Effects of humic acids on the recovery of different bacterial strains in an in vitro chicken digestive model.

Humic acids (HA) have been evaluated as growth promoters in poultry, but their effects on the gut microbiota remains controversial using in vitro and in vivo models. The objective of this study was to determine the effect of HA extracted from a wormcompost on the recovery of bacteria: Salmonella Enteritidis (S. Enteritidis), Escherichia coli (E. coli), Clostridium perfringens (C. perfringens), Bacillus subtilis (B. subtilis) and Lactobacillus salivarius (L. salivarius) using an in vitro chicken digestive system. Independent in vitro trials were run for each bacteria using six treatments: 1) Negative control with no bacteria added (Control-), 2) Positive control added with bacteria (Control+), 3) 0.1% HA + bacteria, 4) 0.2% HA + bacteria, 5) 0.5% HA + bacteria and 6) 1% HA + bacteria. Data was subjected to analysis of variance and linear regression. In the crop, S. Enteritidis was lower, C. perfringes and B. subtilis were not affected by HA, while E. coli and L. salivarius were higher at 0.5 and 1% HA inclusion (P ≤ 0.0001). In the proventriculus, S. Enteritidis, E. coli and B. subtilis were higher at 0.5 and 1% HA inclusion (P ≤ 0.0001); C. perfringens and L. salivarius were not affected by HA. In intestine, significant increases of all bacteria strains were observed (P ≤ 0.0001). In conclusion, the results suggests that HA can be used as prebiotic, but their mechanisms of action to stimulate the growth of gut bacteria remains to be elucidated.