Fig. 5. Acid tolerance of H. pylori. Acid tolerance of H. pylori at 20, 40, and 60 min in the pH 4 buffer was assayed by mixing H. pylori CPY3401 with K. denitrificans NHP1, K. denitrificans ATCC3394, and buffer alone. Percent survival of H. pylori CPY3401 at pH4 condition in contrast to pH 7 condition was calculated by comparing the numbers of colonies.