In vitro inhibition of Helicobacter pylori by dairy starter cultures

Sixty-three dairy starter cultures (single or mixed) grown in skim milk were screened against 5 strains of Helicobacter pylori (ATCC 43504, ATCC 43579, UA 799, UA 801 and UA 802). Preliminary screening revealed 25 strains with anti-Helicobacter activity. These include strains of Lactobacillus casei, Lb. delbrueckii, Lb. helveticus, Lb. acidophilus and Lactococcus lactis. A standard well plate assay method was employed to examine the inhibitory zones from skim milk cultures. Washed cells harvested from MRS medium were also evaluated using a direct, spot-on lawn method. Both washed cells and skim milk cultures showed inhibitory action. As indicated by zone measurements, skim milk cultures showed stronger inhibition towards H. pylori than did the washed cells. Among the H. pylori strains tested, ATCC 43504 and ATCC 43579 were more susceptible while UA 799 was the least. Many of the positive cultures showed a strong synergistic action on the inhibition of H. pylori. Our results also confirmed that acids produced by the dairy lactics are partly responsible for the inhibitory action.