human biology - Do probiotics survive digestion?

Apparently, some do and some don't.

I just tried searching for yogurt lactobacillus survival on Google, and the first hit I got was an article titled "Survival of yogurt-containing organisms and Lactobacillus gasseri (ADH) and their effect on bacterial enzyme activity in the gastrointestinal tract of healthy and hypochlorhydric elderly subjects" by Pedrosa et al. (1995), published in the American Journal of Clinical Nutrition, vol. 61, pp. 353–359. The abstract reads:

"The effect of the live bacterial yogurt cultures, namely Streptococcus thermophilus and Lactobacillus bulgaricus, and a mucosal adhering strain of Lactobacillus gasseri (ADH) on small intestinal and fecal bacterial characteristics was examined in 10 elderly subjects with atrophic gastritis and 23 elderly normal volunteers (11 received yogurt and 12 received ADH). Neither S thermophilus nor L bulgaricus was recovered from the stomach or small intestine of subjects fed yogurt or pasteurized yogurt. ADH was recovered from gastric or small intestinal aspirates in three of four subjects and in the stools of four of five subjects diagnosed with atrophic gastritis. In 11 of 12 normal subjects, ADH was isolated from stools. There was a significant reduction in fecal bacterial enzyme activity in both normal volunteers and subjects with atrophic gastritis after being fed with viable ADH. Adherent strains of bacteria such as ADH are likely to survive passage through the gastrointestinal tract and thus have greater metabolic effects."

---

Here's another result from the same search, "Survival and therapeutic potential of probiotic organisms with
reference to Lactobacillus acidophilus and Bifidobacterium spp." (PDF) by Kailasapathy & Chin, Immunology and Cell Biology (2000) 78, 80–88, which says:

"Lactobacillus delbrueckii ssp. bulgaricus and S. thermophilus (yoghurt starter cultures) are not bile resistant and do not survive the passage through the intestinal tract [Gilliland, 1978]. However, L. acidophilus and B. bifidum incorporated into the yoghurt starter culture have the ability to establish themselves among the gut flora [Tamime & Robinson, 1985]."

but also points out that, for survival in the gastrointestinal tract to matter, the bacteria must first survive long enough to get there:

"Strains of bifidobacteria used in some commercial products neither survive gastric transit nor product acidity during storage [Varnam & Sutherland, 1994]. [...] Eight commercial yoghurt samples claiming to contain viable bifidobacteria, sold in London, were enumerated for the presence of this organism. Only five of the eight yoghurts tested contained viable bifidobacteria at > 10⁶ per mL, while the remaining three did not contain any bifidobacteria [Masuda et al., 1993]. Modler and Villa-Garcia [1993] reported that bifidobacteria do not survive in several yoghurt products in North America, due to highly acidic conditions. [...] It is considered misleading to describe probiotic yoghurt as having health promoting properties unless the minimum level of viable cells is present at the expiry date."