Effects of <i>Bifidobacterium animalis</i> Subsp. <i>Lactis</i> <scp>CP</scp> ‐9 on Gut Microbiota and Immune Functions in Healthy Infants

Infancy represents a critical period for growth and development, during which the gut microbiota and its metabolites play essential roles in nutrient absorption and maintaining health. Therefore, it is of great significance to evaluate the safety and gut microbiota-modulating effects of specific probiotics in healthy infants. This study aimed to investigate the effect of Bifidobacterium animalis subsp. lactis CP-9 strain (CP-9) on healthy infants aged 6 to 36 months and its relationship with growth patterns and multidimensional indicators. In this randomized, double-blind, placebo-controlled trial, healthy infants were randomly assigned to receive CP-9 or placebo for 3 months. Safety, growth parameters, complete blood counts (CBC), immunological markers and faecal microbiota were assessed before and after the intervention. All infants exhibited age-appropriate growth in height and head circumference during the study. The CP-9 strain significantly increased gut Bifidobacterium abundance and regulated the microbiota-mediated polyunsaturated fatty acids biosynthesis pathway. Haematological and systemic inflammatory markers remained within normal ranges and no treatment-related adverse changes were detected during the 3-month intervention period. Moreover, CP-9 improved stool characteristics and gastrointestinal tolerability, with no increase in the incidence of respiratory allergies, skin allergies, respiratory infections, or fever, which further confirmed its safety. These findings suggested that CP-9 supplementation resulted in significant enrichment of Bifidobacterium, a beneficial gut bacterium and had no detectable adverse effects on the measured physiological parameters. Consequently, the intervention raised no detectable safety concerns in healthy infants under the conditions of this study. Given this, CP-9 is a probiotic that does not show any obvious short-term safety signals for infants aged 6 to 36 months.