Department of Fish Diseases and Management, Faculty of Veterinary Medicine, Benha University, Moshtohor, Toukh 13736, Egypt.
Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762-6100, USA.
Vet Microbiol. 2013 Mar 23;162(2-4):858-865. doi: 10.1016/j.vetmic.2012.11.006. Epub 2012 Nov 9.
Edwardsiella ictaluri is a Gram-negative facultative intracellular pathogen causing enteric septicemia in channel catfish. Iron is an essential micronutrient needed for bacterial virulence, and to acquire iron, many Gram-negative bacteria secrete ferric iron chelating siderophores. The ferric hydroxamate uptake (Fhu) system consists of four genes (fhuC, fhuD, fhuB, and fhuA), and is involved in the uptake of hydroxamate type siderophores across bacterial membranes. However, the Fhu system and its importance in E. ictaluri virulence have been uninvestigated. Here, we present construction and evaluation of an E. ictaluri ΔfhuC mutant. The E. ictaluri fhuC gene was deleted in-frame by allelic exchange, and the mutant's growth in media and virulence in catfish were determined. Our results indicated that deletion of the E. ictaluri fhuC gene did not affect the growth of E. ictaluri largely in both iron-replete and iron-depleted media. Addition of ferric iron sources into the iron-depleted medium improved the growth of both E. ictaluri ΔfhuC and wild type (WT). Catfish mortalities indicated that E. ictaluri ΔfhuC mutant was attenuated 2.05-fold compared with the parent strain. The catfish immunized with the E. ictaluri ΔfhuC mutant showed a high relative percent survival rate (97.50%) after re-challenge with the WT E. ictaluri strain. Taken together, our data indicates that the fhuC gene contributes to E. ictaluri virulence.
爱德华氏菌是一种革兰氏阴性兼性细胞内病原体，可引起斑点叉尾鮰肠道败血症。铁是细菌毒力所必需的微量元素，为了获取铁，许多革兰氏阴性菌会分泌三价铁螯合铁载体。铁羟肟酸盐摄取（Fhu）系统由四个基因（fhuC、fhuD、fhuB 和 fhuA）组成，参与细菌膜内外羟肟酸盐型铁载体的摄取。然而，Fhu 系统及其在爱德华氏菌毒力中的重要性尚未得到研究。在这里，我们构建并评估了爱德华氏菌ΔfhuC 突变株。通过基因交换，爱德华氏菌 fhuC 基因被缺失，然后检测突变株在培养基中的生长情况和在鱼类中的毒力。结果表明，爱德华氏菌 fhuC 基因的缺失在铁充足和铁缺乏的培养基中对爱德华氏菌的生长影响不大。向铁缺乏的培养基中添加铁源可以改善 E. ictaluriΔfhuC 和野生型（WT）的生长。鱼类死亡率表明，与亲本菌株相比，E. ictaluriΔfhuC 突变株的毒力降低了 2.05 倍。用 E. ictaluriΔfhuC 突变株免疫的鱼类在再次受到 WT E. ictaluri 菌株的攻击后，相对存活率达到 97.50%。综上所述，我们的数据表明 fhuC 基因有助于爱德华氏菌的毒力。
