means that if viable Blastocystis is present in a faecal sample, then it will most probably "come up" in culture, which means that in a day or two, we will be able to detect those "characteristically non-characteristic" soap bubble structures (the vacuolar stage) by light microscopy of a small portion of the culture - they will be all over the place!

So, what's Jones' medium? Well, Blastocystis can be cultured in a variety of different media, some of which are very primitive. Jones' medium is probably one of the simplest media, and consists mainly of electrolytes, yeast extract (contains nucleic acids) and horse serum (containing lipids). Importantly, we don't even have to add starch to the medium, when we culture Blastocystis xenically (i.e. under non-sterile conditions and this is what we always do when using culture diagnostically). Blastocystis has also been grown in a saline-serum medium, again in the presence of bacteria.

Apart from providing the anaerobic environment required for Blastocystis to thrive, bacteria most probably constitute a significant source of nutrients for the parasite. We can consistently keep strains of Blastocystis in xenic culture for weeks, months, years, observing vigorous growth, and it is clear that the bacteria and the simple medium supply nutrients in abundance. I have never managed to axenise (i.e. eliminate bacteria from) a culture, but others have been successful at times. One of the pioneers in Blastocystis research, Charles H. Zierdt, noted that the axenisation of Blastocystis usually takes weeks/months with a continuous reduction of bacterial numbers and species, until one species, usually a Bacteroides sp., remains; elmination of the last bacterial species may or may not result in axenisation, simply depending on the need for bacterial support. One of our future goals is to characterise the bacterial flora in individuals with and without Blastocystis.

I believe that even during fasting, Blastocystis will have plenty of access to essential nutritional components. It is possible that fasting may impact the intestinal bacterial flora, and if Blastocystis is dependent on a certain bacterial flora, it may be so that the parasite can be "manipulated" by manipulating the intestinal flora.

Useful reading:

Clark CG, & Diamond LS (2002). Methods for cultivation of luminal parasitic protists of clinical importance. Clinical microbiology reviews, 15 (3), 329-41 PMID: 12097242
Zierdt CH (1991). Blastocystis hominis--past and future. Clinical microbiology reviews, 4 (1), 61-79 PMID: 2004348