I should also mention that "Prescript-Assist" is the only probiotic that I know of that contains genus Bacteroides bacteria. Bacteroides are considered to be the most prevalent of all bacteria in the gut, especially the colon.
"Anaerobes make up the majority of bacteria found in the bacterial flora found in the human colon; the most predominant bacteria found are Bacteroides. The colon contains over 400 species of organisms and has more than 10^11 organisms per gram of wet weight. Bacteroides by themselves constitute nearly 10^11 organisms per gram of feces (dry weight). "