Intestinal flora in the second week of life in hospitalized preterm infants fed stored frozen breast milk or a proprietary formula.

Twenty infants fed stored frozen breast milk or a proprietary formula only had both aerobic and anaerobic cultures performed at a chronologic age of 8 to 14 days. Nine out of 10 stools from the infants fed stored frozen breast milk contained Enterobacteriaceae and one stool was sterile. One contained a Pseudomonas species; one contained anaerobic gram-positive rods; one contained anaerobic gram-negative rods; and four contained anaerobic gram-positive cocci. No anaerobes were found in six stools. Six stools had aerobic gram-positive cocci, none of which was hemolytic. Nine out of 10 stools from infants fed a proprietary formula had Enterobacteriaceae. Six stools had anaerobic gram-positive rods, three had anaerobic gram-negative rods, and four had gram-positive cocci. Four stools had no anaerobic bacteria. All 10 stools had nonhemolytic aerobic gram-positive cocci. Enterobacteriaceae were predominant in the stools of the infants fed either stored frozen breast milk or a proprietary formula, and the colony counts of aerobic bacteria were similar in both groups. This pattern of intestinal flora in hospitalized preterm infants in the second week of life is very different from that of normal term infants and may contribute to their increased incidence of systemic and localized infections. The use of stored frozen breast milk for the purpose of suppressing coliform and other potentially pathogenic organisms may not be effective in hospitalized preterm infants who have been treated previously with broad-spectrum, parenteral antibiotics.