title: Edwardsiella tarda evades serum killing by preventing complement activation via the alternative pathway.
abstract: Edwardsiella tarda is a Gram-negative bacterium with a broad host range that includes a wide variety of farmed fish as well as humans. E. tarda has long been known to be able to survive in host serum, but the relevant mechanism is unclear. In this study, we investigated the fundamental question, i.e. whether E. tarda activated serum complement or not. We found that (i) when incubated with flounder serum, E. tarda exhibited a high survival rate (87.6%), which was slightly but significantly reduced in the presence of Mg(2+); (ii) E. tarda-incubated serum possessed strong hemolytic activity and bactericidal activity, (iii) compared to the serum incubated with a complement-sensitive laboratory Escherichia coli strain, E. tarda-incubated serum exhibited much less chemotactic activity, (iv) in contrast to the serum incubated with live E. tarda, the serum incubated with heat-inactivated E. tarda exhibited no apparent hemolytic capacity. Taken together, these results indicate for the first time that E. tarda circumvents serum attack by preventing, to a large extent, complement activation via the alternative pathway, and that heat-labile surface structures likely play an essential role in the complement evasion of E. tarda.
authors.affiliation: Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China; Graduate University of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Mo-fei
authors.initials: MF
authors.lastname: Li
authors.affiliation: Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China. Electronic address: lsun@qdio.ac.cn.
authors.forename: Li
authors.initials: L
authors.lastname: Sun
authors.affiliation: School of Biological Sciences, Lake Superior State University, 650 W. Easterday Ave., Sault Ste Marie, MI 49783, USA. Electronic address: jli@lssu.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: Li
mesh_terms: D000818:Animals; D003167:Complement Activation; D015941:Complement Hemolytic Activity Assay / Q000662:veterinary; D020609:Edwardsiella tarda / Q000276:immunology*; D004756:Enterobacteriaceae Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D005393:Fish Diseases / Q000276:immunology* / Q000382:microbiology; D005412:Flatfishes
keywords: Bacteria; Immune evasion; Serum resistance; Virulence