Swanson Probiotics Dr. Stephen Langer's Ultimate 16 Strain ... Product Description. Our most popular probiotic with 16 unique strains for total-body wellness. Supports digestive health with beneficial bacteria. Acid-resistant and no refrigeration necessary. Due to supply issues, L. bulgaricus and B. infantis have been replaced by L. paracasei and L. gasseri. Dr. Stephen Langer's Ultimate 16 Strain ...