Bacterial contamination and growth in two defined formula diets of different pH

We inoculated partially hydrolysed protein feed of low pH and an intact protein feed of neutral pH with various pathogenic bacteria, and showed that the low pH feed restricted bacterial growth. To study this effect in a clinical setting, 20 malnourished in-patients were randomised prospectively to receive one or other of these feeds. Both formulae were given as a continuous feed via a nasogastric tube, 1,000 ml over 12 h twice daily, using routine hygienic measures. On two occasions significant contamination was demonstrated (Erwinia herbicola and Acinetobacter Iwoffi), both occurring in the intact protein diet. When the bacteria were isolated and transferred to the hydrolysed protein diet, their growth was inhibited. The contamination did not cause clinical complications. The study demonstrates inhibition of microbial growth in a partially hydrolysed protein formula of low pH. This effect may reduce the risk of contamination, and limit infectious complications.