Polyphenol-rich plant extracts inhibit Lawsonia intracellularis in two complementary bioassays

Porcine intestinal adenomatosis (PIA) is a disease of the gastrointestinal tract of grower piglets, caused by the Gram-negative bacterium Lawsonia intracellularis (LI). It is characterized by excessive proliferation of infected enterocytes, leading to ineffective digestion, reduced nutrient absorption and diarrhea. It is common practice to control the disease by temporary use of antibiotics during the critical phase. However, prudent use of antibiotics in animal production is imperative, which may be supported by alternative control strategies. Feed additives like organic acids, probiotics or phytogenics have shown the potential to substitute antibiotics in other contexts before. Here, we report on the antibacterial activity of plant-derived samples against LI in two especially developed in vitro bioassays. In vitro research on LI is complicated because the bacterium requires animal host cells to proliferate. In the first assay, antibacterial effects of samples were determined after fluorescent staining by a viability test kit and evaluation by flow cytometry. The second approach involved McCoy's mouse fibroblasts, which were infected by LI and the effect on bacterial proliferation was measured after fluorescent antibody staining and evaluation by a microplate fluorescence reader. Both assays allowed simple and automatised testing and several plant-derived samples showed anti-lawsonial activities in one or both approaches. Water extracts of oak and chestnut wood inhibited LI viability and proliferation as determined by both assays. These materials are known to be rich in polyphenols. The identity of active compounds however remains to be revealed. Furthermore, field trials under practical farming conditions shall clarify if phytogenics may offer comparable protection against PIA as currently used antibiotics.

Acknowledgements: Financial support by the Austrian Research Promotion Agency (FFG) is gratefully acknowledged.

Keywords: Lawsonia intracellularis, PIA, oak, chestnut, in vitro bioassays