Background Most probiotic products rely on in vitro laboratory tests to assess transit and lack data on survival through the human gastrointestinal tract (GIT). However, in vitro tests are not representative of the multiple physiological states of the gut.

Aim To confirm transit of the Bifidobacterium longum 35 624 strain, found in Alflorex^®, in different formats in humans.

Method 35 624 strain was administered in a capsule, straw, sachet or milk format to volunteers for 7 days at doses ranging from 1x10⁷–1 × 10¹⁰ CFU/day (n=1–6) followed by a wash-out period. The transit of viable 35 624 strain through the human GIT was assessed from stool collected at various timepoints by bifidobacteria selective agar plates and/or typing representative colonies using strain-specific PCR.

Results Independent of form, the 35 624 strain transited in humans to high numbers, ranging from 1 × 10⁴ – 1 × 10⁸ CFU/g of stool in a dose-dependent manner at Day 7. Furthermore, despite antibiotic use in a 10-year-old cystic fibrosis sufferer (250 mg Zithromax 3 times/week), the 35 624 strain transited well (≥1 × 10⁶ CFU/g). Co-administration of the antibiotic and probiotic resulted in a 1 log decrease in levels recovered from stool compared to administration of the probiotic 12 hour post antibiotic.

Conclusion Independent of delivery format, the 35 624^® strain was detected in stool at day 7 in a viable form at levels greater than 1×10⁴ CFU/g of stool. Transit of viable 35 624^® strain in a patient with long term antibiotic use was confirmed demonstrating that the Zithromax did not affect the 35 624^® viability under the conditions of the experiment.