Does gastric acid protect the preterm infant from bacteria in unheated human milk?

Although preterm mother's milk has greater nutritional and anti-infective properties than donor milk, it may be highly contaminated with bacteria. We therefore asked three questions: what is the fate of these bacteria in the preterm infant's stomach, is gastric pH important, and what factors affect gastric pH? pH, colony count and bacterial identification were performed on the milk and on serial gastric aspirates in 20 preterm infants on 25 occasions. Seventeen milk samples grew bacteria, five potentially pathogenic and 12 non-pathogenic. Twelve of 25 prefeeding gastric samples were sterile, but following the feeding all the samples grew non-pathogenic bacteria and 70% grew potential pathogens. With time pH decreased and by 2-h samples with pH < 3.5 had no bacterial growth; Candida albicans still flourished in a low pH (mean 2.8). We concluded that a low gastric pH may be more important than the bacterial count of the milk. In a second study, 91 serial gastric pH measurements were made on 12 preterm infants, pH tended to decrease with increasing age and was significantly lower in infants fed exclusively human milk (2.7 vs. 3.6; human milk versus formula P < 0.02) We speculate that human milk may influence gastric acid production and thus protect the preterm infant from bacteria in the milk.