Attenuated Salmonella Gallinarum strain shows increased survival in primary chicken macrophage infection

Fowl typhoid is an important systemic disease in poultry of all ages caused by Salmonella enterica subsp. enterica serovar Gallinarum biovar Gallinarum (Salmonella Gallinarum). Previous studies in brown laying hens showed that the Salmonella Gallinarum 287/91 strain with defective cobS and cbiA genes (SGΔcobScbiA) is a potential vaccine candidate. During Salmonella pathogenesis, the host's innate immune system plays an important role, especially the macrophages. The present work compared the uptake and survival after 2-, 4-, and 20-hours post-infection (hpi) of the double mutant strain SGΔcobScbiA with the wild-type strain during HD-11 chicken macrophage-like cell line and primary chicken macrophage infection. In the assays, primary macrophages more accurately mimicked in vivo infection conditions, with the 2-, 4-, and 20-hpi significant difference, than the HD-11 cell line, which presented no difference at any time. Furthermore, at 2-hpi, SGΔcobScbiA exhibited a higher fold increase from the uptake phase and a higher survival rate than the wild-type strain. In sum, primary chicken macrophages demonstrated an efficient alternative to in vivo model experiments.