The interesting letter of Dr. Stevens approaches several different aspects of the question of the denomination of the strain Saccharomyces boulardii.
To avoid any confusion, we consider it useful to differentiate these different aspects.
(i) From an identification and differentiation point of view, clearly, conventional biochemical characteristics cannot be used to unambiguously separate strains of Saccharomyces cerevisiae themselves and to distinguish S. cerevisiae from S. boulardii (1-3). But in a recent study, both multilocus enzyme electrophoresis and restriction polymorphism of mitochondrial DNA were able to clearly distinguish S. boulardii from S. cerevisiae (M. Mallié, P. Van Nguyen, S. Bertout, and J. M. Bastide. Abstr. 14th Congr. Int. Soc. Hum. Anim. Mycol. 2000, abstr. 511.)
(ii) From a classification point of view it can be discussed whether the particular strain S. boulardii has to be included in the species S. cerevisiae or outside it. Some authors, such as Cardinali and Martini (1-1) and McFarland (1-4), consider that S. boulardii is just outside the species S. cerevisiae. Others, such as Mallié et al. (Abstr. 14th Congr. Int. Soc. Hum. Anim. Mycol. 2000), consider that according to current scientific taxonomy, S. boulardii should be considered as part of S. cerevisiae; they consider it an original strain and propose the name S. cerevisiae var. boulardii. Clearly, this is still a debated subject and the paper by Dr. McCullough et al. (1-3) has probably not closed the discussion.
(iii) Finally, Dr. Stevens questions the fact that we study S. boulardii but no strain of S. cerevisiae. It is an interesting academic question, but we confirm that our studies have focused on lyophilized S. boulardii, which is a marketed product of which Laboratoires Biocodex want to extend the scientific knowledge, encouraging research to further elucidate its mode of action.
In fact, there has been at least one study testing different stains of Saccharomyces. Castagliuolo et al. tested both S. boulardii and another strain (S. cerevisiae ATCC 32167) and found that only S. boulardii exhibited antidiarrheal effects in the rat ileal loop model (1-2).
Does the fact that we have not studied others strains of Saccharomyces invalidate the value of our research and the interest in reporting it?
REFERENCES
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