Background Bacterial colonization during and shortly after birth are common in newborn infants. The aim of this study was to determine the umbilical cord bacterial colonization in newborn infants rooming in with mothers and neonates admitted to neonatal intensive care unit (NICU). Materials and Methods In a cross-sectional study, 180 newborn infants were studied in three groups including: newborn infants born via normal delivery and stayed with their mothers (n=60), newborn infants born by cesarean section and stayed with their mothers (n=60), and newborn infants admitted in NICU (n=60). Umbilical cord
care was done as natural drying without use of any disinfectant or local antibiotic for all newborn infants. Bacterial culture was performed on the second day in three groups and in days of 5-7 only among the infants admitted in NICU. Results Among the subjects, 50% (n=90) were boy and 50% (n=90) were the first-time mothers. Normal gestational age (38 to 42 weeks) was seen in 67.2% (n=121) of subjects. Three groups had no significant differences in terms of gender (p=0.247), and first-time mothers (p=0.344), but had a significant difference in terms of gestational age (p=0.001). Staphylococcus aureus was the most common bacteria responsible for the colonization in the first culture (n=31, 17.22%), and second culture (n=17, 13.5%). Bacterial colonization was more common in newborn infants who were born by cesarean section and stayed with their mothers compared to the other groups (p<0.001). Conclusion According to the study, bacterial colonization was common in newborn infants who were born by cesarean section and stayed with their mothers and Staphylococcus aureus had an important role in this colonization. Future study is recommended to confirm our results.