FOS and infection: When FOS or GOS were combined with RBL67 (R-FOS and R-GOS) during periods 2–4, N-15 counts decreased even more rapidly compared to treatments with the prebiotics alone, reaching non-detectable levels after two days post-infection (periods 2 and 3) or reducing initial N-15 counts by approximately 2 log10 cfu/mL (period 4).