Inner membrane protein TolA facilitates the antibiotic resistance, environment adaptability, biofilm formation and virulence of avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) can cause colibacillosis, which is economically devastating to poultry industries worldwide. The bacterial membrane is critical to its environment adaptability and virulence. The inner membrane protein TolA maintains membrane integrity, but its roles in the fitness and pathogenesis of APEC are not completely understood. Thus, a tolA gene mutant and complemented strains of APEC were constructed and characterized. Mutant strain ΔtolA showed damage in the inner and outer membranes, as well as altered morphology, impaired flagella production, reduced motility, increased outer membrane vesicle (OMV) production, and reduced resistance to antibiotics and environmental stress. Deletion of the tolA gene resulted in significant reductions in biofilm formation and interbacterial competition, due to the downregulated expression of biofilm-associated genes and type Ⅵ secretion system (T6SS) genes, respectively. In addition, the mutant strain exhibited reductions in serum bactericidal resistance, cell infection capacity, intracellular survival, consequently leading to attenuated bacterial survival and virulence in mice. Compared with the wild-type and complemented strains, the mutant strain induced less expression of inflammatory cytokine interleukin 1 beta (IL-1β) in HD-11 macrophages, consistent with the pathological damage in mice. In conclusion, inner membrane protein TolA contributes to the antibiotic resistance, environmental adaptability, biofilm formation and virulence of APEC.