Gastric acid barrier to ingested microorganisms in man: studies in vivo and in vitro.

Reassessment of the ;gastric bactericidal barrier' to enteric bacteria in man included studies of the bactericidal activity of (1) the normal and achlorhydric stomach in vivo and (2) normal and achlorhydric gastric juice and other media in vitro. Within 30 minutes virtually all bacteria (Serratia marcescens) were eliminated in the normal stomach whereas no reduction occurred in the achlorhydric stomach in one hour. In vitro, identical bactericidal activity was observed at the same pH (from 2.0 to 7.0) in normal gastric juice, achlorhydric gastric juice, aqueous HCl, and nutrient broth. At pH less than 4.0, 99.9% of the bacteria were killed within 30 minutes. The presence of profuse bacterial flora, including coliforms, found in markedly acid-deficient but not in normal stomachs, correlates well with the absence of bactericidal activity. Thus, the ;gastric bactericidal barrier' is primarily pH-hydrochloric acid dependent, with other constituents of gastric juice contributing little, if any, detectable effect on the destruction of microorganisms.