Introduction: The neonatal gut undergoes massive microbial colonisation starting at birth, influenced by maternal microbiota, human milk, and the surrounding environment. Human milk, with its unique composition and antimicrobial properties, fosters a bifidobacteria-dominant microbiota, whereas formula-fed infants have a more diverse microbiome with often reduced bifidobacterial and increased clostridial representation. Despite their lower abundance and detection challenges, clostridia are among the important commensal members of the infant gut microbiota. This study investigates whether human milk affects the occurrence of clostridia at the species and strain level.
Methods: The growth ability of 30 infant strains of various clostridial species in pasteurised human milk, infant formula, control glucose–peptone, and a nutrient-poor medium was tested in microtiter plates at 37 °C under anaerobic conditions. After 24h incubation, the cultivation counts were determined and related to the real inoculation dose.
Results: Human milk supported the growth of C. perfringens, while C. tertium, C. butyricum, Clostridioides difficile, and Paeniclostridium sordellii were inhibited, and Paraclostridium bifermentans only survived. Infant formulas allowed the growth of C. perfringens, P. bifermentans, and C. tertium. All strains tested used control medium, and some even used a nutrient-poor medium.
Conclusions: C. perfringens was the most competent in utilising human milk and infant formulas of all the clostridial species tested; however, this ability was highly strain-specific and likely reflected the origin of the strain and milk. Human milk appears to significantly regulate the growth of several clostridial species, except for C. perfringens, which probably possesses adaptive mechanisms that allow human milk utilisation despite milk's antimicrobial nature. These findings suggest a regulatory role of early nutrition in modulating the occurrence of clostridia in the infant gut.
Acknowledgements: This work was supported by a grant LUAUS23014 (MEYS, CZ) and METROFOOD-CZ research infrastructure project (MEYS Grant No: LM2023064) including access to its facilities.