The AroC gene is required for pathogenicity and antibiotic sensitivity in Edwardsiella tarda strain ET13

Abstract

Edwardsiella tarda (E. tarda) is a significant enteric pathogen responsible for causing diarrhea, wound infections, and fatal septicemia in humans, as well as various aquatic animals. To investigate the role of the aroC gene in E. tarda’s pathogenicity and antibiotic sensitivity, the ΔaroC mutant and aroC⁺ complemented strains of ET13 were constructed. Our in vitro experimental data showed that the ET13ΔaroC mutant failed to grow in Defined Minimal Medium (DMM) broth without aromatic amino acids and exhibited significantly reduced growth compared to the wild-type ET13WT and complemented ET13aroC⁺ when aromatic amino acids were supplemented. This indicates that the aroC gene is essential for the growth of E. tarda in the DMM medium. Notably, the ET13ΔaroC mutant displayed significantly reduced adhesion, invasion, and intracellular replication in Caco-2 cells compared to the ET13WT and ET13aroC⁺. Furthermore, the ET13ΔaroC mutant exhibited a reduction in biofilm formation ability and increased sensitivity to antibiotics. The 50% lethal dose (LD₅₀) of ET13ΔaroC increased to 4.8 × 10⁴ CFU, representing a nearly 5-fold increase compared to ET13WT and ET13aroC⁺. In addition, ET13ΔaroC exhibited reduced colonization in the kidney and spleen of Zebrafish. Notably, the impaired virulence phenotypes of ET13ΔaroC were observed even in nutrient-replete conditions (e.g., LB medium), indicating that these defects are not solely attributed to aromatic amino acid auxotrophy and instead point to a role of aroC beyond supporting bacterial growth. Collectively, our data demonstrate that the aroC gene is required for key virulence-associated phenotypes (adhesion, invasion, intracellular replication, and biofilm formation) and modulates antibiotic sensitivity in E. tarda strain ET13.