Infant colonization by Staphylococcus aureus: role of maternal carriage.

Infant colonization by Staphylococcus aureus has not been adequately investigated. In this study, we aimed to define determinants associated with the carriage of S. aureus in early infancy. Serial nasal swabs were collected from 128 infants and their mothers at months 0, 6, and 12 postpartum. S. aureus isolates were characterized by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), spa typing, and the presence of chromosomal mecA and of Panton-Valentine leukocidin (PVL) genes. S. aureus was isolated in 17.7% and 15.7% of swabs from infants and mothers, respectively. Carriage rates were higher in infants with carrier mothers, non-smoking mothers, and many siblings. Persistent carriage rates were higher in infants with carrier or non-smoking mothers. S. aureus typing revealed identical strains in 10/15 investigated infant-mother pairs. Among 19 investigated S. aureus isolates from infants, ten harbored mecA and two harbored PVL genes, and these determinants were concomitantly present in isolates from mothers. Resistance to methicillin was 43.6% among all isolates from infants. In conclusion, isolates from infants were commonly identical to isolates from their mothers, pointing to a principal role of maternal carriage in S. aureus colonization in infants.