From my research, I have found that currently marketed probiotics don't permanently colonize the gut. Some of these strains were originally isolated from dairy foods or fermented foods, and are strangers in the human gut. And the human-derived species of Lactobacilli and Bifidobacteria mentioned are often only transiently present in the human gut.
These manufacturers looked for microbes that would be culturable, tolerant to the acidic environment of fermented milks and yogurts (which Lactobacilli can tolerate, unlike other human intestinal species); that would be resilient in environments that have oxygen (unlike most gut anaerobes, many Lactobacilli have some tolerance to oxygen and can survive food packaging processes); and that would be resilient to the shear forces encountered during food manufacture (Lactobacilli and Bifidobacteria have thick cell walls that can sustain high-shear food production processes such as blending.
Our guts have hundreds if not thousands of types of bacteria. If multiple uses of antibiotics have killed off most of your commensal bacteria, or a large portion to allow Candida to overgrow--how are probiotics from the store going to help since they only contain 5-10 strains? What about the hundreds/thousands missing?
Dr. Jeff, why are most of your testimonials primarily about people losing weight and are happy based on cosmetic reasoning? Have you ever cured systemic problems? Where are the systemic Candida testimonials?