Acidity and intestinal bacteria: an in-vitro assessment of the bactericidal activity of hydrochloric acid on intestinal pathogens.

The bactericidal activity of hydrochloric acid (HCl) on different intestinal bacteria was evaluated at various pH values and time intervals. The effect of HCl was highest at pH 2 and pH 3 on strains of Campylobacter jejuni, Aeromonas hydrophila, Plesiomonas shigelloides, Yersinia enterocolitica, Salmonella spp. and Shigella spp., producing complete killing after 60 min incubation. However, at higher pH values (pH 4 and above), these organisms not only survived but they also showed evidence of rapid multiplication. In contrast, clinical and standard strains of Escherichia coli and Staphylococcus aureus were resistant to all the pH values. Highest sensitivity to HCl was observed with strains of Shigella spp. and Salmonella spp. It is conceivable that patients with normal gastric acidity should not suffer from gastroenteritis caused by these intestinal pathogens.