In a large US-based study of more than 400 infants, researchers found that about 1 in 4 babies were missing an important group of gut bacteria called Bifidobacterium.
These microbes play an important role in early immune system development. Their absence was associated with a higher risk of allergies, eczema, or asthma by age 2.
Researchers followed 412 infants from 48 states and collected fecal samples from them at 1 to 3 months of age. Using DNA analysis, they studied the types of bacteria that were present in each sample.
They found that 24% of the infants had no detectable Bifidobacterium, including 35% of those delivered via cesarean section and 19% of those born vaginally. The bacteria were especially scarce in breastfed C-section babies, while other microbes, including potentially harmful species, dominated the gut.
The team grouped infants into 3 microbiome clusters based on bacterial composition. One group, which accounted for 24% of the infants, had high levels of Bifidobacterium, particularly Bifidobacterium breve, and showed the lowest rates of allergic conditions by age 2. The other 2 groups—which comprised 76% of the infants in the study—had low or absent Bifidobacterium and were 3 times more likely to develop atopic conditions.
The presence of B. breve was especially protective. Infants with this species had nearly 5 times lower risk of developing allergic disease. Another species, Bifidobacterium longum, showed a potential benefit, though the reduction in risk was not statistically significant. More specifically, B. longum, B. breve, and Bifidobacterium infantis were positively associated with metabolites that are "critical" for immune and cognitive development, lead author John B. Jarman of Persephone Biosciences in San Diego wrote with colleagues.
The researchers also examined how the microbes functioned. In infants who lacked Bifidobacterium, other bacteria—such as Clostridium perfringens—consumed human milk sugars, a nutrient typically used by Bifidobacterium. These substitute microbes have been linked to inflammation and disease in other studies.
The gut chemistry also differed based on microbial makeup. Infants without Bifidobacterium had lower levels of health-supporting substances like thiamine and indole-3-lactate, and showed higher levels of antimicrobial resistance and virulence genes, which are associated with disease-causing bacteria.
By age 2, 30% of the infants had at least one diagnosed condition: eczema, allergies, or asthma. The risk was similar to that seen in infants who had taken antibiotics during their first 2 years.
These findings suggest that early gut bacteria composition can influence immune development and long-term health. Notably, even among vaginally delivered and breastfed babies, Bifidobacterium was not always present. The researchers plan to continue tracking the cohort to better understand how early microbiome patterns affect health later in childhood.
Full disclosures can be found in the published study.
Source: Communications Biology