Candida species as commensal gut colonizers: A study of 133 longitudinally followed Swedish infants.

The gut microbiota harbor a wide range of bacterial species, but also yeasts may be part of this ecosystem. Infants who are being treated in intensive care units are often colonized by Candida species. However, little is known regarding commensal yeast colonization of healthy infants and young children. Here the acquisition of yeast species was studied in a birth-cohort including 133 healthy Swedish infants. A rectal swab sample was obtained on day 3 of life, and fresh fecal samples were obtained at regular intervals up to 3 years of age; the samples were cultured quantitatively for yeasts. Colonization with yeasts increased rapidly in the first months of life, with 73/133 infants (55%) colonized at 6 months of age. The yeast numbers in positive samples decreased from an average of 105 cfu/g in infants aged 0-2 months to 103.5 cfu/g at 3 years of age. Candida albicans was the most frequently isolated species and reached higher population counts than the other species in culture-positive infants. The yeast colonization rate did not differ between infants who were delivered vaginally and those birthed via Caesarean section, whereas breastfed infants showed a lower colonization rate (p < 0.05 for 1 year of age compared to the other infants). The results demonstrate that yeasts, particularly C. albicans and C. parapsilosis (sensu lato), are common commensals in the gut microbiota of healthy infants and young children.