THE EFFECT OF PH ON THE INHIBITION OF BACTERIAL-GROWTH BY PHYSIOLOGICAL CONCENTRATIONS OF BUTYRIC-ACID - IMPLICATIONS FOR NEONATES FED ON SUCKLED MILK

Butyric acid is released from milk by pre-intestinal lipases during su ckling. It is also known to inhibit bacterial growth. To investigate w hether butyric acid may be a significant factor in controlling bacteri al growth in the stomach of pre-weaned animals, the ability of butyric acid to inhibit growth of selected bacteria was tested over physiolog ical ranges of pH and butyric acid concentrations. Six enteric and env ironmental strains of bacteria were used: two strains of Escherichia c oli, Klebsiella pneumoniae, Enterococcus faecium, Enterococcus faecali s, and Enterococcus casseliflavus. At pH 4.5 and 5.0, the growth of al l organisms was significantly inhibited in the presence of butyrate, a nd in some cases growth was completely arrested. At pH 6.0, butyric ac id did not affect bacterial growth until the concentration reached 40 mM. The maximum concentration of butyric acid available in cow's milk after incubation with pre-gastric lipase is approximate to 16 mM, whic h would be sufficient to prevent growth of the organisms tested at pH values occurring in the stomach. Therefore, butyric acid inhibition of bacterial growth may explain in part, the role of pre-intestinal lipa ses in young animals' natural defenses against bacteria in ingested fo od prior to weaning. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.