Survival of pathogenic microorganism in an acidic environment in the presence of a cow milk based infant formula

Human milk is known to have a lower acid buffering capacity than cow milk based infant formula (IF). The low buffer behavior of human milk is thought to complement the weak acid production of the infant stomach allowing retention of the lower pH environment. An IF with a lower buffering capacity (LBIF) designed to match the buffering pattern of the human milk could resemble the functionality by allowing a lower gastric pH environment which might inactivate orally ingested pathogens. Reconstituted IF was inoculated with Enteropathogenic E. coli (EPEC), Cronobacter sakazakii (C. sakazakii), and Salmonella enterica (10 4 to 10 5 CFU/ml). The pH of a control IF was adjusted to pH 4 or 3 and the same amount of acid was added to LBIF. Following 120 min the bacterial numbers were significantly lower for Salmonella and C. sakazakii in the LBIF compared to the control IF at pH 4. In contrast the population of C. sakazakii was higher in the LBIF at pH 3 but for both IF's the numbers of C. sakazakii decreased significantly over time. At pH 3 the EPEC population was significantly lower in the LBIF compared to the control IF. For Salmonella the difference between the two formulas was not consistent over time, but there was a 2 log 10 CFU/ml reduction for both. Depending on the bacterial strain the survival of pathogens was affected in the presence of a complex milk matrix in an acidic environment. Research support by Mead Johnson Nutrition